| 0/0 |
2026/06/01 14:11 |
flow |
assessment-security |
57m
Results: map[DenialOfService:true Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the issue:
**Root Cause Analysis:**
The bug report shows several tasks hung in `D` state for over 143 seconds.
1. The `jbd2/sda1-8` thread (the journal commit thread for the `sda1` ext4
filesystem) is blocked in `wait_on_buffer()` within
`jbd2_journal_commit_transaction()`. It has submitted a metadata buffer to the
block layer via `submit_bh()` and is waiting for the block IO to complete (which
clears the `BH_Lock` bit).
2. Other tasks (`syz.*` and `kworker`) are blocked in `do_get_write_access()`
waiting for the `BH_Shadow` bit to be cleared on a buffer. This bit is cleared
by `journal_end_buffer_io_sync()` when the block IO for the committing
transaction completes.
This indicates a complete block IO stall on the `sda1` block device. The block
layer is not completing the submitted bios.
The presence of `nbd1-recv` workers in the lockdep output strongly suggests that
syzkaller has set up a user-space block device (like NBD, or a USB mass storage
device via `/dev/raw-gadget` backed by NBD/loop). If the user-space process
responsible for handling the IO for this block device (e.g., the syzkaller NBD
server or USB gadget emulator) stops responding, hangs, or intentionally sleeps,
the block IO will hang indefinitely. The kernel's block layer and the SCSI error
handler (which can also hang or loop if the device ignores resets) will wait for
the device, causing the filesystem mounted on it to hang.
This is a known and expected behavior when dealing with user-space emulated
block devices or failing hardware. The kernel cannot magically complete IO if
the underlying device or user-space emulator refuses to respond.
**Security Impact Assessment:**
* **Exploitable:** False. This is a pure IO hang leading to a Denial of Service
(unkillable tasks in `D` state). There is no memory corruption, use-after-free,
or out-of-bounds access involved.
* **Denial Of Service:** True. The hung tasks will trigger the `khungtaskd`
panic (if `panic_on_hung_task` is set) or simply leave unkillable processes
holding critical filesystem and memory locks (`mmap_lock`, `sb_writers`),
effectively hanging the system or the affected mount point.
* **Accessible From Unprivileged Processes & User Namespaces:** False. Creating
user-space block devices (like `/dev/nbd0`, `/dev/loop-control`, or
`/dev/raw-gadget`) requires root privileges (mode 0600, owned by root).
Furthermore, mounting an `ext4` filesystem is not permitted in unprivileged user
namespaces (`FS_USERNS_MOUNT` is not set for ext4).
* **Peripheral Trigger:** True. An attacker could physically plug in a malicious
USB mass storage device that advertises a valid partition table but then
intentionally ignores all subsequent SCSI read/write commands and bus resets. If
the system auto-mounts the device, the kernel will hang waiting for the IO to
complete, resulting in a DoS.
* **Filesystem Trigger:** False. The hang is caused by the block device failing
to complete IO requests, not by the filesystem parsing malicious data
structures. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/06/01 14:11 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/06/01 14:11 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/0a2d2406965b48ddaf344179001bc441683a7b09]
|
| 3/1 |
2026/06/01 14:11 |
action |
kernel-builder |
29m
Results: map[KernelObj:/app/workdir/cache/build/3055a588309eb882ee4fd38652bad0c7f8d71914]
|
| 4/1 |
2026/06/01 14:41 |
action |
codesearch-prepare |
21m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/06/01 15:03 |
agent |
expert |
5m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Instruction: You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by grepping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completely wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control transfers, that also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidential Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
INFO: task kworker/u32:2:46 blocked in I/O wait for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u32:2 state:D stack:24840 pid:46 tgid:46 ppid:2 task_flags:0x4248160 flags:0x00080000
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
do_get_write_access+0x84f/0x1220 fs/jbd2/transaction.c:1113
jbd2_journal_get_write_access+0x1d6/0x280 fs/jbd2/transaction.c:1263
__ext4_journal_get_write_access+0x6a/0x340 fs/ext4/ext4_jbd2.c:241
ext4_mb_mark_context+0x179/0xdb0 fs/ext4/mballoc.c:4111
ext4_mb_mark_diskspace_used+0x472/0x800 fs/ext4/mballoc.c:4240
ext4_mb_new_blocks+0x93d/0x4c60 fs/ext4/mballoc.c:6328
ext4_ext_map_blocks+0x1c74/0x5930 fs/ext4/extents.c:4461
ext4_map_create_blocks+0xec/0x5e0 fs/ext4/inode.c:631
ext4_map_blocks+0x46b/0xd30 fs/ext4/inode.c:824
mpage_map_one_extent fs/ext4/inode.c:2396 [inline]
mpage_map_and_submit_extent fs/ext4/inode.c:2490 [inline]
ext4_do_writepages+0x2313/0x3f20 fs/ext4/inode.c:2948
ext4_writepages+0x347/0x790 fs/ext4/inode.c:3042
do_writepages+0x278/0x600 mm/page-writeback.c:2571
__writeback_single_inode+0x164/0x1350 fs/fs-writeback.c:1764
writeback_sb_inodes+0x766/0x1c60 fs/fs-writeback.c:2056
__writeback_inodes_wb+0xf8/0x2d0 fs/fs-writeback.c:2132
wb_writeback+0x720/0xb90 fs/fs-writeback.c:2243
wb_check_old_data_flush fs/fs-writeback.c:2347 [inline]
wb_do_writeback fs/fs-writeback.c:2400 [inline]
wb_workfn+0x8dd/0xc00 fs/fs-writeback.c:2428
process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
process_scheduled_works kernel/workqueue.c:3397 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
INFO: task jbd2/sda1-8:5110 blocked in I/O wait for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:jbd2/sda1-8 state:D stack:25720 pid:5110 tgid:5110 ppid:2 task_flags:0x240040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
__wait_on_buffer+0x64/0x70 fs/buffer.c:123
wait_on_buffer include/linux/buffer_head.h:420 [inline]
jbd2_journal_commit_transaction+0x388a/0x6870 fs/jbd2/commit.c:837
kjournald2+0x200/0x760 fs/jbd2/journal.c:201
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
INFO: task syz.2.343:7067 blocked in I/O wait for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.343 state:D stack:26216 pid:7067 tgid:7067 ppid:5740 task_flags:0x440040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
do_get_write_access+0x84f/0x1220 fs/jbd2/transaction.c:1113
jbd2_journal_get_write_access+0x1d6/0x280 fs/jbd2/transaction.c:1263
__ext4_journal_get_write_access+0x6a/0x340 fs/ext4/ext4_jbd2.c:241
ext4_reserve_inode_write+0x1b7/0x330 fs/ext4/inode.c:6375
__ext4_mark_inode_dirty+0x18f/0x890 fs/ext4/inode.c:6550
ext4_dirty_inode+0xd9/0x130 fs/ext4/inode.c:6587
__mark_inode_dirty+0x1f3/0x1720 fs/fs-writeback.c:2623
generic_update_time fs/inode.c:2198 [inline]
touch_atime+0x642/0x7a0 fs/inode.c:2273
file_accessed include/linux/fs.h:2264 [inline]
ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
vfs_mmap_prepare include/linux/fs.h:2076 [inline]
call_mmap_prepare mm/vma.c:2672 [inline]
__mmap_region+0xe98/0x2dd0 mm/vma.c:2755
mmap_region+0x527/0x620 mm/vma.c:2857
do_mmap+0xc63/0x12f0 mm/mmap.c:560
vm_mmap_pgoff+0x29e/0x470 mm/util.c:581
ksys_mmap_pgoff+0x3cb/0x610 mm/mmap.c:606
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
__x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd8c239cbc2
RSP: 002b:00007ffc17417508 EFLAGS: 00000206 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000001b33364000 RCX: 00007fd8c239cbc2
RDX: 0000000000000003 RSI: 00000000003c0000 RDI: 0000001b33364000
RBP: 0000000000100001 R08: 0000000000000004 R09: 0000000000040000
R10: 0000000000100001 R11: 0000000000000206 R12: 0000000000000058
R13: 00000000000927c0 R14: 000000000001357c R15: 00007ffc174177e0
</TASK>
INFO: task syz.1.344:7068 blocked in I/O wait for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.344 state:D stack:27600 pid:7068 tgid:7068 ppid:5743 task_flags:0x440040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
do_get_write_access+0x84f/0x1220 fs/jbd2/transaction.c:1113
jbd2_journal_get_write_access+0x1d6/0x280 fs/jbd2/transaction.c:1263
__ext4_journal_get_write_access+0x6a/0x340 fs/ext4/ext4_jbd2.c:241
ext4_reserve_inode_write+0x1b7/0x330 fs/ext4/inode.c:6375
__ext4_mark_inode_dirty+0x18f/0x890 fs/ext4/inode.c:6550
ext4_dirty_inode+0xd9/0x130 fs/ext4/inode.c:6587
__mark_inode_dirty+0x1f3/0x1720 fs/fs-writeback.c:2623
generic_update_time fs/inode.c:2198 [inline]
touch_atime+0x642/0x7a0 fs/inode.c:2273
file_accessed include/linux/fs.h:2264 [inline]
ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
vfs_mmap_prepare include/linux/fs.h:2076 [inline]
call_mmap_prepare mm/vma.c:2672 [inline]
__mmap_region+0xe98/0x2dd0 mm/vma.c:2755
mmap_region+0x527/0x620 mm/vma.c:2857
do_mmap+0xc63/0x12f0 mm/mmap.c:560
vm_mmap_pgoff+0x29e/0x470 mm/util.c:581
ksys_mmap_pgoff+0x3cb/0x610 mm/mmap.c:606
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
__x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7a3c99cbc2
RSP: 002b:00007ffde6352238 EFLAGS: 00000206 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000001b33264000 RCX: 00007f7a3c99cbc2
RDX: 0000000000000003 RSI: 00000000003c0000 RDI: 0000001b33264000
RBP: 0000000000100001 R08: 0000000000000004 R09: 0000000000040000
R10: 0000000000100001 R11: 0000000000000206 R12: 000000000000003f
R13: 00000000000927c0 R14: 000000000001368d R15: 00007ffde6352510
</TASK>
INFO: task syz.3.345:7069 blocked in I/O wait for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.3.345 state:D stack:27600 pid:7069 tgid:7069 ppid:5745 task_flags:0x440040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
do_get_write_access+0x84f/0x1220 fs/jbd2/transaction.c:1113
jbd2_journal_get_write_access+0x1d6/0x280 fs/jbd2/transaction.c:1263
__ext4_journal_get_write_access+0x6a/0x340 fs/ext4/ext4_jbd2.c:241
ext4_reserve_inode_write+0x1b7/0x330 fs/ext4/inode.c:6375
__ext4_mark_inode_dirty+0x18f/0x890 fs/ext4/inode.c:6550
ext4_dirty_inode+0xd9/0x130 fs/ext4/inode.c:6587
__mark_inode_dirty+0x1f3/0x1720 fs/fs-writeback.c:2623
generic_update_time fs/inode.c:2198 [inline]
touch_atime+0x642/0x7a0 fs/inode.c:2273
file_accessed include/linux/fs.h:2264 [inline]
ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
vfs_mmap_prepare include/linux/fs.h:2076 [inline]
call_mmap_prepare mm/vma.c:2672 [inline]
__mmap_region+0xe98/0x2dd0 mm/vma.c:2755
mmap_region+0x527/0x620 mm/vma.c:2857
do_mmap+0xc63/0x12f0 mm/mmap.c:560
vm_mmap_pgoff+0x29e/0x470 mm/util.c:581
ksys_mmap_pgoff+0x3cb/0x610 mm/mmap.c:606
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
__x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f470679cbc2
RSP: 002b:00007ffea3648948 EFLAGS: 00000206 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 0000001b33464000 RCX: 00007f470679cbc2
RDX: 0000000000000003 RSI: 00000000003c0000 RDI: 0000001b33464000
RBP: 0000000000100001 R08: 0000000000000004 R09: 0000000000040000
R10: 0000000000100001 R11: 0000000000000206 R12: 000000000000005d
R13: 00000000000927c0 R14: 000000000001325f R15: 00007ffea3648c20
</TASK>
INFO: task syz.0.346:7070 blocked in I/O wait for more than 144 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.346 state:D stack:28456 pid:7070 tgid:7070 ppid:5737 task_flags:0x440040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5388 [inline]
__schedule+0x1295/0x67a0 kernel/sched/core.c:7189
__schedule_loop kernel/sched/core.c:7268 [inline]
schedule+0xdd/0x390 kernel/sched/core.c:7283
io_schedule+0x8a/0xf0 kernel/sched/core.c:8110
bit_wait_io+0xd/0xe0 kernel/sched/wait_bit.c:250
__wait_on_bit+0x65/0x180 kernel/sched/wait_bit.c:52
out_of_line_wait_on_bit+0xdc/0x110 kernel/sched/wait_bit.c:67
wait_on_bit_io include/linux/wait_bit.h:105 [inline]
do_get_write_access+0x84f/0x1220 fs/jbd2/transaction.c:1113
jbd2_journal_get_write_access+0x1d6/0x280 fs/jbd2/transaction.c:1263
__ext4_journal_get_write_access+0x6a/0x340 fs/ext4/ext4_jbd2.c:241
ext4_reserve_inode_write+0x1b7/0x330 fs/ext4/inode.c:6375
__ext4_mark_inode_dirty+0x18f/0x890 fs/ext4/inode.c:6550
ext4_dirty_inode+0xd9/0x130 fs/ext4/inode.c:6587
__mark_inode_dirty+0x1f3/0x1720 fs/fs-writeback.c:2623
generic_update_time fs/inode.c:2198 [inline]
file_update_time_flags+0x46b/0x500 fs/inode.c:2428
ext4_page_mkwrite+0x324/0x1890 fs/ext4/inode.c:6753
do_page_mkwrite+0x17a/0x440 mm/memory.c:3684
do_shared_fault mm/memory.c:5985 [inline]
do_fault+0x3b5/0x1750 mm/memory.c:6047
do_pte_missing mm/memory.c:4566 [inline]
handle_pte_fault mm/memory.c:6427 [inline]
__handle_mm_fault+0x187d/0x2a00 mm/memory.c:6565
handle_mm_fault+0x37b/0xa30 mm/memory.c:6734
do_user_addr_fault+0x5a3/0x12f0 arch/x86/mm/fault.c:1334
handle_page_fault arch/x86/mm/fault.c:1474 [inline]
exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1527
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7f915106a903
RSP: 002b:00007ffdfe1654d0 EFLAGS: 00010246
RAX: 000000000003fde8 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000001b33124000 RSI: 0000000000040000 RDI: 00007f91513db710
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffdfe165760
</TASK>
Showing all locks held in the system:
1 lock held by khungtaskd/41:
#0: ffffffff8e7e5620 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e7e5620 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
#0: ffffffff8e7e5620 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
6 locks held by kworker/u32:2/46:
#0: ffff88801d355940 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3289
#1: ffffc900007efd08 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3290
#2: ffff88802d08e0d8 (&type->s_umount_key#55){++++}-{4:4}, at: super_trylock_shared+0x1e/0xf0 fs/super.c:565
#3: ffff888038abcc18 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0x278/0x600 mm/page-writeback.c:2571
#4: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
#5: ffff888040909e18 (&ei->i_data_sem){++++}-{4:4}, at: ext4_map_blocks+0x45a/0xd30 fs/ext4/inode.c:823
2 locks held by kworker/u33:1/5098:
#0: ffff888029225140 ((wq_completion)nbd1-recv){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3289
#1: ffffc90027097d08 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3290
2 locks held by getty/5540:
#0: ffff888038ab30a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc900033732e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14f0 drivers/tty/n_tty.c:2211
3 locks held by syz-executor/5649:
#0: ffff88801b8d3438 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:611 [inline]
#0: ffff88801b8d3438 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline]
#0: ffff88801b8d3438 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x35/0x6f0 mm/mmap_lock.c:501
#1: ffff88802d08e508 (sb_pagefaults){.+.+}-{0:0}, at: do_page_mkwrite+0x17a/0x440 mm/memory.c:3684
#2: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
2 locks held by kworker/u33:2/5739:
#0: ffff888029225140 ((wq_completion)nbd1-recv){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3289
#1: ffffc90003e4fd08 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3290
2 locks held by kworker/u33:6/5751:
#0: ffff888029225140 ((wq_completion)nbd1-recv){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3289
#1: ffffc90003e6fd08 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3290
3 locks held by syz.2.343/7067:
#0: ffff8880402527f8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
#0: ffff8880402527f8 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:579
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2264 [inline]
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
#2: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
3 locks held by syz.1.344/7068:
#0: ffff888022cf4078 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
#0: ffff888022cf4078 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:579
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2264 [inline]
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
#2: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
3 locks held by syz.3.345/7069:
#0: ffff88802efd4cb8 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
#0: ffff88802efd4cb8 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:579
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2264 [inline]
#1: ffff88802d08e410 (sb_writers#5){.+.+}-{0:0}, at: ext4_file_mmap_prepare+0x56d/0x670 fs/ext4/file.c:840
#2: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
3 locks held by syz.0.346/7070:
#0: ffff88803518b5c8 (vm_lock){++++}-{0:0}, at: lock_vma_under_rcu+0x11d/0x590 mm/mmap_lock.c:310
#1: ffff88802d08e508 (sb_pagefaults){.+.+}-{0:0}, at: do_page_mkwrite+0x17a/0x440 mm/memory.c:3684
#2: ffff888038aba938 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfaa/0x13a0 fs/jbd2/transaction.c:444
=============================================
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 41 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
nmi_cpu_backtrace.cold+0x12d/0x151 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x1d7/0x230 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
__sys_info lib/sys_info.c:157 [inline]
sys_info+0x141/0x190 lib/sys_info.c:165
check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
watchdog+0xcb1/0x1030 kernel/hung_task.c:561
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 1 to CPUs 0,2-3:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
Code: 95 94 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 03 41 24 00 fb f4 <e9> fc 43 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffffff8e407e00 EFLAGS: 00000206
RAX: 000000000013f5f3 RBX: ffffffff8e4955c0 RCX: ffffffff8b875285
RDX: 0000000000000000 RSI: ffffffff8df0b1c4 RDI: ffffffff8c1c4480
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed100d4867b5
R10: ffff88806a433dab R11: 0000000000000000 R12: 0000000000000000
R13: fffffbfff1c92ab8 R14: 0000000000000000 R15: ffffffff90d6d350
FS: 0000000000000000(0000) GS:ffff8880d6390000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055fd179a8660 CR3: 000000000e596000 CR4: 0000000000352ef0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
default_idle+0x9/0x10 arch/x86/kernel/process.c:767
default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x464/0x590 kernel/sched/idle.c:352
cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
rest_init+0x251/0x260 init/main.c:762
start_kernel+0x484/0x490 init/main.c:1220
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x148
</TASK>
NMI backtrace for cpu 3
CPU: 3 UID: 0 PID: 0 Comm: swapper/3 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
Code: 95 94 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 03 41 24 00 fb f4 <e9> fc 43 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000197df0 EFLAGS: 00000206
RAX: 00000000000c497d RBX: ffff88801eac2540 RCX: ffffffff8b875285
RDX: 0000000000000000 RSI: ffffffff8df0b1c4 RDI: ffffffff8c1c4480
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed100d4e67b5
R10: ffff88806a733dab R11: 0000000000000000 R12: 0000000000000003
R13: ffffed1003d584a8 R14: 0000000000000003 R15: ffffffff90d6d350
FS: 0000000000000000(0000) GS:ffff8880d6690000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055fd179a7028 CR3: 000000000e596000 CR4: 0000000000352ef0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
default_idle+0x9/0x10 arch/x86/kernel/process.c:767
default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x464/0x590 kernel/sched/idle.c:352
cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x148
</TASK>
NMI backtrace for cpu 2
CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
Code: 95 94 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 03 41 24 00 fb f4 <e9> fc 43 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000187df0 EFLAGS: 00000206
RAX: 0000000000148bdb RBX: ffff88801eac4a80 RCX: ffffffff8b875285
RDX: 0000000000000000 RSI: ffffffff8df0b1c4 RDI: ffffffff8c1c4480
RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed100d4c67b5
R10: ffff88806a633dab R11: 0000000000000000 R12: 0000000000000002
R13: ffffed1003d58950 R14: 0000000000000002 R15: ffffffff90d6d350
FS: 0000000000000000(0000) GS:ffff8880d6590000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055fd179a8660 CR3: 000000002d5a7000 CR4: 0000000000352ef0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
default_idle+0x9/0x10 arch/x86/kernel/process.c:767
default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x464/0x590 kernel/sched/idle.c:352
cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x148
</TASK>
----------------
Code disassembly (best guess):
0: 95 xchg %eax,%ebp
1: 94 xchg %eax,%esp
2: 02 c3 add %bl,%al
4: cc int3
5: cc int3
6: cc int3
7: cc int3
8: 0f 1f 00 nopl (%rax)
b: 90 nop
c: 90 nop
d: 90 nop
e: 90 nop
f: 90 nop
10: 90 nop
11: 90 nop
12: 90 nop
13: 90 nop
14: 90 nop
15: 90 nop
16: 90 nop
17: 90 nop
18: 90 nop
19: 90 nop
1a: 90 nop
1b: f3 0f 1e fa endbr64
1f: eb 07 jmp 0x28
21: 0f 00 2d 03 41 24 00 verw 0x244103(%rip) # 0x24412b
28: fb sti
29: f4 hlt
* 2a: e9 fc 43 03 00 jmp 0x3442b <-- trapping instruction
2f: 66 2e 0f 1f 84 00 00 cs nopw 0x0(%rax,%rax,1)
36: 00 00 00
39: 66 90 xchg %ax,%ax
3b: 90 nop
3c: 90 nop
3d: 90 nop
3e: 90 nop
3f: 90 nop
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the issue:
**Root Cause Analysis:**
The bug report shows several tasks hung in `D` state for over 143 seconds.
1. The `jbd2/sda1-8` thread (the journal commit thread for the `sda1` ext4 filesystem) is blocked in `wait_on_buffer()` within `jbd2_journal_commit_transaction()`. It has submitted a metadata buffer to the block layer via `submit_bh()` and is waiting for the block IO to complete (which clears the `BH_Lock` bit).
2. Other tasks (`syz.*` and `kworker`) are blocked in `do_get_write_access()` waiting for the `BH_Shadow` bit to be cleared on a buffer. This bit is cleared by `journal_end_buffer_io_sync()` when the block IO for the committing transaction completes.
This indicates a complete block IO stall on the `sda1` block device. The block layer is not completing the submitted bios.
The presence of `nbd1-recv` workers in the lockdep output strongly suggests that syzkaller has set up a user-space block device (like NBD, or a USB mass storage device via `/dev/raw-gadget` backed by NBD/loop). If the user-space process responsible for handling the IO for this block device (e.g., the syzkaller NBD server or USB gadget emulator) stops responding, hangs, or intentionally sleeps, the block IO will hang indefinitely. The kernel's block layer and the SCSI error handler (which can also hang or loop if the device ignores resets) will wait for the device, causing the filesystem mounted on it to hang.
This is a known and expected behavior when dealing with user-space emulated block devices or failing hardware. The kernel cannot magically complete IO if the underlying device or user-space emulator refuses to respond.
**Security Impact Assessment:**
* **Exploitable:** False. This is a pure IO hang leading to a Denial of Service (unkillable tasks in `D` state). There is no memory corruption, use-after-free, or out-of-bounds access involved.
* **Denial Of Service:** True. The hung tasks will trigger the `khungtaskd` panic (if `panic_on_hung_task` is set) or simply leave unkillable processes holding critical filesystem and memory locks (`mmap_lock`, `sb_writers`), effectively hanging the system or the affected mount point.
* **Accessible From Unprivileged Processes & User Namespaces:** False. Creating user-space block devices (like `/dev/nbd0`, `/dev/loop-control`, or `/dev/raw-gadget`) requires root privileges (mode 0600, owned by root). Furthermore, mounting an `ext4` filesystem is not permitted in unprivileged user namespaces (`FS_USERNS_MOUNT` is not set for ext4).
* **Peripheral Trigger:** True. An attacker could physically plug in a malicious USB mass storage device that advertises a valid partition table but then intentionally ignores all subsequent SCSI read/write commands and bus resets. If the system auto-mounts the device, the kernel will hang waiting for the IO to complete, resulting in a DoS.
* **Filesystem Trigger:** False. The hang is caused by the block device failing to complete IO requests, not by the filesystem parsing malicious data structures.
|
| 6/2 |
2026/06/01 15:03 |
llm |
expert |
0m
Model:
Tokens:
input: 19878
output: 34
thoughts: 642
Thoughts: **Analyzing a Suspected ext4/jbd2 Deadlock**
Okay, so I've got this hung task report. Immediately, a few tasks jump out: `kworker`, `jbd2`, and a `syz` process, all blocked in I/O wait for a significant amount of time β over 143 seconds, to be precise. The common thread here is the kernel code: they're all tangled up in `ext4` and `jbd2` operations. That's my initial red flag.
Diving deeper into the call stacks, `kworker` appears to be writing back data, calling `ext4_mb_mark_diskspace_used`, and eventually getting into `jbd2_journal_get_write_access`, leading to `wait_on_bit_io`. The `jbd2` thread itself, `jbd2/sda1-8`, is within the `jbd2_journal_commit_transaction` function, and it's blocked by `wait_on_buffer`. Now, that's interesting because the first task is in that function as well.
The `syz` process also ends up in the same critical part of the code, after operations that also lead into the journal. Page fault or mmap leads to these situations too.
I'm starting to see a pattern: these tasks are contending for access to the journal, and it looks like `jbd2_journal_commit_transaction` is the bottleneck, specifically that `wait_on_buffer` call. It's highly suggestive of a deadlock or at least a very long wait condition within the journal operations. I need to take a closer look at the `jbd2_journal_commit_transaction` function around line 837 to see what's happening. I need to understand what buffer the `jbd2` thread is waiting on and why these threads are stuck at that point in code.
|
| 7/2 |
2026/06/01 15:03 |
tool |
grepper |
0m
Args: map[Expression:wait_on_buffer PathPrefix:fs/jbd2/commit.c]
Results: map[Output:fs/jbd2/commit.c=165=static int journal_wait_on_commit_record(journal_t *journal,
--
fs/jbd2/commit.c-170- clear_buffer_dirty(bh);
fs/jbd2/commit.c:171: wait_on_buffer(bh);
fs/jbd2/commit.c-172-
--
fs/jbd2/commit.c=377=void jbd2_journal_commit_transaction(journal_t *journal)
--
fs/jbd2/commit.c-836-
fs/jbd2/commit.c:837: wait_on_buffer(bh);
fs/jbd2/commit.c-838- cond_resched();
--
fs/jbd2/commit.c-879- bh = list_entry(log_bufs.prev, struct buffer_head, b_assoc_buffers);
fs/jbd2/commit.c:880: wait_on_buffer(bh);
fs/jbd2/commit.c-881- cond_resched();
]
|
| 8/2 |
2026/06/01 15:03 |
llm |
expert |
0m
Model:
Tokens:
input: 21259
output: 38
thoughts: 41
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of kernel debugging:
**Diving into the JBD2 Transaction Commit**
Alright, so the error message points me squarely at line 837 in `jbd2_journal_commit_transaction`. That immediately tells me where the problem *likely* lies β within the commit process of the JBD2 journaling file system. Now, let's open up `fs/jbd2/commit.c` and get right to that area of the code. I need to understand what's happening at or around that specific line. My guess is there's some kind of data integrity issue or race condition during the finalization of the journal transaction. Let's see what's being done at that point and analyze the surrounding logic to understand the potential failure point.
|
| 9/2 |
2026/06/01 15:03 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/commit.c FirstLine:800 LineCount:100]
Results: map[Contents: 800: * If the journal is not located on the file system device,
801: * then we must flush the file system device before we issue
802: * the commit record and update the journal tail sequence.
803: */
804: if ((commit_transaction->t_need_data_flush || update_tail) &&
805: (journal->j_fs_dev != journal->j_dev) &&
806: (journal->j_flags & JBD2_BARRIER))
807: blkdev_issue_flush(journal->j_fs_dev);
808:
809: /* Done it all: now write the commit record asynchronously. */
810: if (jbd2_has_feature_async_commit(journal)) {
811: err = journal_submit_commit_record(journal, commit_transaction,
812: &cbh, crc32_sum);
813: if (err)
814: jbd2_journal_abort(journal, err);
815: }
816:
817: blk_finish_plug(&plug);
818:
819: /* Lo and behold: we have just managed to send a transaction to
820: the log. Before we can commit it, wait for the IO so far to
821: complete. Control buffers being written are on the
822: transaction's t_log_list queue, and metadata buffers are on
823: the io_bufs list.
824:
825: Wait for the buffers in reverse order. That way we are
826: less likely to be woken up until all IOs have completed, and
827: so we incur less scheduling load.
828: */
829:
830: jbd2_debug(3, "JBD2: commit phase 3\n");
831:
832: while (!list_empty(&io_bufs)) {
833: struct buffer_head *bh = list_entry(io_bufs.prev,
834: struct buffer_head,
835: b_assoc_buffers);
836:
837: wait_on_buffer(bh);
838: cond_resched();
839:
840: if (unlikely(!buffer_uptodate(bh)))
841: err = -EIO;
842: jbd2_unfile_log_bh(bh);
843: stats.run.rs_blocks_logged++;
844:
845: /*
846: * The list contains temporary buffer heads created by
847: * jbd2_journal_write_metadata_buffer().
848: */
849: BUFFER_TRACE(bh, "dumping temporary bh");
850: __brelse(bh);
851: J_ASSERT_BH(bh, atomic_read(&bh->b_count) == 0);
852: free_buffer_head(bh);
853:
854: /* We also have to refile the corresponding shadowed buffer */
855: jh = commit_transaction->t_shadow_list->b_tprev;
856: bh = jh2bh(jh);
857: clear_buffer_jwrite(bh);
858: J_ASSERT_BH(bh, buffer_jbddirty(bh));
859: J_ASSERT_BH(bh, !buffer_shadow(bh));
860:
861: /* The metadata is now released for reuse, but we need
862: to remember it against this transaction so that when
863: we finally commit, we can do any checkpointing
864: required. */
865: JBUFFER_TRACE(jh, "file as BJ_Forget");
866: jbd2_journal_file_buffer(jh, commit_transaction, BJ_Forget);
867: JBUFFER_TRACE(jh, "brelse shadowed buffer");
868: __brelse(bh);
869: }
870:
871: J_ASSERT (commit_transaction->t_shadow_list == NULL);
872:
873: jbd2_debug(3, "JBD2: commit phase 4\n");
874:
875: /* Here we wait for the revoke record and descriptor record buffers */
876: while (!list_empty(&log_bufs)) {
877: struct buffer_head *bh;
878:
879: bh = list_entry(log_bufs.prev, struct buffer_head, b_assoc_buffers);
880: wait_on_buffer(bh);
881: cond_resched();
882:
883: if (unlikely(!buffer_uptodate(bh)))
884: err = -EIO;
885:
886: BUFFER_TRACE(bh, "ph5: control buffer writeout done: unfile");
887: clear_buffer_jwrite(bh);
888: jbd2_unfile_log_bh(bh);
889: stats.run.rs_blocks_logged++;
890: __brelse(bh); /* One for getblk */
891: /* AKPM: bforget here */
892: }
893:
894: if (err)
895: jbd2_journal_abort(journal, err);
896:
897: jbd2_debug(3, "JBD2: commit phase 5\n");
898: write_lock(&journal->j_state_lock);
899: J_ASSERT(commit_transaction->t_state == T_COMMIT_DFLUSH);
]
|
| 10/2 |
2026/06/01 15:03 |
llm |
expert |
0m
Model:
Tokens:
input: 23143
output: 36
thoughts: 556
Thoughts: **Analyzing a Hanging IO Situation**
Okay, so I'm looking at this `jbd2` thread, and it's blocked, waiting for I/O to complete on a buffer head. Annoying. The immediate question is always *why* isn't this I/O finishing? Let's dig into this. I'll check what other threads are active on the system.
I see `kworker/u33:1/5098`, `kworker/u33:2/5739`, and `kworker/u33:6/5751`. Hmm, these are `nbd1-recv` workers. *NBD*? That's a potential red flag. This suggests the filesystem might be mounted on a Network Block Device. If the NBD server is dead or unresponsive, I/O to that block device will just hang indefinitely.
Let's quickly check the lock situation for one of those NBD workers. I see two locks held by `kworker/u33:1/5098`. This seems normal for a workqueue.
If the filesystem is on NBD and the NBD server is a syzkaller process that crashed, then IO to the filesystem will stall.
Wait, the bug report says `jbd2/sda1-8` is blocked. The device being written to is `sda1`. Okay, so `jbd2` is on `sda1`, not `nbd1`. That rules out the immediate NBD server being dead.
`sda1` is a partition on `sda`. So, is there an NBD device involved *at all*? The `nbd1-recv` workers might just be running in the background.
Let's look more closely at that `syz.0.346:7070` process, the one mentioned in the bug report that seems to be hanging in `do_page_mkwrite`. It's waiting on `do_get_write_access` -> `wait_on_bit_io`. Looks like `do_get_write_access` is blocking on something, waiting for the buffer to unlock. I'll need to check the exact function in the source to understand this fully. Time to look at `fs/jbd2/transaction.c:1113`.
|
| 11/2 |
2026/06/01 15:03 |
tool |
grepper |
0m
Args: map[Expression:do_get_write_access PathPrefix:fs/jbd2/transaction.c]
Results: map[Output:fs/jbd2/transaction.c=947=static int
fs/jbd2/transaction.c:948:do_get_write_access(handle_t *handle, struct journal_head *jh,
fs/jbd2/transaction.c-949- int force_copy)
--
fs/jbd2/transaction.c=1169=static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh,
--
fs/jbd2/transaction.c-1209- * doesn't get reordered and see inconsistent state of concurrent
fs/jbd2/transaction.c:1210: * do_get_write_access().
fs/jbd2/transaction.c-1211- */
--
fs/jbd2/transaction.c=1233=int jbd2_journal_get_write_access(handle_t *handle, struct buffer_head *bh)
--
fs/jbd2/transaction.c-1262- * completes any outstanding IO before proceeding. */
fs/jbd2/transaction.c:1263: rc = do_get_write_access(handle, jh, 0);
fs/jbd2/transaction.c-1264- jbd2_journal_put_journal_head(jh);
--
fs/jbd2/transaction.c=1401=int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
--
fs/jbd2/transaction.c-1420- */
fs/jbd2/transaction.c:1421: err = do_get_write_access(handle, jh, 1);
fs/jbd2/transaction.c-1422- if (err)
--
fs/jbd2/transaction.c=2132=static void __jbd2_journal_unfile_buffer(struct journal_head *jh)
--
fs/jbd2/transaction.c-2167- * Who else is affected by this? hmm... Really the only contender
fs/jbd2/transaction.c:2168: * is do_get_write_access() - it could be looking at the buffer while
fs/jbd2/transaction.c-2169- * journal_try_to_free_buffer() is changing its state. But that
--
fs/jbd2/transaction.c=2531=void __jbd2_journal_file_buffer(struct journal_head *jh,
--
fs/jbd2/transaction.c-2552- * instead of buffer_dirty. We should not see a dirty bit set
fs/jbd2/transaction.c:2553: * here because we clear it in do_get_write_access but e.g.
fs/jbd2/transaction.c-2554- * tune2fs can modify the sb and set the dirty bit at any time
]
|
| 12/2 |
2026/06/01 15:03 |
llm |
expert |
0m
Model:
Tokens:
input: 24988
output: 39
thoughts: 22
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person:
**Diving into `fs/jbd2/transaction.c` β Line 1113**
Okay, time to dig into the guts of JBD2 again. I'm focusing on the transaction handling within the journaling filesystem, and line 1113 in `fs/jbd2/transaction.c` seems like a likely point of interest. I'm guessing it's probably involved with either committing a transaction, handling the buffer head list, or dealing with some crucial aspect of the metadata management. Given my understanding of the likely structure of the jbd2 codebase, I'm expecting to find a conditional statement or a function call to a critical sub-routine related to either flushing or logging data. It could be something related to block allocation, metadata updates, or potentially handling journal recovery after a crash. Let's see what the code at that location reveals. I'm expecting to either validate my assumptions or be pleasantly surprised by something I haven't considered.
|
| 13/2 |
2026/06/01 15:04 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/transaction.c FirstLine:1080 LineCount:100]
Results: map[Contents:1080: spin_unlock(&jh->b_state_lock);
1081: error = -EINVAL;
1082: jbd2_journal_abort(journal, error);
1083: goto out;
1084: }
1085: goto attach_next;
1086: }
1087:
1088: JBUFFER_TRACE(jh, "owned by older transaction");
1089: if (WARN_ON_ONCE(jh->b_next_transaction ||
1090: jh->b_transaction !=
1091: journal->j_committing_transaction)) {
1092: pr_err("JBD2: %s: assertion failure: b_next_transaction=%p b_transaction=%p j_committing_transaction=%p\n",
1093: journal->j_devname, jh->b_next_transaction,
1094: jh->b_transaction, journal->j_committing_transaction);
1095: spin_unlock(&jh->b_state_lock);
1096: error = -EINVAL;
1097: jbd2_journal_abort(journal, error);
1098: goto out;
1099: }
1100:
1101: /*
1102: * There is one case we have to be very careful about. If the
1103: * committing transaction is currently writing this buffer out to disk
1104: * and has NOT made a copy-out, then we cannot modify the buffer
1105: * contents at all right now. The essence of copy-out is that it is
1106: * the extra copy, not the primary copy, which gets journaled. If the
1107: * primary copy is already going to disk then we cannot do copy-out
1108: * here.
1109: */
1110: if (buffer_shadow(bh)) {
1111: JBUFFER_TRACE(jh, "on shadow: sleep");
1112: spin_unlock(&jh->b_state_lock);
1113: wait_on_bit_io(&bh->b_state, BH_Shadow, TASK_UNINTERRUPTIBLE);
1114: goto repeat;
1115: }
1116:
1117: /*
1118: * Only do the copy if the currently-owning transaction still needs it.
1119: * If buffer isn't on BJ_Metadata list, the committing transaction is
1120: * past that stage (here we use the fact that BH_Shadow is set under
1121: * bh_state lock together with refiling to BJ_Shadow list and at this
1122: * point we know the buffer doesn't have BH_Shadow set).
1123: *
1124: * Subtle point, though: if this is a get_undo_access, then we will be
1125: * relying on the frozen_data to contain the new value of the
1126: * committed_data record after the transaction, so we HAVE to force the
1127: * frozen_data copy in that case.
1128: */
1129: if (jh->b_jlist == BJ_Metadata || force_copy) {
1130: JBUFFER_TRACE(jh, "generate frozen data");
1131: if (!frozen_buffer) {
1132: JBUFFER_TRACE(jh, "allocate memory for buffer");
1133: spin_unlock(&jh->b_state_lock);
1134: frozen_buffer = jbd2_alloc(jh2bh(jh)->b_size,
1135: GFP_NOFS | __GFP_NOFAIL);
1136: goto repeat;
1137: }
1138: jh->b_frozen_data = frozen_buffer;
1139: frozen_buffer = NULL;
1140: jbd2_freeze_jh_data(jh);
1141: }
1142: attach_next:
1143: /*
1144: * Make sure all stores to jh (b_modified, b_frozen_data) are visible
1145: * before attaching it to the running transaction. Paired with barrier
1146: * in jbd2_write_access_granted()
1147: */
1148: smp_wmb();
1149: jh->b_next_transaction = transaction;
1150:
1151: done:
1152: spin_unlock(&jh->b_state_lock);
1153:
1154: /*
1155: * If we are about to journal a buffer, then any revoke pending on it is
1156: * no longer valid
1157: */
1158: jbd2_journal_cancel_revoke(handle, jh);
1159:
1160: out:
1161: if (unlikely(frozen_buffer)) /* It's usually NULL */
1162: jbd2_free(frozen_buffer, bh->b_size);
1163:
1164: JBUFFER_TRACE(jh, "exit");
1165: return error;
1166: }
1167:
1168: /* Fast check whether buffer is already attached to the required transaction */
1169: static bool jbd2_write_access_granted(handle_t *handle, struct buffer_head *bh,
1170: bool undo)
1171: {
1172: struct journal_head *jh;
1173: bool ret = false;
1174:
1175: /* Dirty buffers require special handling... */
1176: if (buffer_dirty(bh))
1177: return false;
1178:
1179: /*
]
|
| 14/2 |
2026/06/01 15:04 |
llm |
expert |
0m
Model:
Tokens:
input: 26855
output: 38
thoughts: 1748
Thoughts: **Analyzing a Potential Filesystem Deadlock**
Okay, so I'm looking at this deadlock scenario and trying to piece together what's happening. My initial observation is that `do_get_write_access` seems to be waiting on the `BH_Shadow` bit, while `jbd2_journal_commit_transaction` is stuck on `wait_on_buffer(bh)`. This means the commit process is waiting for a buffer's `BH_Lock` to clear. Typically, the IO subsystem holds this lock during a write. If IO is stuck, the lock never clears, and we have a problem.
The block device in question is `sda1`. The bug report indicates tasks like `jbd2/sda1-8`, `kworker/u32:2`, and a `syz.*` process are blocked in I/O. That "I/O wait" is the key. I wonder, is there any other process holding a lock and blocking the commiting process?
I see that `nbd1-recv` (an NBD workqueue) has a couple of locks. Hmmm, could there be a connection? Is `sda1` somehow linked to `nbd1`? Syzkaller often uses loop devices or even NBD devices backed by files. A key question: is `sda1` the root filesystem? If the NBD server is writing to a file on `sda1`, or if a loop device is creating contention for the disk, this is a distinct possibility. If the NBD server is memory-mapping IO it could page fault and block on the `sda1` journal. This block would propogate to NBD IO then the filesystem.
The hung tasks waiting on `sda1` suggest the journal is the bottleneck. The `jbd2_journal_commit_transaction`'s `wait_on_buffer(bh)` indicates it's submitted a buffer for writing and is waiting for the block layer to complete it. Why might a write to `sda1` not finish? Is the QEMU disk full? Is there a block layer deadlock?
Now, I'm examining the locks held by a `syz-executor` process. It's holding `jbd2_handle`, `sb_pagefaults`, and `mmap_lock`. Wait, other syzkaller tasks are also holding the `jbd2_handle`! This suggests they're all part of the *same* transaction! The transaction needs all these handles to be dropped. `jbd2_journal_commit_transaction` only waits on buffers *after* it's changed the transaction state to commit *and* waited for all handles to drop. This implies the root cause is that the transaction is not completing, as evidenced by a backlog of handles. It's time to dig deeper into `fs/jbd2/commit.c` to understand the exact commit process.
|
| 15/2 |
2026/06/01 15:04 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/commit.c FirstLine:400 LineCount:100]
Results: map[Contents: 400: /* Tail of the journal */
401: unsigned long first_block;
402: tid_t first_tid;
403: int update_tail;
404: int csum_size = 0;
405: LIST_HEAD(io_bufs);
406: LIST_HEAD(log_bufs);
407:
408: if (jbd2_journal_has_csum_v2or3(journal))
409: csum_size = sizeof(struct jbd2_journal_block_tail);
410:
411: /*
412: * First job: lock down the current transaction and wait for
413: * all outstanding updates to complete.
414: */
415:
416: /* Do we need to erase the effects of a prior jbd2_journal_flush? */
417: if (journal->j_flags & JBD2_FLUSHED) {
418: jbd2_debug(3, "super block updated\n");
419: mutex_lock_io(&journal->j_checkpoint_mutex);
420: /*
421: * We hold j_checkpoint_mutex so tail cannot change under us.
422: * We don't need any special data guarantees for writing sb
423: * since journal is empty and it is ok for write to be
424: * flushed only with transaction commit.
425: */
426: jbd2_journal_update_sb_log_tail(journal,
427: journal->j_tail_sequence,
428: journal->j_tail, 0);
429: mutex_unlock(&journal->j_checkpoint_mutex);
430: } else {
431: jbd2_debug(3, "superblock not updated\n");
432: }
433:
434: J_ASSERT(journal->j_running_transaction != NULL);
435: J_ASSERT(journal->j_committing_transaction == NULL);
436:
437: write_lock(&journal->j_state_lock);
438: journal->j_flags |= JBD2_FULL_COMMIT_ONGOING;
439: while (journal->j_flags & JBD2_FAST_COMMIT_ONGOING) {
440: DEFINE_WAIT(wait);
441:
442: prepare_to_wait(&journal->j_fc_wait, &wait,
443: TASK_UNINTERRUPTIBLE);
444: write_unlock(&journal->j_state_lock);
445: schedule();
446: write_lock(&journal->j_state_lock);
447: finish_wait(&journal->j_fc_wait, &wait);
448: /*
449: * TODO: by blocking fast commits here, we are increasing
450: * fsync() latency slightly. Strictly speaking, we don't need
451: * to block fast commits until the transaction enters T_FLUSH
452: * state. So an optimization is possible where we block new fast
453: * commits here and wait for existing ones to complete
454: * just before we enter T_FLUSH. That way, the existing fast
455: * commits and this full commit can proceed parallely.
456: */
457: }
458: write_unlock(&journal->j_state_lock);
459:
460: commit_transaction = journal->j_running_transaction;
461:
462: trace_jbd2_start_commit(journal, commit_transaction);
463: jbd2_debug(1, "JBD2: starting commit of transaction %d\n",
464: commit_transaction->t_tid);
465:
466: write_lock(&journal->j_state_lock);
467: journal->j_fc_off = 0;
468: J_ASSERT(commit_transaction->t_state == T_RUNNING);
469: commit_transaction->t_state = T_LOCKED;
470:
471: trace_jbd2_commit_locking(journal, commit_transaction);
472: stats.run.rs_wait = commit_transaction->t_max_wait;
473: stats.run.rs_request_delay = 0;
474: stats.run.rs_locked = jiffies;
475: if (commit_transaction->t_requested)
476: stats.run.rs_request_delay =
477: jbd2_time_diff(commit_transaction->t_requested,
478: stats.run.rs_locked);
479: stats.run.rs_running = jbd2_time_diff(commit_transaction->t_start,
480: stats.run.rs_locked);
481:
482: // waits for any t_updates to finish
483: jbd2_journal_wait_updates(journal);
484:
485: commit_transaction->t_state = T_SWITCH;
486:
487: J_ASSERT (atomic_read(&commit_transaction->t_outstanding_credits) <=
488: journal->j_max_transaction_buffers);
489:
490: /*
491: * First thing we are allowed to do is to discard any remaining
492: * BJ_Reserved buffers. Note, it is _not_ permissible to assume
493: * that there are no such buffers: if a large filesystem
494: * operation like a truncate needs to split itself over multiple
495: * transactions, then it may try to do a jbd2_journal_restart() while
496: * there are still BJ_Reserved buffers outstanding. These must
497: * be released cleanly from the current transaction.
498: *
499: * In this case, the filesystem must still reserve write access
]
|
| 16/2 |
2026/06/01 15:04 |
llm |
expert |
0m
Model:
Tokens:
input: 30943
output: 27
thoughts: 1747
Thoughts: **Analyzing a Possible Ext4 IO Hang in a Syzkaller VM**
Okay, so here's what I'm thinking. We've got this `jbd2_journal_wait_updates()` call and the system is hung. The core issue is that IO isn't completing. Let's break this down.
Firstly, `jbd2_journal_wait_updates()` suggests the committing transaction has finished waiting for handles to be dropped. The tasks are waiting on `wait_on_bit_io` within `do_get_write_access`, so they are *already* holding a handle and part of the *running* transaction, *not* the one committing. The committing transaction is in the `T_COMMIT` state and it is waiting for `wait_on_buffer(bh)` to finish the write.
Specifically, `syz.0.346:7070` holds a handle for the *running* transaction and it's blocked in `do_get_write_access`, waiting for `BH_Shadow` to be cleared. The committing transaction sets `BH_Shadow` when writing the buffer to disk. So, we're seeing a normal waiting scenario, where the running transaction is waiting for the prior one to finish IO. The problem, as usual, is the IO isn't completing.
The workers `kworker/u33:1/5098`, `kworker/u33:2/5739`, `kworker/u33:6/5751` are executing `nbd1-recv`. This indicates an active NBD device `nbd1`. The question is if `sda1` is somehow mapped or related to `nbd1`. Syzkaller often uses NBD devices. But the `jbd2` thread is named `jbd2/sda1-8`, not `jbd2/nbd1-8`.
Now, if `sda1` *is* the root filesystem, which is typical for syzkaller, we've got an IO problem on the root filesystem. The question that remains is *why* the IO is hanging on `/dev/sda1`. CPUs are mostly idle, so we're not deadlocked on CPU.
Looking at the held locks, it doesn't immediately reveal a clear deadlock scenario. What's interesting is if `nbd1` is involved.
Could syzkaller have used a "flakey" DM mapping from `sda1` to `nbd1`? No. But is `nbd1` being used as a backing device for something else that somehow writes to `sda1`? If an NBD server is writing to a file on `sda1`, and the server needs to complete its IO before the root filesystem finishes committing a transaction, that might block it. But this seems unlikely; the NBD server's IO would be independent.
So then, what if QEMU's disk is full or paused? If QEMU is paused, `khungtaskd` wouldn't be running. So QEMU is running, making me think it's not a VM-level issue, rather something *inside* the VM.
Looking at the tasks in D state, we've got `kworker/u32:2:46` doing `wb_workfn` -> `ext4_writepages` -> `ext4_mb_new_blocks`. Could `sda1` be a USB mass storage device in this case, rather than the typical SCSI disk in QEMU? No, `sda` is usually the first SCSI disk.
Could a loop device be involved, set up with `ioctl(fd, LOOP_SET_FD, ...)`? If `sda1` is indeed a root device, it seems less likely that a loop device would cause the root filesystem IO to hang. The `nbd` workers aren't in D state, so they are not the problem.
Wait, what if `sda1` *isn't* the root filesystem? Syzkaller *can* create a disk image, attach it via USB, and it gets named `sda1` if the root filesystem is `vda`. In many setups the root filesystem is `/dev/vda1`, and `/dev/sda` is a syzkaller created USB or SCSI device!
**The critical question now is what the actual root filesystem is. Time to check the kernel config or command line.**
|
| 17/2 |
2026/06/01 15:04 |
tool |
grepper |
0m
Error:
Args: map[Expression:CONFIG_CMDLINE= PathPrefix:.config]
Results:
|
| 18/2 |
2026/06/01 15:04 |
llm |
expert |
0m
Model:
Tokens:
input: 33688
output: 24
thoughts: 39
Thoughts: Okay, here's my interpretation of those thoughts, summarized from my perspective as an expert:
**Investigating Potential Root Filesystem Location**
Alright, so the situation is I need to figure out where the root filesystem resides, but I'm operating under the constraint that I *don't* have direct access to the kernel command line at the moment. My initial inclination, naturally, would be to simply grep the command line output for the `root=` parameter. That's usually the most straightforward way to determine the device being used. But since that's off the table, I need a good workaround. It seems that I can check if the `vda` block device is in use, and use that as the basis of my assumption. This sounds like a solid starting point given the restriction!
|
| 19/2 |
2026/06/01 15:04 |
tool |
grepper |
0m
Args: map[Expression:/dev/root PathPrefix:]
Results: map[Output:Documentation/admin-guide/devices.rst=112=exist, they should have the following uses.
--
Documentation/admin-guide/devices.rst-119-/dev/modem modem port symbolic Current dialout device
Documentation/admin-guide/devices.rst:120:/dev/root root device symbolic Current root filesystem
Documentation/admin-guide/devices.rst-121-/dev/swap swap device symbolic Current swap device
--
Documentation/admin-guide/devices.txt-150-
Documentation/admin-guide/devices.txt:151: 0 = /dev/root
Documentation/admin-guide/devices.txt-152-
--
Documentation/filesystems/proc.rst=1967=This file contains lines of the form::
Documentation/filesystems/proc.rst-1968-
Documentation/filesystems/proc.rst:1969: 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
Documentation/filesystems/proc.rst-1970- (1)(2)(3) (4) (5) (6) (nβ¦m) (m+1)(m+2) (m+3) (m+4)
--
fs/btrfs/volumes.c=1407=static bool btrfs_skip_registration(struct btrfs_super_block *disk_super,
--
fs/btrfs/volumes.c-1415- * maj:min but different paths. Booting without initrd relies on
fs/btrfs/volumes.c:1416: * /dev/root initially, later replaced with the actual root device.
fs/btrfs/volumes.c-1417- * A successful scan ensures grub2-probe selects the correct device.
--
init/do_mounts.c=368=static void __init mount_block_root(char *root_device_name)
init/do_mounts.c-369-{
init/do_mounts.c:370: int err = create_dev("/dev/root", ROOT_DEV);
init/do_mounts.c-371-
init/do_mounts.c-372- if (err < 0)
init/do_mounts.c:373: pr_emerg("Failed to create /dev/root: %d\n", err);
init/do_mounts.c:374: mount_root_generic("/dev/root", root_device_name, root_mountflags);
init/do_mounts.c-375-}
]
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| 20/2 |
2026/06/01 15:04 |
llm |
expert |
0m
Model:
Tokens:
input: 34586
output: 32
thoughts: 2479
Thoughts: **My Analysis of the Hung Task Scenario**
Okay, here's how I'm thinking through this, given the information:
1. My initial thought is that `sda1` is a USB mass storage device. This seems likely, given Syzkaller's capabilities. If this is the case, Syzkaller *could* inject malicious USB traffic, simulating a disk that simply stops responding to read/write requests. This would cause `wait_on_buffer(bh)` within `jbd2_journal_commit_transaction` to hang. I verify that Syzkaller indeed has `syz_usb_connect`, allowing for USB mass storage emulation. A filesystem mounted on the emulated USB device will cause SCSI commands to hang if the syzkaller process then stops answering requests. This is a potential vulnerability.
2. My next step is to consider timeouts. SCSI commands typically *have* timeouts. If the SCSI error handler, when invoked due to a timeout, also hangs, or if the timeout is infinite, the system is deadlocked. However, if it's a USB mass storage device, maybe USB subsystem handles the timeout. I confirm there's no evidence of timeouts being a factor from the stack traces. The stack traces point to waiting on the block layer directly.
3. I explore other possible scenarios for `sda1` hanging - loop device, NBD device, fault injection, and the rootfs - but these seem less likely given that the hung tasks are specifically waiting on buffer completion related to block device operations.
4. I pivot and consider an iSCSI device, but conclude that Syzkaller does not normally set up iSCSI targets.
5. Then, I consider NBD specifically. The `lockdep` output is key here, specifically the mention of `nbd1-recv`. This *strongly* suggests that `nbd1` is active. I theorize if `sda1` could be a loop device backed by a file on `nbd1`. That's not right since loop devices get their own names, but it does make me look at NBD devices.
6. I check if `sda` could be an iSCSI device. I remember that the iSCSI server can be Syzkaller, which might stop responding, causing IO to `sda` to hang. Since I know Syzkaller has some network fuzzing I rule it out, and that's not it.
7. I look deeper into NBD. I realize `nbd1` could be created by Syzkaller using a USB mass storage device (`sda`) and a backing file on `nbd1`. So, Syzkaller sets up `nbd1`, then a USB mass storage gadget backed by `/dev/nbd1`. The kernel enumerates `sda`, finds `sda1`, mounts it as ext4, and does filesystem operations, which send IO through the stack: SCSI -> USB -> dummy\_hcd -> USB gadget -> read/write to `/dev/nbd1`.
8. This IO chain points out that if the NBD server hangs, then so does the entire IO path. Specifically:
1. Syzkaller sets up `nbd1`.
2. Syzkaller sets up a USB mass storage gadget, backed by `/dev/nbd1` or a file on it.
3. The dummy\_hcd connects the gadget to the host (which is the same kernel).
4. The kernel enumerates a new SCSI device, `sda`.
5. The kernel reads the partition table, finds `sda1`.
6. Syzkaller mounts `/dev/sda1` as ext4.
7. Syzkaller does some filesystem operations, which generate IO to `sda1`.
8. The IO to `sda1` goes through SCSI -> USB -> dummy\_hcd -> USB gadget -> read/write to `/dev/nbd1`.
9. The read/write to `/dev/nbd1` goes to the NBD server.
10. If the NBD server (a syzkaller process) hangs or is killed, the IO to `nbd1` hangs.
11. The USB gadget IO hangs.
12. The SCSI IO hangs.
13. The ext4/jbd2 IO hangs.
14. `khungtaskd` detects the hung tasks.
9. I verify that `g_mass_storage` can indeed be backed by a block device such as `/dev/nbd1`, using the `file=` parameter.
10. I then look at the state of `nbd1-recv` to determine why it's not present in the hung task list. The
|
| 21/2 |
2026/06/01 15:05 |
tool |
grepper |
0m
Args: map[Expression:submit_bh PathPrefix:fs/jbd2/commit.c]
Results: map[Output:fs/jbd2/commit.c=114=static int journal_submit_commit_record(journal_t *journal,
--
fs/jbd2/commit.c-155-
fs/jbd2/commit.c:156: submit_bh(write_flags, bh);
fs/jbd2/commit.c-157- *cbh = bh;
--
fs/jbd2/commit.c=377=void jbd2_journal_commit_transaction(journal_t *journal)
--
fs/jbd2/commit.c-754- bh->b_end_io = journal_end_buffer_io_sync;
fs/jbd2/commit.c:755: submit_bh(REQ_OP_WRITE | JBD2_JOURNAL_REQ_FLAGS,
fs/jbd2/commit.c-756- bh);
]
|
| 22/2 |
2026/06/01 15:05 |
llm |
expert |
0m
Model:
Tokens:
input: 38356
output: 38
thoughts: 22
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into the JBD2 Commit Process**
Okay, time to get to the heart of the matter. I need to understand how the journaling block device (JBD2) handles commits. I'm going to focus on `fs/jbd2/commit.c`, specifically around line 754. That seems like a reasonable point to start investigating the commit path. I'm assuming that the commit logic, perhaps the crucial synchronization point or some critical data structure update, is likely handled near this region, or at the very least, a call to a function that performs such an operation. From here, I can examine the surrounding code to determine how that logic is called and connected to the other structures of the file system. Let's see what we can find.
|
| 23/2 |
2026/06/01 15:05 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/commit.c FirstLine:700 LineCount:100]
Results: map[Contents: 700: if (escape)
701: tag_flag |= JBD2_FLAG_ESCAPE;
702: if (!first_tag)
703: tag_flag |= JBD2_FLAG_SAME_UUID;
704:
705: tag = (journal_block_tag_t *) tagp;
706: write_tag_block(journal, tag, jh2bh(jh)->b_blocknr);
707: tag->t_flags = cpu_to_be16(tag_flag);
708: jbd2_block_tag_csum_set(journal, tag, wbuf[bufs],
709: commit_transaction->t_tid);
710: tagp += tag_bytes;
711: space_left -= tag_bytes;
712: bufs++;
713:
714: if (first_tag) {
715: memcpy (tagp, journal->j_uuid, 16);
716: tagp += 16;
717: space_left -= 16;
718: first_tag = 0;
719: }
720:
721: /* If there's no more to do, or if the descriptor is full,
722: let the IO rip! */
723:
724: if (bufs == journal->j_wbufsize ||
725: commit_transaction->t_buffers == NULL ||
726: space_left < tag_bytes + 16 + csum_size) {
727:
728: jbd2_debug(4, "JBD2: Submit %d IOs\n", bufs);
729:
730: /* Write an end-of-descriptor marker before
731: submitting the IOs. "tag" still points to
732: the last tag we set up. */
733:
734: tag->t_flags |= cpu_to_be16(JBD2_FLAG_LAST_TAG);
735: start_journal_io:
736: if (descriptor)
737: jbd2_descriptor_block_csum_set(journal,
738: descriptor);
739:
740: for (i = 0; i < bufs; i++) {
741: struct buffer_head *bh = wbuf[i];
742:
743: /*
744: * Compute checksum.
745: */
746: if (jbd2_has_feature_checksum(journal)) {
747: crc32_sum =
748: jbd2_checksum_data(crc32_sum, bh);
749: }
750:
751: lock_buffer(bh);
752: clear_buffer_dirty(bh);
753: set_buffer_uptodate(bh);
754: bh->b_end_io = journal_end_buffer_io_sync;
755: submit_bh(REQ_OP_WRITE | JBD2_JOURNAL_REQ_FLAGS,
756: bh);
757: }
758: cond_resched();
759:
760: /* Force a new descriptor to be generated next
761: time round the loop. */
762: descriptor = NULL;
763: bufs = 0;
764: }
765: }
766:
767: err = journal_finish_inode_data_buffers(journal, commit_transaction);
768: if (err) {
769: printk(KERN_WARNING
770: "JBD2: Detected IO errors %d while flushing file data on %s\n",
771: err, journal->j_devname);
772: err = 0;
773: }
774:
775: /*
776: * Get current oldest transaction in the log before we issue flush
777: * to the filesystem device. After the flush we can be sure that
778: * blocks of all older transactions are checkpointed to persistent
779: * storage and we will be safe to update journal start in the
780: * superblock with the numbers we get here.
781: */
782: update_tail =
783: jbd2_journal_get_log_tail(journal, &first_tid, &first_block);
784:
785: write_lock(&journal->j_state_lock);
786: if (update_tail) {
787: long freed = first_block - journal->j_tail;
788:
789: if (first_block < journal->j_tail)
790: freed += journal->j_last - journal->j_first;
791: /* Update tail only if we free significant amount of space */
792: if (freed < journal->j_max_transaction_buffers)
793: update_tail = 0;
794: }
795: J_ASSERT(commit_transaction->t_state == T_COMMIT);
796: commit_transaction->t_state = T_COMMIT_DFLUSH;
797: write_unlock(&journal->j_state_lock);
798:
799: /*
]
|
| 24/2 |
2026/06/01 15:05 |
llm |
expert |
0m
Model:
Tokens:
input: 40126
output: 33
thoughts: 704
Thoughts: **Analyzing a Block Device Hang**
Okay, so I'm looking at this hang. The process submits buffers using `submit_bh` and then waits on them with `wait_on_buffer(bh)`. The `end_io` function, `journal_end_buffer_io_sync`, is supposed to unlock the buffer after the I/O completes. The problem is, if the block device *never* completes the I/O, `journal_end_buffer_io_sync` is never called, and `wait_on_buffer` just hangs. Classic block device hang, right?
The next question is, why is the block device hanging? Let's trace this back. Could it be a problem with a `loop` device? Say syzkaller creates a loop device backed by a file on `/dev/sda1`, mounts ext4 on `loop0`, and then does I/O. That I/O goes to `loop0`, which writes to the file on `/dev/sda1`, which in turn involves `/dev/sda1`'s ext4. If `loop0`'s ext4 is committing, it sends I/O to `loop0`. The `loop0` thread then receives the bio and writes to the backing file on `/dev/sda1` using `vfs_write`. Now, if `/dev/sda1`'s ext4 is *also* committing, it could potentially block. I see where this is going... if `/dev/sda1` is blocked, then `loop0` is blocked.
But wait, the hung task is actually `jbd2/sda1-8`. That's the jbd2 thread for `/dev/sda1`, not `loop0`. So, the problem is `/dev/sda1` itself. Why is `/dev/sda1` hanging?
Okay, think about what syzkaller can do. Is `/dev/sda1` actually the root file system? No. It's likely a device created by syzkaller. Syzkaller can create a USB mass storage device, a loop device, or an NBD device. If it's a USB mass storage device, it gets named `sda` (if root is `vda`, for example). A loop device would be `loop0`, and an NBD device would be `nbd0`. Since the hung task is `jbd2/sda1-8`, the device must be `/dev/sda1`.
So, if the root file system is `/dev/sda1`, then syzkaller is running on `/dev/sda1`. But if the root file system is `vda1`, then `/dev/sda1` must be a USB mass storage device that syzkaller created.
Let me check if syzkaller creates USB mass storage devices. Yes, I knew it! Syzkaller has `syz_usb_connect` and `syz_usb_connect_ath9k` and so on. So syzkaller *can* create USB mass storage devices! And if syzkaller creates the USB mass storage device, it has full control over the backing implementation because it emulates the USB device in user-space using `/dev/raw-gadget` or dummy_hcd.
Aha! Now I see. Syzkaller is reading USB requests from `/dev/raw-gadget` and sending responses. If the syzkaller process *stops* reading requests or sending responses, the USB mass storage driver will hang, waiting for the device! The SCSI command should time out, but maybe the USB mass storage error handler also hangs, or it takes a very long time, or it's not able to abort the command?
Alright, let's take a look at the USB storage driver code under `drivers/usb/storage/`. This is where the issue must lie.
|
| 25/2 |
2026/06/01 15:05 |
tool |
grepper |
0m
Args: map[Expression:usb_stor_port_reset PathPrefix:drivers/usb/storage/]
Results: map[Output:drivers/usb/storage/scsiglue.c=475=static int bus_reset(struct scsi_cmnd *srb)
--
drivers/usb/storage/scsiglue.c-481-
drivers/usb/storage/scsiglue.c:482: result = usb_stor_port_reset(us);
drivers/usb/storage/scsiglue.c-483- return result < 0 ? FAILED : SUCCESS;
--
drivers/usb/storage/transport.c=604=void usb_stor_invoke_transport(struct scsi_cmnd *srb, struct us_data *us)
--
drivers/usb/storage/transport.c-918- mutex_unlock(&us->dev_mutex);
drivers/usb/storage/transport.c:919: result = usb_stor_port_reset(us);
drivers/usb/storage/transport.c-920- mutex_lock(&us->dev_mutex);
--
drivers/usb/storage/transport.c=1431=EXPORT_SYMBOL_GPL(usb_stor_Bulk_reset);
--
drivers/usb/storage/transport.c-1436- */
drivers/usb/storage/transport.c:1437:int usb_stor_port_reset(struct us_data *us)
drivers/usb/storage/transport.c-1438-{
--
drivers/usb/storage/transport.h=84=extern int usb_stor_bulk_srb(struct us_data* us, unsigned int pipe,
--
drivers/usb/storage/transport.h-86-
drivers/usb/storage/transport.h:87:extern int usb_stor_port_reset(struct us_data *us);
drivers/usb/storage/transport.h-88-#endif
]
|
| 26/2 |
2026/06/01 15:05 |
llm |
expert |
0m
Model:
Tokens:
input: 42137
output: 31
thoughts: 3847
Thoughts: **Analyzing a Kernel Hang in Syzkaller: A Deep Dive**
Okay, so I'm looking at this kernel hang in the syzkaller environment, trying to figure out what's causing the IO to stall. The initial clues point to a USB device, specifically, a SCSI command timing out. The error handler gets triggered, but it seems to get stuck, which is why IO is not completing and why `wait_on_buffer` isn't waking up. The bug report doesn't flag `scsi_eh` as hung, but maybe it is stuck in an uninterruptible sleep state (`D`). It's not in `D` state, and the timeout is likely the usual SCSI timeout of 30 seconds, not a larger value.
The task involved is `jbd2/sda1-8`. This is the first question - is `sda1` the root filesystem? It isn't a typical NBD, loop, or device mapper device naming convention. It has to be a SCSI disk partition. How can a SCSI disk partition hang? There are a few scenarios:
1. It's a USB mass storage device emulated by syzkaller.
2. It's an iSCSI device emulated by syzkaller.
3. Or, the root filesystem is involved, and QEMU is somehow hanging the IO.
If QEMU is hanging the IO, it's probably because the host disk is full, which is a common problem in syzkaller. The infrastructure usually prevents this, but it can still happen. Or, maybe syzkaller is injecting faults to block IO? Fault injection usually returns errors and doesn't block. What about userfaultfd on a memory-mapped file on `sda1`? This could cause blocking, but, let's look at the tasks and their locks.
`syz.0.346:7070` is blocked, waiting for the committing transaction, holding `vm_lock`, `sb_pagefaults`, `jbd2_handle`. `jbd2/sda1-8:5110` is doing the committing, holding the `BH_Lock` bit to be cleared by the block IO completion.
`syz.2.343:7067` is also blocked on the same commit. `kworker/u32:2:46` is another worker thread blocked on the same transaction. So, everyone is blocked on `jbd2/sda1-8`. The block IO is not completing! If `sda1` is the root filesystem, this means the QEMU block device isn't completing IO.
Could an NBD server be involved? Let's check the NBD worker threads, `kworker/u33:1/5098`, `kworker/u33:2/5739`, and `kworker/u33:6/5751`. Yes, they are NBD workers! Could there be a loop device or device mapper involved? Probably not, since the task is `sda1`. Syzkaller might be creating an NBD device and naming it `sda1`, but this is highly unlikely. The root filesystem also can't just be mounted over NBD.
Okay, so maybe `sda1` is just the root filesystem, and a block layer bug is causing hangs when NBD is used. But what about that NBD device, if it's the backing file for another NBD device or loop device? That wouldn't hang `sda1`. What if the NBD server is writing to `sda1`? The NBD server could block, but that shouldn't impact the transaction commit on `sda1`. Unless, `sda1` is a USB mass storage device, and its backing file is on `nbd1`!
Here's the chain:
1. Syzkaller creates an NBD device `nbd1`.
2. Syzkaller creates a USB mass storage gadget (`g_mass_storage`) backed by `/dev/nbd1`.
3. The kernel enumerates the USB device as `sda`.
4. The kernel reads the partition, finds `sda1`.
5. Syzkaller mounts `/dev/sda1`.
6. Syzkaller does some operations that trigger a transaction commit.
7. `jbd2/sda1-8` submits a write bio to `sda1`.
8. The bio goes to `sda1` -> USB mass storage -> `g_mass_storage` thread.
9. `g_mass_storage` does a synchronous write to `/dev/nbd1`.
10. The write to `/dev/nbd
|
| 27/2 |
2026/06/01 15:06 |
tool |
grepper |
0m
Args: map[Expression:raw_gadget PathPrefix:drivers/usb/gadget/]
Results: map[Output:drivers/usb/gadget/legacy/Kconfig=516=config USB_RAW_GADGET
--
drivers/usb/gadget/legacy/Kconfig-529- Say "y" to link the driver statically, or "m" to build a
drivers/usb/gadget/legacy/Kconfig:530: dynamically linked module called "raw_gadget".
drivers/usb/gadget/legacy/Kconfig-531-
--
drivers/usb/gadget/legacy/Makefile=45=obj-$(CONFIG_USB_GADGET_TARGET) += tcm_usb_gadget.o
drivers/usb/gadget/legacy/Makefile:46:obj-$(CONFIG_USB_RAW_GADGET) += raw_gadget.o
--
drivers/usb/gadget/legacy/raw_gadget.c-29-
drivers/usb/gadget/legacy/raw_gadget.c:30:#include <uapi/linux/usb/raw_gadget.h>
drivers/usb/gadget/legacy/raw_gadget.c-31-
]
|
| 28/2 |
2026/06/01 15:06 |
llm |
expert |
0m
Model:
Tokens:
input: 47314
output: 38
thoughts: 15
Thoughts: Okay, let's dive into this. Here's how I'd approach that snippet, as though it were my own thought process:
**Diving into `raw_gadget.c` for Permission Scrutiny**
Alright, before we go any further down this particular rabbit hole, the first thing that jumps out at me is that we need to scrutinize `raw_gadget.c` for any potential permission-related vulnerabilities. We're dealing with low-level gadgetry, so permissions are absolutely critical. It's almost guaranteed there will be some interplay with the kernel, and the implications of misconfigured permissions at this stage could be catastrophic. I need to figure out exactly which calls are being made, what they're accessing, and under what context they're operating.
I'm thinking: *file permissions, capabilities, DACs, MACs... are we talking userland, kernel space, or a mix?* I have to keep the entire permission landscape in my head and navigate it. I also need to be on the lookout for implicit assumptions about privilege. If the code *assumes* it's running with certain permissions, then that's a red flag. I want to see if they're being checked and verified throughout the program. This should be interesting to check the system calls used.
Essentially, I want to map out the entire permission graph associated with this piece of code to gain confidence and ensure a safe implementation.
|
| 29/2 |
2026/06/01 15:06 |
tool |
grepper |
0m
Args: map[Expression:raw_open PathPrefix:drivers/usb/gadget/legacy/raw_gadget.c]
Results: map[Output:drivers/usb/gadget/legacy/raw_gadget.c=425=static struct miscdevice raw_misc_device;
drivers/usb/gadget/legacy/raw_gadget.c-426-
drivers/usb/gadget/legacy/raw_gadget.c:427:static int raw_open(struct inode *inode, struct file *fd)
drivers/usb/gadget/legacy/raw_gadget.c-428-{
--
drivers/usb/gadget/legacy/raw_gadget.c=444=static int raw_release(struct inode *inode, struct file *fd)
--
drivers/usb/gadget/legacy/raw_gadget.c-472-out_put:
drivers/usb/gadget/legacy/raw_gadget.c:473: /* Matches dev_new() in raw_open(). */
drivers/usb/gadget/legacy/raw_gadget.c-474- kref_put(&dev->count, dev_free);
--
drivers/usb/gadget/legacy/raw_gadget.c=1363=static const struct file_operations raw_fops = {
drivers/usb/gadget/legacy/raw_gadget.c:1364: .open = raw_open,
drivers/usb/gadget/legacy/raw_gadget.c-1365- .unlocked_ioctl = raw_ioctl,
]
|
| 30/2 |
2026/06/01 15:06 |
llm |
expert |
0m
Model:
Tokens:
input: 48029
output: 43
thoughts: 9
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Initial Assessment: Navigating the Landscape**
Alright, the initial prompt is simple: "Let's read `raw_open`." No fuss, no embellishment. The implication is clear, and I'm ready to dive in. There's an expectation that I already know the context, the codebase, or the problem domain where `raw_open` resides. It's a call to action, a signal to engage with a specific, likely crucial, piece of code or a concept. I instantly start framing the problem β what am I expecting to see in this `raw_open`? Is this a low-level file handler? A wrapper around something? Is it custom or standard? Is it intended for handling binary data, or text? My initial thought process is geared toward establishing expectations and anticipating potential complexities before I start reading. The level of detail Iβll focus on will depend on the problemβs urgency and my existing familiarity with the area.
|
| 31/2 |
2026/06/01 15:06 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/legacy/raw_gadget.c FirstLine:420 LineCount:50]
Results: map[Contents: 420: dev_err(&gadget->dev, "failed to queue reset event\n");
421: }
422:
423: /*----------------------------------------------------------------------*/
424:
425: static struct miscdevice raw_misc_device;
426:
427: static int raw_open(struct inode *inode, struct file *fd)
428: {
429: struct raw_dev *dev;
430:
431: /* Nonblocking I/O is not supported yet. */
432: if (fd->f_flags & O_NONBLOCK)
433: return -EINVAL;
434:
435: dev = dev_new();
436: if (!dev)
437: return -ENOMEM;
438: fd->private_data = dev;
439: dev->state = STATE_DEV_OPENED;
440: dev->dev = raw_misc_device.this_device;
441: return 0;
442: }
443:
444: static int raw_release(struct inode *inode, struct file *fd)
445: {
446: int ret = 0;
447: struct raw_dev *dev = fd->private_data;
448: unsigned long flags;
449: bool unregister = false;
450:
451: spin_lock_irqsave(&dev->lock, flags);
452: dev->state = STATE_DEV_CLOSED;
453: if (!dev->gadget) {
454: spin_unlock_irqrestore(&dev->lock, flags);
455: goto out_put;
456: }
457: if (dev->gadget_registered)
458: unregister = true;
459: dev->gadget_registered = false;
460: spin_unlock_irqrestore(&dev->lock, flags);
461:
462: if (unregister) {
463: ret = usb_gadget_unregister_driver(&dev->driver);
464: if (ret != 0)
465: dev_err(dev->dev,
466: "usb_gadget_unregister_driver() failed with %d\n",
467: ret);
468: /* Matches kref_get() in raw_ioctl_run(). */
469: kref_put(&dev->count, dev_free);
]
|
| 32/2 |
2026/06/01 15:06 |
llm |
expert |
0m
Model:
Tokens:
input: 49029
output: 44
thoughts: 42
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing as an expert:
**Analyzing the `raw_open` Vulnerability Landscape**
Right, so I'm thinking about this `raw_open` function. It seems there's a potential blind spot β it's not performing any capability checks. That's a red flag, classic one too. The thing is, this device, `/dev/raw-gadget`, is brought into existence via a `misc_register` call. That makes me wonder what's happening at that point. I need to dig into `raw_misc_device` to see if there's any pre-emptive authorization. I want to see if this is being handled earlier in the process because the `raw_open` itself doesn't seem to be doing any of that work. That might give me a direction to investigate further.
|
| 33/2 |
2026/06/01 15:06 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/legacy/raw_gadget.c FirstLine:1360 LineCount:50]
Results: map[Contents:1360:
1361: /*----------------------------------------------------------------------*/
1362:
1363: static const struct file_operations raw_fops = {
1364: .open = raw_open,
1365: .unlocked_ioctl = raw_ioctl,
1366: .compat_ioctl = raw_ioctl,
1367: .release = raw_release,
1368: };
1369:
1370: static struct miscdevice raw_misc_device = {
1371: .minor = MISC_DYNAMIC_MINOR,
1372: .name = DRIVER_NAME,
1373: .fops = &raw_fops,
1374: };
1375:
1376: module_misc_device(raw_misc_device);
]
|
| 34/2 |
2026/06/01 15:06 |
llm |
expert |
0m
Model:
Tokens:
input: 49545
output: 36
thoughts: 1100
Thoughts: **Analyzing a Potential Syzkaller-Triggered Hang**
Okay, let's break this down. My initial thought is that `miscdevice` defaults to restrictive permissions, so an unprivileged user can't normally interact with `/dev/raw-gadget`. But wait, syzkaller, being what it is, runs tests as root, or within a user namespace where it could potentially have access if itβs bind-mounted, or the executor opens it before dropping privileges. Ah yes, the syzkaller executor does run as root and does open `/dev/raw-gadget` for the test process, which is how it can trigger this.
So, is this a security vulnerability? If root causes a deadlock, it's generally not seen as one, since root can do anything. But if an unprivileged user could do it, that's a different story. Can they create a loop device? No, `/dev/loop-control` is usually root-only. NBD? Nope, `/dev/nbdX` is also root-protected. FUSE, though? Ah, yes, unprivileged users can, assuming `fusermount` is available and setuid, or through user namespaces.
Now, if an unprivileged user sets up a FUSE mount, creates a file, and then tries to get a privileged process or the kernel to write to that file while holding a lock, and the FUSE server blocks the write... we have a potential deadlock. This is a known FUSE issue, and the kernel has tried to address these FUSE deadlocks, but they still exist.
But wait, in this bug report, the hung task is `jbd2/sda1-8`. This is the journal thread for `sda1`, an ext4 filesystem. If `sda1` is the root filesystem, and the FUSE server is writing to it. The key issue is that when the FUSE server writes to `sda1`, it doesn't hold locks, it just does a normal write. If `sda1` is committing a transaction, the write might block, but that shouldn't deadlock the commit! The `sda1` commit is waiting for IO completion to `sda1`, handled by the block device, e.g., QEMU virtio-blk. The block device isn't dependent on the FUSE server, so the commit will complete, and the FUSE server will unblock. No deadlock there!
So why the hang? Because the block device *is* dependent on syzkaller! This means `sda1` is not the root filesystem, or its block device is dependent on syzkaller, which is impossible since syzkaller runs inside the VM. Therefore, `sda1` must be a block device created by syzkaller. If syzkaller created it, it can hang it. If syzkaller makes it hang, the `jbd2` thread for that device hangs. And that's our hung task warning.
Is this a kernel bug? If a userspace process emulates a block device (NBD, raw-gadget, loop), and that process hangs, the block device will hang. This is expected behavior. The kernel's block and filesystem layers will wait for the IO to complete. The kernel can't magically complete the IO if the device is dead. Wait, shouldn't there be a timeout and the IO aborted? NBD does have a timeout; if the server doesn't respond, the driver can timeout and return `-EIO`. But syzkaller might have configured NBD without a timeout, or a long timeout. USB mass storage has a SCSI timeout (30 seconds), but the SCSI error handler tries to reset the device. If the raw-gadget device doesn't respond to the reset, the error handler could hang or eventually offline the device. If it offlines the device, the IO should complete with `-EIO`.
So why after 143 seconds didn't it complete with `-EIO`? Maybe there's a bug in the USB raw-gadget driver that doesn't handle resets properly, causing the SCSI error handler to hang? I need to check if `scsi_eh` (SCSI error handler) is hung. If it's hung, it would be in a `D` state. Let me search the kernel source for `scsi_eh` to see what it waits on.
|
| 35/2 |
2026/06/01 15:06 |
tool |
grepper |
0m
Args: map[Expression:wait_for_completion PathPrefix:drivers/scsi/scsi_error.c]
Results: map[Output:drivers/scsi/scsi_error.c=1196=static enum scsi_disposition scsi_send_eh_cmnd(struct scsi_cmnd *scmd,
--
drivers/scsi/scsi_error.c-1248- } else {
drivers/scsi/scsi_error.c:1249: timeleft = wait_for_completion_timeout(&done, timeout);
drivers/scsi/scsi_error.c-1250- rtn = SUCCESS;
]
|
| 36/2 |
2026/06/01 15:06 |
llm |
expert |
0m
Model:
Tokens:
input: 51748
output: 32
thoughts: 873
Thoughts: **Analyzing a Potential Kernel Hang**
Okay, so I'm looking at this kernel hang, and the `wait_for_completion_timeout` function has a task in the `TASK_UNINTERRUPTIBLE` state, which is a big red flag. The `scsi_eh` process could be waiting for a reset to finish, which would put it in that state, but it's not showing up as a hung task. Hmm...
Maybe the timeout is just set really long? Or perhaps the device isn't the expected USB mass storage? Could `sda1` be a loop device? No, those are named `loop0`. Wait, what about a virtio-blk device? Could syzkaller even emulate one? Syzkaller runs within a VM, so it's not directly controlling PCI devices unless it's using something like VFIO or vhost. But, syzkaller does have `vhost_vdpa` and `vhost_scsi` fuzzing capabilities, right?
If syzkaller uses `vhost_scsi`, it could definitely be creating a SCSI device called `sda`. If the syzkaller process acting as the `vhost_scsi` server hangs, the SCSI device itself will hang. Let's see if syzkaller is set up for `vhost_scsi`... yep, it does fuzz `/dev/vhost-scsi`. The kernel should create a SCSI device like `sda` (or `sdb`) when syzkaller opens and configures `/dev/vhost-scsi`. Then syzkaller mounts it and does I/O. The I/O goes to the `vhost_scsi` driver, which either sends it to a user-space process or handles it in kernel. Actually, the `vhost-scsi` driver is using a user-space virtqueue. If the user-space process doesn't process the virtqueue, the I/O will hang.
Does `vhost-scsi` even have a timeout? SCSI commands should have timeouts, and the SCSI error handler should try to abort the command. If that abort command is also sent to the virtqueue and not processed, then `scsi_eh` could hang. But again, `scsi_eh` is not in the hung task list.
Could this hang just be due to an enormous amount of I/O, with the disk just being painfully slow? Syzkaller generates a ton of I/O, and `wait_on_buffer` could definitely take a long time if the disk is struggling. 143 seconds is a long time, but it's *possible* on a heavily loaded QEMU VM with a slow host disk. But, syzkaller usually uses a memory-backed disk or a fast SSD for VMs, so that seems unlikely.
Wait, let's look at the tasks! `syz.0.346:7070` is in `do_page_mkwrite`. `syz.2.343:7067`, `syz.1.344:7068`, and `syz.3.345:7069` are all in `mmap`. All 4 syzkaller threads are blocked. `jbd2/sda1-8:5110` is also blocked, as is `kworker/u32:2:46`. This *really* looks like a complete I/O stall on `sda1`.
Now, the important question: Can an unprivileged user trigger this somehow? If it relies on `/dev/raw-gadget`, `/dev/vhost-scsi`, or `/dev/nbd0`, those all require root access. Can an unprivileged user mount a filesystem? Only via user namespaces, and only if the filesystem type is allowed. Ext4 isn't allowed, right? Let me double-check if ext4 has `FS_USERNS_MOUNT`... No, it doesn't.
|
| 37/2 |
2026/06/01 15:07 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/ext4/]
Results:
|
| 38/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 53528
output: 37
thoughts: 260
Thoughts: **Analyzing ext4 Mounting and Potential Deadlocks**
Okay, so ext4 filesystems can't be mounted by unprivileged users within a user namespace. That much is clear. This means that the mounting of `sda1` as an ext4 filesystem *had* to be done by root, probably through something like Syzkaller since it runs with root privileges (or at least has those capabilities in the initial namespace) to do things like mount filesystems.
This immediately tells me that if the bug *requires* mounting ext4 to trigger, then it's shielded. We're talking something that's inaccessible to unprivileged processes, and certainly inaccessible from within user namespaces.
But wait a minute... what if the ext4 filesystem was already mounted by the system administrator? Like, what if `sda1` *is* the root filesystem? If an unprivileged user can cause a hang on the *root* filesystem... that's a denial-of-service vulnerability, plain and simple.
The real question becomes: How could an unprivileged user potentially cause the root filesystem to hang? The answer probably lies in a bug in ext4 itself, or potentially in the journal (jbd2) that causes some sort of deadlock within those components.
Let's check the stack traces. Are there any deadlock indicators? Time to analyze the locks again. Specifically, I see `jbd2/sda1-8` is in `jbd2_journal_commit_transaction`. Based on my understanding of this function, it *shouldn't* be holding any locks. It drops the `j_state_lock` before waiting for buffers.
Let me double-check `jbd2_journal_commit_transaction` around line 837, and make sure that this is still true. It's a critical point to verify to see if the traces are correct.
|
| 39/2 |
2026/06/01 15:07 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/commit.c FirstLine:820 LineCount:30]
Results: map[Contents: 820: the log. Before we can commit it, wait for the IO so far to
821: complete. Control buffers being written are on the
822: transaction's t_log_list queue, and metadata buffers are on
823: the io_bufs list.
824:
825: Wait for the buffers in reverse order. That way we are
826: less likely to be woken up until all IOs have completed, and
827: so we incur less scheduling load.
828: */
829:
830: jbd2_debug(3, "JBD2: commit phase 3\n");
831:
832: while (!list_empty(&io_bufs)) {
833: struct buffer_head *bh = list_entry(io_bufs.prev,
834: struct buffer_head,
835: b_assoc_buffers);
836:
837: wait_on_buffer(bh);
838: cond_resched();
839:
840: if (unlikely(!buffer_uptodate(bh)))
841: err = -EIO;
842: jbd2_unfile_log_bh(bh);
843: stats.run.rs_blocks_logged++;
844:
845: /*
846: * The list contains temporary buffer heads created by
847: * jbd2_journal_write_metadata_buffer().
848: */
849: BUFFER_TRACE(bh, "dumping temporary bh");
]
|
| 40/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 54682
output: 31
thoughts: 270
Thoughts: **My Analysis of the Buffer Shadowing Mechanism**
Okay, so I'm looking at this code snippet, and my immediate observation is that it's designed to avoid holding any locks itself. It just passively waits for a buffer. The other tasks, the ones that *do* hold the locks, are actually waiting on the `BH_Shadow` bit within that buffer. That makes sense; it's a classic wait-on-bit scenario, ensuring that the necessary data is ready before proceeding.
Now, the crucial question pops up: who actually clears that `BH_Shadow` bit? I have to understand the lifecycle here. Let's see...Ah, right! The `jbd2_journal_commit_transaction` function handles the clearing. It does so *after* calling `wait_on_buffer(bh)`. That seems correct. I can see the code now: it retrieves the buffer from `t_shadow_list`, clears `buffer_jwrite`, and then importantly, asserts that it's still dirty but *not* shadowed. This is the expected behavior, confirming the shadow has been handled.
Wait a second... Is `clear_buffer_shadow(bh)` called *only* within `jbd2_journal_commit_transaction`? It's possible the bit is cleared somewhere else, too. We need to be absolutely sure we understand every possible scenario here. I'm going to search for other instances of the `clear_buffer_shadow` function to see if there is any other place where it is set. That's the best way to get a complete picture of the shadowing and unshadowing logic.
|
| 41/2 |
2026/06/01 15:07 |
tool |
grepper |
0m
Error:
Args: map[Expression:clear_buffer_shadow PathPrefix:fs/jbd2/]
Results:
|
| 42/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 55342
output: 29
thoughts: 10
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Investigating the "BH_Shadow" Phenomenon**
Alright, let's get down to business. My initial thought process revolves around pinpointing exactly what's being referred to with this search term, "BH_Shadow". Now, I'm already mentally sifting through possible contexts. Is this related to simulations, astrophysical observations, theoretical models, or perhaps even a code name within a project I haven't come across yet? My background in this subject gives me an arsenal of fields to search. The underscore is a good clue - itβs probably a variable name in some code or research output, or maybe a file name structure. Iβm thinking about how I'd approach tracking this down. Do I start with my own local databases, or is this the kind of inquiry that needs a broader literature search, perhaps using a specialized academic search engine or maybe even a specific archive? Let's get moving!
|
| 43/2 |
2026/06/01 15:07 |
tool |
grepper |
0m
Args: map[Expression:BH_Shadow PathPrefix:fs/jbd2/]
Results: map[Output:fs/jbd2/commit.c=32=static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
--
fs/jbd2/commit.c-41- if (orig_bh) {
fs/jbd2/commit.c:42: clear_bit_unlock(BH_Shadow, &orig_bh->b_state);
fs/jbd2/commit.c-43- smp_mb__after_atomic();
fs/jbd2/commit.c:44: wake_up_bit(&orig_bh->b_state, BH_Shadow);
fs/jbd2/commit.c-45- }
--
fs/jbd2/transaction.c=948=do_get_write_access(handle_t *handle, struct journal_head *jh,
--
fs/jbd2/transaction.c-1112- spin_unlock(&jh->b_state_lock);
fs/jbd2/transaction.c:1113: wait_on_bit_io(&bh->b_state, BH_Shadow, TASK_UNINTERRUPTIBLE);
fs/jbd2/transaction.c-1114- goto repeat;
--
fs/jbd2/transaction.c-1119- * If buffer isn't on BJ_Metadata list, the committing transaction is
fs/jbd2/transaction.c:1120: * past that stage (here we use the fact that BH_Shadow is set under
fs/jbd2/transaction.c-1121- * bh_state lock together with refiling to BJ_Shadow list and at this
fs/jbd2/transaction.c:1122: * point we know the buffer doesn't have BH_Shadow set).
fs/jbd2/transaction.c-1123- *
]
|
| 44/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 56063
output: 32
thoughts: 1041
Thoughts: **Analyzing a Block IO Hang**
Okay, so `journal_end_buffer_io_sync` is the key here. It clears `BH_Shadow` and wakes up waiters when the block IO completes. Basically, it's the completion handler. When block IO finishes, this function does the cleanup. It clears `BH_Shadow` on the original buffer and wakes up `do_get_write_access` and also unlocks the temporary buffer, waking up `wait_on_buffer(bh)` within `jbd2_journal_commit_transaction`.
So both `do_get_write_access` and `jbd2_journal_commit_transaction` are waiting for this completion. That's a critical dependency. If the block IO *never* completes, both threads will hang indefinitely. This screams "block IO hang" to me.
The likely culprit? Syzkaller and its love for creating loopback block devices. Think NBD or maybe even something like USB mass storage emulated in user-space. We've seen this before: the user-space IO handler goes AWOL, the block device becomes unresponsive, and the filesystem mounted on it is toast. It's a classic case.
But is there a security impact? If an unprivileged user could create such a device and mount a filesystem, they *could* hang their filesystem. However, this wouldn't be a system-wide DoS, unless they manage to exhaust all resources, or acquire locks that affect others. Wait, since the threads are holding `mmap_lock` and `sb_writers`, maybe they *could* block others. But still, it's their own filesystem. And can an unprivileged user even do this? No, that requires root. Creating NBD or USB mass storage, mounting ext4, all require root privileges.
But what if, for instance, the root filesystem is `sda1`, and the IO hangs due to a bug in QEMU's block layer or the host machine? If it's a QEMU or host bug, it's not a guest kernel bug. What about a bug in the guest's virtio-blk driver? Well, there are no virtio functions in the stack trace. The IO is submitted and then disappears into the ether. A virtio-blk bug *would* be a guest kernel bug, of course.
The smoking gun here is syzkaller's tendency to create these user-space block devices. Given the `nbd1-recv` workers, itβs almost certain this is an NBD device. Now, if syzkaller creates an NBD device and mounts ext4 on it, the relevant jbd2 thread would typically be named something like `jbd2/nbd1-8`. The name, however, is `jbd2/sda1-8`.
Aha! Maybe syzkaller is using `vhost-scsi`? That would create a SCSI device, likely `sda`, and then a partition like `sda1`. Bingo! The jbd2 thread would be `jbd2/sda1-8`. The `vhost-scsi` server would be a syzkaller process. If the syzkaller process hangs, `sda1` hangs. This perfectly explains the observed thread name and the hang.
Let's confirm. Does syzkaller fuzz `vhost-scsi`? Yes! Syzkaller has `syz_open_dev$vhost_scsi`. Opening `/dev/vhost-scsi` also requires root. So unprivileged users are blocked. Is it accessible in a user namespace? Device nodes are not, by default. And even if it *was*, `vhost-scsi` likely requires global capabilities or just root. Time to check `vhost-scsi` permissions.
|
| 45/2 |
2026/06/01 15:07 |
tool |
grepper |
0m
Args: map[Expression:vhost_scsi_open PathPrefix:drivers/vhost/]
Results: map[Output:drivers/vhost/scsi.c=2218=static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features)
--
drivers/vhost/scsi.c-2270-
drivers/vhost/scsi.c:2271:static int vhost_scsi_open(struct inode *inode, struct file *f)
drivers/vhost/scsi.c-2272-{
--
drivers/vhost/scsi.c=2437=static const struct file_operations vhost_scsi_fops = {
--
drivers/vhost/scsi.c-2441- .compat_ioctl = compat_ptr_ioctl,
drivers/vhost/scsi.c:2442: .open = vhost_scsi_open,
drivers/vhost/scsi.c-2443- .llseek = noop_llseek,
]
|
| 46/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 58196
output: 38
thoughts: 13
Thoughts: Okay, let's dive into this. Here's my thought process on this:
**Analyzing `vhost_scsi_open`**
Alright, time to focus. I'm starting with `vhost_scsi_open`. I'm already visualizing the SCSI driver interaction, the vhost layer, and how it all comes together in this function. My mind's racing through the possible entry points, the data structures it might be manipulating, and the potential areas for optimization or, heaven forbid, bugs. I need to understand this function's role in the larger picture of vhost-scsi. Is it just about opening the connection? Allocating resources? Initializing things? What are the implications of this particular function failing? Let's trace through it.
|
| 47/2 |
2026/06/01 15:07 |
tool |
read-file |
0m
Args: map[File:drivers/vhost/scsi.c FirstLine:2260 LineCount:30]
Results: map[Contents:2260: mutex_lock(&vq->mutex);
2261: vhost_scsi_destroy_vq_log(vq);
2262: mutex_unlock(&vq->mutex);
2263: }
2264: }
2265:
2266: out:
2267: mutex_unlock(&vs->dev.mutex);
2268: return 0;
2269: }
2270:
2271: static int vhost_scsi_open(struct inode *inode, struct file *f)
2272: {
2273: struct vhost_scsi_virtqueue *svq;
2274: struct vhost_scsi *vs;
2275: struct vhost_virtqueue **vqs;
2276: int r = -ENOMEM, i, nvqs = vhost_scsi_max_io_vqs;
2277:
2278: vs = kvzalloc_obj(*vs);
2279: if (!vs)
2280: goto err_vs;
2281: vs->inline_sg_cnt = vhost_scsi_inline_sg_cnt;
2282:
2283: if (nvqs > VHOST_SCSI_MAX_IO_VQ) {
2284: pr_err("Invalid max_io_vqs of %d. Using %d.\n", nvqs,
2285: VHOST_SCSI_MAX_IO_VQ);
2286: nvqs = VHOST_SCSI_MAX_IO_VQ;
2287: } else if (nvqs == 0) {
2288: pr_err("Invalid max_io_vqs of %d. Using 1.\n", nvqs);
2289: nvqs = 1;
]
|
| 48/2 |
2026/06/01 15:07 |
llm |
expert |
0m
Model:
Tokens:
input: 58911
output: 36
thoughts: 531
Thoughts: **Analyzing Potential Peripheral-Triggered DoS Scenarios**
Okay, so I'm thinking about this `vhost_scsi_open` function and whether there's a security hole. I noticed there's no capability check there, but that `/dev/vhost-scsi` is created by `misc_register` with mode 0600, root-owned. So, unprivileged users can't open it. That's good, but it prompted me to look at similar cases like USB mass storage, NBD, and loop devices. All of them - `/dev/raw-gadget`, `/dev/nbd0`, `/dev/loop-control` - are also root-owned and mode 0600. So, it's consistent: You need root to create these block devices.
The implication? If root creates a user-space backed block device and that user-space process hangs, the block device hangs. It's expected behaviour; the kernel can't magically prevent a user-space process from freezing. It'll just wait on the IO, which leads to a hung task warning, which syzkaller flags as a bug. But from a security perspective, it's not a *security* bug; it's a DoS, but one that requires root.
Now, I'm trying to stretch my imagination and think about a *peripheral* trigger. Could a malicious filesystem image on a removable device like a USB stick cause a hang? If an attacker plugs in a bad USB mass storage device, and it auto-mounts...then what if that device simply *stops* responding to SCSI commands? The kernel's SCSI layer would wait, then the SCSI error handler gets invoked to try a reset. If the USB device ignores the reset commands, the error handler *could* hang, or eventually offline the device. But if it hangs, say goodbye to the `jbd2` thread - forever hung. A DoS (hung tasks, unkillable processes)!
Is this a valid peripheral DoS? It *feels* right, and yes, it seems so, if a USB device can hang the kernel simply by not responding. But wait...the SCSI error handler is *designed* to handle unresponsive devices! It should eventually offline the device. The critical question: Can the SCSI error handler itself hang forever? I need to dig deeper and see if the design is solid enough to prevent this or not.
|
| 49/2 |
2026/06/01 15:08 |
tool |
grepper |
0m
Args: map[Expression:scsi_eh_ PathPrefix:drivers/scsi/scsi_error.c]
Results: map[Output:drivers/scsi/scsi_error.c-59-
drivers/scsi/scsi_error.c:60:static int scsi_eh_try_stu(struct scsi_cmnd *scmd);
drivers/scsi/scsi_error.c-61-static enum scsi_disposition scsi_try_to_abort_cmd(const struct scsi_host_template *,
--
drivers/scsi/scsi_error.c-63-
drivers/scsi/scsi_error.c:64:void scsi_eh_wakeup(struct Scsi_Host *shost, unsigned int busy)
drivers/scsi/scsi_error.c-65-{
--
drivers/scsi/scsi_error.c-68- if (busy == shost->host_failed) {
drivers/scsi/scsi_error.c:69: trace_scsi_eh_wakeup(shost);
drivers/scsi/scsi_error.c-70- wake_up_process(shost->ehandler);
--
drivers/scsi/scsi_error.c=82=void scsi_schedule_eh(struct Scsi_Host *shost)
--
drivers/scsi/scsi_error.c-90- shost->host_eh_scheduled++;
drivers/scsi/scsi_error.c:91: scsi_eh_wakeup(shost, scsi_host_busy(shost));
drivers/scsi/scsi_error.c-92- }
--
drivers/scsi/scsi_error.c=117=static bool scsi_cmd_retry_allowed(struct scsi_cmnd *cmd)
--
drivers/scsi/scsi_error.c-124-
drivers/scsi/scsi_error.c:125:static bool scsi_eh_should_retry_cmd(struct scsi_cmnd *cmd)
drivers/scsi/scsi_error.c-126-{
--
drivers/scsi/scsi_error.c=147=scmd_eh_abort_handler(struct work_struct *work)
--
drivers/scsi/scsi_error.c-199- scsi_cmd_retry_allowed(scmd) &&
drivers/scsi/scsi_error.c:200: scsi_eh_should_retry_cmd(scmd)) {
drivers/scsi/scsi_error.c-201- SCSI_LOG_ERROR_RECOVERY(3,
--
drivers/scsi/scsi_error.c-217-
drivers/scsi/scsi_error.c:218: scsi_eh_scmd_add(scmd);
drivers/scsi/scsi_error.c-219-}
--
drivers/scsi/scsi_error.c=228=scsi_abort_command(struct scsi_cmnd *scmd)
--
drivers/scsi/scsi_error.c-264-/**
drivers/scsi/scsi_error.c:265: * scsi_eh_reset - call into ->eh_action to reset internal counters
drivers/scsi/scsi_error.c-266- * @scmd: scmd to run eh on.
--
drivers/scsi/scsi_error.c-271- */
drivers/scsi/scsi_error.c:272:static void scsi_eh_reset(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-273-{
--
drivers/scsi/scsi_error.c-280-
drivers/scsi/scsi_error.c:281:static void scsi_eh_inc_host_failed(struct rcu_head *head)
drivers/scsi/scsi_error.c-282-{
--
drivers/scsi/scsi_error.c-298- spin_lock_irqsave(shost->host_lock, flags);
drivers/scsi/scsi_error.c:299: scsi_eh_wakeup(shost, busy);
drivers/scsi/scsi_error.c-300- spin_unlock_irqrestore(shost->host_lock, flags);
--
drivers/scsi/scsi_error.c-303-/**
drivers/scsi/scsi_error.c:304: * scsi_eh_scmd_add - add scsi cmd to error handling.
drivers/scsi/scsi_error.c-305- * @scmd: scmd to run eh on.
drivers/scsi/scsi_error.c-306- */
drivers/scsi/scsi_error.c:307:void scsi_eh_scmd_add(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-308-{
--
drivers/scsi/scsi_error.c-323-
drivers/scsi/scsi_error.c:324: scsi_eh_reset(scmd);
drivers/scsi/scsi_error.c-325- list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
--
drivers/scsi/scsi_error.c-330- */
drivers/scsi/scsi_error.c:331: call_rcu_hurry(&scmd->rcu, scsi_eh_inc_host_failed);
drivers/scsi/scsi_error.c-332-}
--
drivers/scsi/scsi_error.c=344=enum blk_eh_timer_return scsi_timeout(struct request *req)
--
drivers/scsi/scsi_error.c-375- set_host_byte(scmd, DID_TIME_OUT);
drivers/scsi/scsi_error.c:376: scsi_eh_scmd_add(scmd);
drivers/scsi/scsi_error.c-377- }
--
drivers/scsi/scsi_error.c=403=EXPORT_SYMBOL(scsi_block_when_processing_errors);
--
drivers/scsi/scsi_error.c-406-/**
drivers/scsi/scsi_error.c:407: * scsi_eh_prt_fail_stats - Log info on failures.
drivers/scsi/scsi_error.c-408- * @shost: scsi host being recovered.
--
drivers/scsi/scsi_error.c-410- */
drivers/scsi/scsi_error.c:411:static inline void scsi_eh_prt_fail_stats(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-412- struct list_head *work_q)
--
drivers/scsi/scsi_error.c=791=static void scsi_handle_queue_full(struct scsi_device *sdev)
--
drivers/scsi/scsi_error.c-812-/**
drivers/scsi/scsi_error.c:813: * scsi_eh_completed_normally - Disposition a eh cmd on return from LLD.
drivers/scsi/scsi_error.c-814- * @scmd: SCSI cmd to examine.
--
drivers/scsi/scsi_error.c-821- */
drivers/scsi/scsi_error.c:822:static enum scsi_disposition scsi_eh_completed_normally(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-823-{
--
drivers/scsi/scsi_error.c-885-/**
drivers/scsi/scsi_error.c:886: * scsi_eh_done - Completion function for error handling.
drivers/scsi/scsi_error.c-887- * @scmd: Cmd that is done.
drivers/scsi/scsi_error.c-888- */
drivers/scsi/scsi_error.c:889:void scsi_eh_done(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-890-{
--
drivers/scsi/scsi_error.c=1048=static void scsi_abort_eh_cmnd(struct scsi_cmnd *scmd)
--
drivers/scsi/scsi_error.c-1057-/**
drivers/scsi/scsi_error.c:1058: * scsi_eh_prep_cmnd - Save a scsi command info as part of error recovery
drivers/scsi/scsi_error.c-1059- * @scmd: SCSI command structure to hijack
--
drivers/scsi/scsi_error.c-1070- */
drivers/scsi/scsi_error.c:1071:void scsi_eh_prep_cmnd(struct scsi_cmnd *scmd, struct scsi_eh_save *ses,
drivers/scsi/scsi_error.c-1072- unsigned char *cmnd, int cmnd_size, unsigned sense_bytes)
--
drivers/scsi/scsi_error.c-1146-}
drivers/scsi/scsi_error.c:1147:EXPORT_SYMBOL(scsi_eh_prep_cmnd);
drivers/scsi/scsi_error.c-1148-
drivers/scsi/scsi_error.c-1149-/**
drivers/scsi/scsi_error.c:1150: * scsi_eh_restore_cmnd - Restore a scsi command info as part of error recovery
drivers/scsi/scsi_error.c-1151- * @scmd: SCSI command structure to restore
drivers/scsi/scsi_error.c:1152: * @ses: saved information from a coresponding call to scsi_eh_prep_cmnd
drivers/scsi/scsi_error.c-1153- *
drivers/scsi/scsi_error.c:1154: * Undo any damage done by above scsi_eh_prep_cmnd().
drivers/scsi/scsi_error.c-1155- */
drivers/scsi/scsi_error.c:1156:void scsi_eh_restore_cmnd(struct scsi_cmnd* scmd, struct scsi_eh_save *ses)
drivers/scsi/scsi_error.c-1157-{
--
drivers/scsi/scsi_error.c-1179-}
drivers/scsi/scsi_error.c:1180:EXPORT_SYMBOL(scsi_eh_restore_cmnd);
drivers/scsi/scsi_error.c-1181-
--
drivers/scsi/scsi_error.c-1190- * This function is used to send a scsi command down to a target device
drivers/scsi/scsi_error.c:1191: * as part of the error recovery process. See also scsi_eh_prep_cmnd() above.
drivers/scsi/scsi_error.c-1192- *
--
drivers/scsi/scsi_error.c=1196=static enum scsi_disposition scsi_send_eh_cmnd(struct scsi_cmnd *scmd,
--
drivers/scsi/scsi_error.c-1202- unsigned long timeleft = timeout, delay;
drivers/scsi/scsi_error.c:1203: struct scsi_eh_save ses;
drivers/scsi/scsi_error.c-1204- const unsigned long stall_for = msecs_to_jiffies(100);
--
drivers/scsi/scsi_error.c-1207-retry:
drivers/scsi/scsi_error.c:1208: scsi_eh_prep_cmnd(scmd, &ses, cmnd, cmnd_size, sense_bytes);
drivers/scsi/scsi_error.c-1209- shost->eh_action = &done;
--
drivers/scsi/scsi_error.c-1238- if (timeleft > stall_for) {
drivers/scsi/scsi_error.c:1239: scsi_eh_restore_cmnd(scmd, &ses);
drivers/scsi/scsi_error.c-1240-
--
drivers/scsi/scsi_error.c-1261- /*
drivers/scsi/scsi_error.c:1262: * If there is time left scsi_eh_done got called, and we will examine
drivers/scsi/scsi_error.c-1263- * the actual status codes to see whether the command actually did
--
drivers/scsi/scsi_error.c-1270- if (timeleft) {
drivers/scsi/scsi_error.c:1271: rtn = scsi_eh_completed_normally(scmd);
drivers/scsi/scsi_error.c-1272- SCSI_LOG_ERROR_RECOVERY(3, scmd_printk(KERN_INFO, scmd,
drivers/scsi/scsi_error.c:1273: "%s: scsi_eh_completed_normally %x\n", __func__, rtn));
drivers/scsi/scsi_error.c-1274-
--
drivers/scsi/scsi_error.c-1291-
drivers/scsi/scsi_error.c:1292: scsi_eh_restore_cmnd(scmd, &ses);
drivers/scsi/scsi_error.c-1293-
--
drivers/scsi/scsi_error.c=1311=static enum scsi_disposition
drivers/scsi/scsi_error.c:1312:scsi_eh_action(struct scsi_cmnd *scmd, enum scsi_disposition rtn)
drivers/scsi/scsi_error.c-1313-{
--
drivers/scsi/scsi_error.c-1322-/**
drivers/scsi/scsi_error.c:1323: * scsi_eh_finish_cmd - Handle a cmd that eh is finished with.
drivers/scsi/scsi_error.c-1324- * @scmd: Original SCSI cmd that eh has finished.
--
drivers/scsi/scsi_error.c-1333- */
drivers/scsi/scsi_error.c:1334:void scsi_eh_finish_cmd(struct scsi_cmnd *scmd, struct list_head *done_q)
drivers/scsi/scsi_error.c-1335-{
--
drivers/scsi/scsi_error.c-1337-}
drivers/scsi/scsi_error.c:1338:EXPORT_SYMBOL(scsi_eh_finish_cmd);
drivers/scsi/scsi_error.c-1339-
drivers/scsi/scsi_error.c-1340-/**
drivers/scsi/scsi_error.c:1341: * scsi_eh_get_sense - Get device sense data.
drivers/scsi/scsi_error.c-1342- * @work_q: Queue of commands to process.
--
drivers/scsi/scsi_error.c-1359- */
drivers/scsi/scsi_error.c:1360:int scsi_eh_get_sense(struct list_head *work_q,
drivers/scsi/scsi_error.c-1361- struct list_head *done_q)
--
drivers/scsi/scsi_error.c-1425-
drivers/scsi/scsi_error.c:1426: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1427- }
--
drivers/scsi/scsi_error.c-1430-}
drivers/scsi/scsi_error.c:1431:EXPORT_SYMBOL_GPL(scsi_eh_get_sense);
drivers/scsi/scsi_error.c-1432-
drivers/scsi/scsi_error.c-1433-/**
drivers/scsi/scsi_error.c:1434: * scsi_eh_tur - Send TUR to device.
drivers/scsi/scsi_error.c-1435- * @scmd: &scsi_cmnd to send TUR
--
drivers/scsi/scsi_error.c-1439- */
drivers/scsi/scsi_error.c:1440:static int scsi_eh_tur(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-1441-{
--
drivers/scsi/scsi_error.c-1465-/**
drivers/scsi/scsi_error.c:1466: * scsi_eh_test_devices - check if devices are responding from error recovery.
drivers/scsi/scsi_error.c-1467- * @cmd_list: scsi commands in error recovery.
--
drivers/scsi/scsi_error.c-1477- **/
drivers/scsi/scsi_error.c:1478:static int scsi_eh_test_devices(struct list_head *cmd_list,
drivers/scsi/scsi_error.c-1479- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1502- finish_cmds = !scsi_device_online(scmd->device) ||
drivers/scsi/scsi_error.c:1503: (try_stu && !scsi_eh_try_stu(scmd) &&
drivers/scsi/scsi_error.c:1504: !scsi_eh_tur(scmd)) ||
drivers/scsi/scsi_error.c:1505: !scsi_eh_tur(scmd);
drivers/scsi/scsi_error.c-1506-
--
drivers/scsi/scsi_error.c-1510- (try_stu ||
drivers/scsi/scsi_error.c:1511: scsi_eh_action(scmd, SUCCESS) == SUCCESS))
drivers/scsi/scsi_error.c:1512: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1513- else
--
drivers/scsi/scsi_error.c-1520-/**
drivers/scsi/scsi_error.c:1521: * scsi_eh_try_stu - Send START_UNIT to device.
drivers/scsi/scsi_error.c-1522- * @scmd: &scsi_cmnd to send START_UNIT
--
drivers/scsi/scsi_error.c-1526- */
drivers/scsi/scsi_error.c:1527:static int scsi_eh_try_stu(struct scsi_cmnd *scmd)
drivers/scsi/scsi_error.c-1528-{
--
drivers/scsi/scsi_error.c-1546- /**
drivers/scsi/scsi_error.c:1547: * scsi_eh_stu - send START_UNIT if needed
drivers/scsi/scsi_error.c-1548- * @shost: &scsi host being recovered.
--
drivers/scsi/scsi_error.c-1555- */
drivers/scsi/scsi_error.c:1556:static int scsi_eh_stu(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-1557- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1587-
drivers/scsi/scsi_error.c:1588: if (!scsi_eh_try_stu(stu_scmd)) {
drivers/scsi/scsi_error.c-1589- if (!scsi_device_online(sdev) ||
drivers/scsi/scsi_error.c:1590: !scsi_eh_tur(stu_scmd)) {
drivers/scsi/scsi_error.c-1591- list_for_each_entry_safe(scmd, next,
--
drivers/scsi/scsi_error.c-1593- if (scmd->device == sdev &&
drivers/scsi/scsi_error.c:1594: scsi_eh_action(scmd, SUCCESS) == SUCCESS)
drivers/scsi/scsi_error.c:1595: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1596- }
--
drivers/scsi/scsi_error.c-1610-/**
drivers/scsi/scsi_error.c:1611: * scsi_eh_bus_device_reset - send bdr if needed
drivers/scsi/scsi_error.c-1612- * @shost: scsi host being recovered.
--
drivers/scsi/scsi_error.c-1621- */
drivers/scsi/scsi_error.c:1622:static int scsi_eh_bus_device_reset(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-1623- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1655- rtn == FAST_IO_FAIL ||
drivers/scsi/scsi_error.c:1656: !scsi_eh_tur(bdr_scmd)) {
drivers/scsi/scsi_error.c-1657- list_for_each_entry_safe(scmd, next,
--
drivers/scsi/scsi_error.c-1659- if (scmd->device == sdev &&
drivers/scsi/scsi_error.c:1660: scsi_eh_action(scmd, rtn) != FAILED)
drivers/scsi/scsi_error.c:1661: scsi_eh_finish_cmd(scmd,
drivers/scsi/scsi_error.c-1662- done_q);
--
drivers/scsi/scsi_error.c-1675-/**
drivers/scsi/scsi_error.c:1676: * scsi_eh_target_reset - send target reset if needed
drivers/scsi/scsi_error.c-1677- * @shost: scsi host being recovered.
--
drivers/scsi/scsi_error.c-1683- */
drivers/scsi/scsi_error.c:1684:static int scsi_eh_target_reset(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-1685- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1729- else if (rtn == FAST_IO_FAIL)
drivers/scsi/scsi_error.c:1730: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1731- else
--
drivers/scsi/scsi_error.c-1736-
drivers/scsi/scsi_error.c:1737: return scsi_eh_test_devices(&check_list, work_q, done_q, 0);
drivers/scsi/scsi_error.c-1738-}
--
drivers/scsi/scsi_error.c-1740-/**
drivers/scsi/scsi_error.c:1741: * scsi_eh_bus_reset - send a bus reset
drivers/scsi/scsi_error.c-1742- * @shost: &scsi host being recovered.
--
drivers/scsi/scsi_error.c-1745- */
drivers/scsi/scsi_error.c:1746:static int scsi_eh_bus_reset(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-1747- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1794- if (rtn == FAST_IO_FAIL)
drivers/scsi/scsi_error.c:1795: scsi_eh_finish_cmd(scmd,
drivers/scsi/scsi_error.c-1796- done_q);
--
drivers/scsi/scsi_error.c-1808- }
drivers/scsi/scsi_error.c:1809: return scsi_eh_test_devices(&check_list, work_q, done_q, 0);
drivers/scsi/scsi_error.c-1810-}
--
drivers/scsi/scsi_error.c-1812-/**
drivers/scsi/scsi_error.c:1813: * scsi_eh_host_reset - send a host reset
drivers/scsi/scsi_error.c-1814- * @shost: host to be reset.
--
drivers/scsi/scsi_error.c-1817- */
drivers/scsi/scsi_error.c:1818:static int scsi_eh_host_reset(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-1819- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-1839- list_for_each_entry_safe(scmd, next, work_q, eh_entry) {
drivers/scsi/scsi_error.c:1840: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1841- }
--
drivers/scsi/scsi_error.c-1848- }
drivers/scsi/scsi_error.c:1849: return scsi_eh_test_devices(&check_list, work_q, done_q, 1);
drivers/scsi/scsi_error.c-1850-}
--
drivers/scsi/scsi_error.c-1852-/**
drivers/scsi/scsi_error.c:1853: * scsi_eh_offline_sdevs - offline scsi devices that fail to recover
drivers/scsi/scsi_error.c-1854- * @work_q: &list_head for pending commands.
--
drivers/scsi/scsi_error.c-1856- */
drivers/scsi/scsi_error.c:1857:static void scsi_eh_offline_sdevs(struct list_head *work_q,
drivers/scsi/scsi_error.c-1858- struct list_head *done_q)
--
drivers/scsi/scsi_error.c-1871-
drivers/scsi/scsi_error.c:1872: scsi_eh_finish_cmd(scmd, done_q);
drivers/scsi/scsi_error.c-1873- }
--
drivers/scsi/scsi_error.c=2120=static enum rq_end_io_ret eh_lock_door_done(struct request *req,
--
drivers/scsi/scsi_error.c-2128-/**
drivers/scsi/scsi_error.c:2129: * scsi_eh_lock_door - Prevent medium removal for the specified device
drivers/scsi/scsi_error.c-2130- * @sdev: SCSI device to prevent medium removal
--
drivers/scsi/scsi_error.c-2138- */
drivers/scsi/scsi_error.c:2139:static void scsi_eh_lock_door(struct scsi_device *sdev)
drivers/scsi/scsi_error.c-2140-{
--
drivers/scsi/scsi_error.c=2173=static void scsi_restart_operations(struct Scsi_Host *shost)
--
drivers/scsi/scsi_error.c-2184- if (scsi_device_online(sdev) && sdev->was_reset && sdev->locked) {
drivers/scsi/scsi_error.c:2185: scsi_eh_lock_door(sdev);
drivers/scsi/scsi_error.c-2186- sdev->was_reset = 0;
--
drivers/scsi/scsi_error.c-2229-/**
drivers/scsi/scsi_error.c:2230: * scsi_eh_ready_devs - check device ready state and recover if not.
drivers/scsi/scsi_error.c-2231- * @shost: host to be recovered.
--
drivers/scsi/scsi_error.c-2234- */
drivers/scsi/scsi_error.c:2235:void scsi_eh_ready_devs(struct Scsi_Host *shost,
drivers/scsi/scsi_error.c-2236- struct list_head *work_q,
--
drivers/scsi/scsi_error.c-2238-{
drivers/scsi/scsi_error.c:2239: if (!scsi_eh_stu(shost, work_q, done_q))
drivers/scsi/scsi_error.c:2240: if (!scsi_eh_bus_device_reset(shost, work_q, done_q))
drivers/scsi/scsi_error.c:2241: if (!scsi_eh_target_reset(shost, work_q, done_q))
drivers/scsi/scsi_error.c:2242: if (!scsi_eh_bus_reset(shost, work_q, done_q))
drivers/scsi/scsi_error.c:2243: if (!scsi_eh_host_reset(shost, work_q, done_q))
drivers/scsi/scsi_error.c:2244: scsi_eh_offline_sdevs(work_q,
drivers/scsi/scsi_error.c-2245- done_q);
drivers/scsi/scsi_error.c-2246-}
drivers/scsi/scsi_error.c:2247:EXPORT_SYMBOL_GPL(scsi_eh_ready_devs);
drivers/scsi/scsi_error.c-2248-
drivers/scsi/scsi_error.c-2249-/**
drivers/scsi/scsi_error.c:2250: * scsi_eh_flush_done_q - finish processed commands or retry them.
drivers/scsi/scsi_error.c-2251- * @done_q: list_head of processed commands.
drivers/scsi/scsi_error.c-2252- */
drivers/scsi/scsi_error.c:2253:void scsi_eh_flush_done_q(struct list_head *done_q)
drivers/scsi/scsi_error.c-2254-{
--
drivers/scsi/scsi_error.c-2262- scsi_cmd_retry_allowed(scmd) &&
drivers/scsi/scsi_error.c:2263: scsi_eh_should_retry_cmd(scmd)) {
drivers/scsi/scsi_error.c-2264- SCSI_LOG_ERROR_RECOVERY(3,
--
drivers/scsi/scsi_error.c-2272- * If just we got sense for the device (called
drivers/scsi/scsi_error.c:2273: * scsi_eh_get_sense), scmd->result is already
drivers/scsi/scsi_error.c-2274- * set, do not set DID_TIME_OUT.
--
drivers/scsi/scsi_error.c-2286-}
drivers/scsi/scsi_error.c:2287:EXPORT_SYMBOL(scsi_eh_flush_done_q);
drivers/scsi/scsi_error.c-2288-
--
drivers/scsi/scsi_error.c=2312=static void scsi_unjam_host(struct Scsi_Host *shost)
--
drivers/scsi/scsi_error.c-2321-
drivers/scsi/scsi_error.c:2322: SCSI_LOG_ERROR_RECOVERY(1, scsi_eh_prt_fail_stats(shost, &eh_work_q));
drivers/scsi/scsi_error.c-2323-
drivers/scsi/scsi_error.c:2324: if (!scsi_eh_get_sense(&eh_work_q, &eh_done_q))
drivers/scsi/scsi_error.c:2325: scsi_eh_ready_devs(shost, &eh_work_q, &eh_done_q);
drivers/scsi/scsi_error.c-2326-
--
drivers/scsi/scsi_error.c-2330- spin_unlock_irqrestore(shost->host_lock, flags);
drivers/scsi/scsi_error.c:2331: scsi_eh_flush_done_q(&eh_done_q);
drivers/scsi/scsi_error.c-2332-}
--
drivers/scsi/scsi_error.c=2342=int scsi_error_handler(void *data)
--
drivers/scsi/scsi_error.c-2366- shost_printk(KERN_INFO, shost,
drivers/scsi/scsi_error.c:2367: "scsi_eh_%d: sleeping\n",
drivers/scsi/scsi_error.c-2368- shost->host_no));
--
drivers/scsi/scsi_error.c-2375- shost_printk(KERN_INFO, shost,
drivers/scsi/scsi_error.c:2376: "scsi_eh_%d: waking up %d/%d/%d\n",
drivers/scsi/scsi_error.c-2377- shost->host_no, shost->host_eh_scheduled,
--
drivers/scsi/scsi_error.c-2388- shost_printk(KERN_ERR, shost,
drivers/scsi/scsi_error.c:2389: "scsi_eh_%d: unable to autoresume\n",
drivers/scsi/scsi_error.c-2390- shost->host_no));
--
drivers/scsi/scsi_error.c-2416- shost_printk(KERN_INFO, shost,
drivers/scsi/scsi_error.c:2417: "Error handler scsi_eh_%d exiting\n",
drivers/scsi/scsi_error.c-2418- shost->host_no));
]
|
| 50/2 |
2026/06/01 15:08 |
llm |
expert |
0m
Model:
Tokens:
input: 69103
output: 38
thoughts: 3350
Thoughts: **Analysis of Potential Block Device Hang and Root Cause**
Okay, let's break this down. We have a SCSI error handler thread (`scsi_eh`) that's getting stuck. It's not in the hung task list, which initially seems odd, because if it was blocked waiting for completion with a timeout, it _should_ be in the `D` state. However, the timeout mechanism in `wait_for_completion_timeout` uses `TASK_UNINTERRUPTIBLE`, implying a blocking state, but it also means the task *wakes up* after the timeout expires. This is key, as `khungtaskd` (the "kernel hung task detector") only flags tasks that have been in the `D` state *continuously* for a certain duration (143 seconds in this case).
The timeout behavior resets the task's context switch count (`nvcsw`), thus evading `khungtaskd`'s detection. Essentially, `scsi_eh` is caught in a loop: trying to reset the device (or bus), timing out, retrying. If a USB device, emulated by something like syzkaller, just flat-out ignores commands and resets, `scsi_eh` will spend considerable time in error recovery. That means the IO doesn't complete. That's why `wait_on_buffer` is hanging continuously for 143 seconds. Thatβs whatβs preventing the journal from committing. This also explains why the `scsi_eh` handler isnβt flagged by `khungtaskd`, but `jbd2` is. The root cause is a user-space emulated block device (like USB mass storage) that isnβt responding to IO and resets. This is known behavior, not a kernel bug, but a DoS.
Since creating such a device requires root privileges (or at least access to `/dev/raw-gadget`), itβs not accessible to unprivileged processes. Is this a Peripheral Trigger? Yes, a malicious USB mass storage device could cause this DoS. Is it Exploitable? No, it's just a DoS. Is it a Malicious Filesystem Trigger? No, the filesystem itself isn't malicious; the block device is just hanging, or a bug is in the device layer.
Could it be network-related? No. VM related? No. So, `NetworkTrigger`, `VMGuestTrigger` and `VMHostTrigger` are all false.
Now, let's explore other triggers. What about the Network Block Device (NBD)? If an NBD server hangs, then NBD IO hangs, right? Does NBD have a timeout? Yes, NBD has a timeout, so it aborts the IO and returns `-EIO`. However, syzkaller can set the NBD timeout to 0 (infinite). If the timeout is infinite, the IO hangs forever. This is bad. Can an unprivileged user create an NBD device? No, it requires root. Can it be triggered remotely? A remote, unauthenticated attacker can't trigger this because the NBD connection is initiated by the *client* (the kernel). So `RemoteTrigger` is false.
Here's the current assessment: Exploitable: False (DoS). DenialOfService: True (hung tasks). Unprivileged: False (requires root). UserNamespace: False (device nodes like `/dev/raw-gadget` or `/dev/nbd0` are not accessible in user namespaces). `VMGuestTrigger` is false. `VMHostTrigger` is false. `NetworkTrigger` is false. `RemoteTrigger` is false. `PeripheralTrigger` is true. `FilesystemTrigger` is false.
Wait, could there be a bug in `ext4`/`jbd2` itself? Let's check the locks. Specifically, let's analyze those involved in the `wait_on_buffer(bh)` call. `jbd2/sda1-8` is in `wait_on_buffer`. It holds NO locks. It is waiting for `BH_Lock` to be cleared by the block IO completion. There is no circular lock dependency between the tasks involved. No deadlock in `jbd2`. It's a pure block IO hang.
Could a bug in `virtio-blk` be to blame? Not in this stack trace. Syzkaller frequently triggers this via `raw-gadget` or `nbd`. So, since `nbd1-recv` is present, it is *highly* likely itβs NBD. That points back to a user-space block device hang (either `nbd` or `raw-gadget`). And this needs root. The worker thread `nbd1-recv` is a workqueue.
Now, could NBD be related to `
|
| 51/2 |
2026/06/01 15:08 |
tool |
read-file |
0m
Args: map[File:fs/jbd2/commit.c FirstLine:600 LineCount:100]
Results: map[Contents: 600: J_ASSERT(commit_transaction->t_nr_buffers <=
601: atomic_read(&commit_transaction->t_outstanding_credits));
602:
603: bufs = 0;
604: descriptor = NULL;
605: while (commit_transaction->t_buffers) {
606:
607: /* Find the next buffer to be journaled... */
608:
609: jh = commit_transaction->t_buffers;
610:
611: /* If we're in abort mode, we just un-journal the buffer and
612: release it. */
613:
614: if (is_journal_aborted(journal)) {
615: clear_buffer_jbddirty(jh2bh(jh));
616: JBUFFER_TRACE(jh, "journal is aborting: refile");
617: jbd2_buffer_abort_trigger(jh,
618: jh->b_frozen_data ?
619: jh->b_frozen_triggers :
620: jh->b_triggers);
621: jbd2_journal_refile_buffer(journal, jh);
622: /* If that was the last one, we need to clean up
623: * any descriptor buffers which may have been
624: * already allocated, even if we are now
625: * aborting. */
626: if (!commit_transaction->t_buffers)
627: goto start_journal_io;
628: continue;
629: }
630:
631: /* Make sure we have a descriptor block in which to
632: record the metadata buffer. */
633:
634: if (!descriptor) {
635: J_ASSERT (bufs == 0);
636:
637: jbd2_debug(4, "JBD2: get descriptor\n");
638:
639: descriptor = jbd2_journal_get_descriptor_buffer(
640: commit_transaction,
641: JBD2_DESCRIPTOR_BLOCK);
642: if (!descriptor) {
643: jbd2_journal_abort(journal, -EIO);
644: continue;
645: }
646:
647: jbd2_debug(4, "JBD2: got buffer %llu (%p)\n",
648: (unsigned long long)descriptor->b_blocknr,
649: descriptor->b_data);
650: tagp = &descriptor->b_data[sizeof(journal_header_t)];
651: space_left = descriptor->b_size -
652: sizeof(journal_header_t);
653: first_tag = 1;
654: set_buffer_jwrite(descriptor);
655: set_buffer_dirty(descriptor);
656: wbuf[bufs++] = descriptor;
657:
658: /* Record it so that we can wait for IO
659: completion later */
660: BUFFER_TRACE(descriptor, "ph3: file as descriptor");
661: jbd2_file_log_bh(&log_bufs, descriptor);
662: }
663:
664: /* Where is the buffer to be written? */
665:
666: err = jbd2_journal_next_log_block(journal, &blocknr);
667: /* If the block mapping failed, just abandon the buffer
668: and repeat this loop: we'll fall into the
669: refile-on-abort condition above. */
670: if (err) {
671: jbd2_journal_abort(journal, err);
672: continue;
673: }
674:
675: /*
676: * start_this_handle() uses t_outstanding_credits to determine
677: * the free space in the log.
678: */
679: atomic_dec(&commit_transaction->t_outstanding_credits);
680:
681: /* Bump b_count to prevent truncate from stumbling over
682: the shadowed buffer! @@@ This can go if we ever get
683: rid of the shadow pairing of buffers. */
684: atomic_inc(&jh2bh(jh)->b_count);
685:
686: /*
687: * Make a temporary IO buffer with which to write it out
688: * (this will requeue the metadata buffer to BJ_Shadow).
689: */
690: set_bit(BH_JWrite, &jh2bh(jh)->b_state);
691: JBUFFER_TRACE(jh, "ph3: write metadata");
692: escape = jbd2_journal_write_metadata_buffer(commit_transaction,
693: jh, &wbuf[bufs], blocknr);
694: jbd2_file_log_bh(&io_bufs, wbuf[bufs]);
695:
696: /* Record the new block's tag in the current descriptor
697: buffer */
698:
699: tag_flag = 0;
]
|
| 52/2 |
2026/06/01 15:08 |
llm |
expert |
0m
Model:
Tokens:
input: 75027
output: 66
thoughts: 442
Thoughts: **Analyzing the Block IO Hang in `jbd2_journal_write_metadata_buffer`**
Okay, let's break this down. My initial observation is that `jbd2_journal_write_metadata_buffer` is creating a temporary IO buffer, `wbuf[bufs]`. This `wbuf` is populated and eventually added to `io_bufs`. The crucial part comes in the subsequent loop. I see that *all* the buffers within `wbuf` β which, critically, are the same buffers also in `io_bufs` (and `log_bufs`) β are being locked, marked as clean, updated, assigned an end-IO function (`journal_end_buffer_io_sync`), and then submitted using `submit_bh`.
This confirms it. There's no possible scenario here where a buffer enters `io_bufs` and isn't subsequently submitted. Therefore, any `wait_on_buffer` call is *definitely* waiting on that `submit_bh` call to complete. It's a block IO hang, as expected.
My conclusion is that this is a block IO hang. It's almost certainly caused by a user-space emulated block device, like an NBD server or a USB mass storage device using raw-gadget, that's simply not responding to the IO requests. This leads the ext4 journal commit thread, specifically `jbd2/sda1-8` in this case, to get stuck in `wait_on_buffer`, waiting for the IO to finish. Other processes that are trying to write to the file system then hang in `do_get_write_access` because they are waiting for the journal commit to finish writing the buffer, which is indicated by the `BH_Shadow` bit.
This behavior is well-documented for user-space block devices. It's not a kernel bug, unfortunately. The attacker needs root privileges to create and mount the ext4 file system on the problematic device. This could be triggered, for instance, by a malicious USB mass storage device, exploiting a "Peripheral Trigger". This constitutes a Denial of Service, but it's not a memory corruption vulnerability.
|
| 53/2 |
2026/06/01 15:08 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 54/2 |
2026/06/01 15:08 |
llm |
expert |
0m
Model:
Tokens:
input: 76057
output: 748
thoughts: 13
Thoughts: Okay, here's the summary, formatted as you requested:
**Final Reasoning: Now We Put It All Together**
Alright, the data is in, the calculations are complete. No more adjustments needed β the outcome is fixed. Now comes the part I always enjoy: synthesizing everything into a coherent, defensible narrative. It's time to build the case, to lay out the final reasoning that connects the dots and justifies the conclusion. This isn't just a regurgitation of the data; itβs about drawing the essential linkages, weighing the nuances, and presenting a compelling argument that demonstrates a complete understanding of the topic at hand. It's about showing *why* the results are what they are, not just *that* they are. This is where the real expertise comes through β connecting evidence to the established body of knowledge, anticipating potential counterarguments, and ensuring the final analysis is both rigorous and easily understood. Let's get to work.
|
| 55/1 |
2026/06/01 15:09 |
action |
format-explanation |
0m
Results: map[Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the issue:
**Root Cause Analysis:**
The bug report shows several tasks hung in `D` state for over 143 seconds.
1. The `jbd2/sda1-8` thread (the journal commit thread for the `sda1` ext4
filesystem) is blocked in `wait_on_buffer()` within
`jbd2_journal_commit_transaction()`. It has submitted a metadata buffer to the
block layer via `submit_bh()` and is waiting for the block IO to complete (which
clears the `BH_Lock` bit).
2. Other tasks (`syz.*` and `kworker`) are blocked in `do_get_write_access()`
waiting for the `BH_Shadow` bit to be cleared on a buffer. This bit is cleared
by `journal_end_buffer_io_sync()` when the block IO for the committing
transaction completes.
This indicates a complete block IO stall on the `sda1` block device. The block
layer is not completing the submitted bios.
The presence of `nbd1-recv` workers in the lockdep output strongly suggests that
syzkaller has set up a user-space block device (like NBD, or a USB mass storage
device via `/dev/raw-gadget` backed by NBD/loop). If the user-space process
responsible for handling the IO for this block device (e.g., the syzkaller NBD
server or USB gadget emulator) stops responding, hangs, or intentionally sleeps,
the block IO will hang indefinitely. The kernel's block layer and the SCSI error
handler (which can also hang or loop if the device ignores resets) will wait for
the device, causing the filesystem mounted on it to hang.
This is a known and expected behavior when dealing with user-space emulated
block devices or failing hardware. The kernel cannot magically complete IO if
the underlying device or user-space emulator refuses to respond.
**Security Impact Assessment:**
* **Exploitable:** False. This is a pure IO hang leading to a Denial of Service
(unkillable tasks in `D` state). There is no memory corruption, use-after-free,
or out-of-bounds access involved.
* **Denial Of Service:** True. The hung tasks will trigger the `khungtaskd`
panic (if `panic_on_hung_task` is set) or simply leave unkillable processes
holding critical filesystem and memory locks (`mmap_lock`, `sb_writers`),
effectively hanging the system or the affected mount point.
* **Accessible From Unprivileged Processes & User Namespaces:** False. Creating
user-space block devices (like `/dev/nbd0`, `/dev/loop-control`, or
`/dev/raw-gadget`) requires root privileges (mode 0600, owned by root).
Furthermore, mounting an `ext4` filesystem is not permitted in unprivileged user
namespaces (`FS_USERNS_MOUNT` is not set for ext4).
* **Peripheral Trigger:** True. An attacker could physically plug in a malicious
USB mass storage device that advertises a valid partition table but then
intentionally ignores all subsequent SCSI read/write commands and bus resets. If
the system auto-mounts the device, the kernel will hang waiting for the IO to
complete, resulting in a DoS.
* **Filesystem Trigger:** False. The hang is caused by the block device failing
to complete IO requests, not by the filesystem parsing malicious data
structures.]
|