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INFO: task hung in lookup_slow

Status: premoderation: reported C repro on 2025/07/13 18:29
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+bacc67e5e829964158be@syzkaller.appspotmail.com
First crash: 5d18h, last: 5d04h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/07/14 lts (merge base) e0e2f7824338 C [report] INFO: task hung in lookup_slow
2025/07/14 upstream (ToT) 347e9f5043c8 C [report] INFO: task hung in lookup_slow
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in lookup_slow (2) fs 1 2 2152d 2164d 0/29 auto-closed as invalid on 2019/11/26 02:54
upstream INFO: task hung in lookup_slow exfat 1 148 2373d 2666d 0/29 closed as dup on 2018/09/08 15:36
linux-6.1 INFO: task hung in lookup_slow origin:upstream missing-backport 1 C inconclusive 26 69d 461d 0/3 upstream: reported C repro on 2024/04/14 05:59
linux-5.15 INFO: task hung in lookup_slow (2) missing-backport origin:upstream 1 C error 53 8d13h 460d 0/3 upstream: reported C repro on 2024/04/15 04:02
upstream INFO: task hung in lookup_slow (3) fs 1 C unreliable 1857 40m 981d 0/29 upstream: reported C repro on 2022/11/11 00:21
android-49 INFO: task hung in lookup_slow 1 syz 36 2178d 2288d 0/3 public: reported syz repro on 2019/04/14 08:51
linux-4.14 INFO: task hung in lookup_slow 1 C error 1 1051d 1081d 0/1 upstream: reported C repro on 2022/08/03 08:46
linux-4.19 INFO: task hung in lookup_slow 1 1 1860d 1860d 0/1 auto-closed as invalid on 2020/10/13 00:17
linux-5.15 INFO: task hung in lookup_slow 1 2 824d 829d 0/3 auto-obsoleted due to no activity on 2023/08/15 05:05

Sample crash report:
INFO: task syz-executor305:300 blocked for more than 122 seconds.
      Not tainted 6.12.30-syzkaller-g21ed84930c16 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor305 state:D stack:0     pid:300   tgid:297   ppid:296    flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5947 [inline]
 __schedule+0x132b/0x1e00 kernel/sched/core.c:7775
 __schedule_loop kernel/sched/core.c:7856 [inline]
 schedule+0xc6/0x240 kernel/sched/core.c:7871
 schedule_preempt_disabled+0x14/0x30 kernel/sched/core.c:7928
 rwsem_down_read_slowpath+0x70d/0x1240 kernel/locking/rwsem.c:1124
 __down_read_common kernel/locking/rwsem.c:1305 [inline]
 __down_read kernel/locking/rwsem.c:1318 [inline]
 down_read+0x8f/0xe0 kernel/locking/rwsem.c:1595
 inode_lock_shared include/linux/fs.h:825 [inline]
 lookup_slow+0x4a/0x80 fs/namei.c:1748
 walk_component+0x302/0x440 fs/namei.c:2053
 lookup_last fs/namei.c:2556 [inline]
 path_lookupat+0x180/0x4a0 fs/namei.c:2580
 filename_lookup+0x1f5/0x520 fs/namei.c:2609
 user_path_at+0x42/0x60 fs/namei.c:3016
 do_mount fs/namespace.c:3856 [inline]
 __do_sys_mount fs/namespace.c:4069 [inline]
 __se_sys_mount+0x288/0x480 fs/namespace.c:4046
 __x64_sys_mount+0xc3/0xf0 fs/namespace.c:4046
 x64_sys_call+0x2021/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x58/0xf0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f64593eb829
RSP: 002b:00007f6459377218 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f64594753f8 RCX: 00007f64593eb829
RDX: 0000000000000000 RSI: 0000200000000040 RDI: 0000000000000000
RBP: 00007f64594753f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000200000 R11: 0000000000000246 R12: 00007f645944207c
R13: 0000200000000100 R14: 0000200000000040 R15: 00007fff461a5928
 </TASK>
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 37 Comm: khungtaskd Not tainted 6.12.30-syzkaller-g21ed84930c16 #0 fa4558fba7fa11aa57b2c84caea5bf67b39b1b5f
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x10c/0x190 lib/dump_stack.c:120
 dump_stack+0x19/0x20 lib/dump_stack.c:129
 nmi_cpu_backtrace+0x2bf/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x142/0x2c0 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:41
 trigger_all_cpu_backtrace include/linux/nmi.h:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:229 [inline]
 watchdog+0xd8f/0xed0 kernel/hung_task.c:385
 kthread+0x2c7/0x370 kernel/kthread.c:389
 ret_from_fork+0x64/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.12.30-syzkaller-g21ed84930c16 #0 fa4558fba7fa11aa57b2c84caea5bf67b39b1b5f
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:rcu_preempt_read_enter kernel/rcu/tree_plugin.h:390 [inline]
RIP: 0010:__rcu_read_lock+0x20/0x60 kernel/rcu/tree_plugin.h:413
Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 48 89 e5 53 65 48 8b 1c 25 40 e9 04 00 48 81 c3 c4 04 00 00 48 89 d8 48 c1 e8 03 <48> b9 00 00 00 00 00 fc ff df 0f b6 04 08 84 c0 75 0a ff 03 5b 5d
RSP: 0018:ffffc90000007cc8 EFLAGS: 00000a03
RAX: 1ffffffff0e42b40 RBX: ffffffff87215a04 RCX: dffffc0000000000
RDX: 0000000000000100 RSI: 0000000000000001 RDI: ffff8881f6e4f7c0
RBP: ffffc90000007cd0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000fb0 R12: ffff8881f6e4f7c0
R13: dffffc0000000000 R14: 1ffff1103edca07d R15: 1ffff92000000fac
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556f9f2370 CR3: 000000010b72a000 CR4: 00000000003526b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 rcu_read_lock include/linux/rcupdate.h:847 [inline]
 sched_balance_domains+0x18e/0xa10 kernel/sched/fair.c:12442
 _nohz_idle_balance+0x3e3/0x5a0 kernel/sched/fair.c:12922
 nohz_idle_balance kernel/sched/fair.c:12965 [inline]
 sched_balance_softirq+0x8a/0x170 kernel/sched/fair.c:13193
 handle_softirqs+0x1ae/0x630 kernel/softirq.c:603
 __do_softirq kernel/softirq.c:641 [inline]
 invoke_softirq kernel/softirq.c:458 [inline]
 __irq_exit_rcu+0x48/0xc0 kernel/softirq.c:690
 irq_exit_rcu+0xd/0x30 kernel/softirq.c:702
 instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
 sysvec_call_function_single+0x7f/0x90 arch/x86/kernel/smp.c:266
 </IRQ>
 <TASK>
 asm_sysvec_call_function_single+0x1f/0x30 arch/x86/include/asm/idtentry.h:709
RIP: 0010:pv_native_safe_halt+0x17/0x20 arch/x86/kernel/paravirt.c:106
Code: cc cc cc b8 9f ca 39 73 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 73 8c 41 00 f3 0f 1e fa 55 48 89 e5 fb f4 <5d> e9 83 57 02 00 cc cc cc b8 00 00 00 00 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff87207da0 EFLAGS: 000002c6
RAX: ffff8881f6e00000 RBX: ffffffff87215540 RCX: ffffffff8585c00e
RDX: 0000000000000001 RSI: 0000000000000004 RDI: 0000000000021324
RBP: ffffffff87207da0 R08: ffff8881f6e39733 R09: 1ffff1103edc72e6
R10: dffffc0000000000 R11: ffffed103edc72e7 R12: 1ffffffff0e42aa8
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff87ca7b28
 arch_safe_halt arch/x86/include/asm/paravirt.h:112 [inline]
 default_idle+0x17/0x30 arch/x86/kernel/process.c:748
 arch_cpu_idle+0xd/0x20 arch/x86/kernel/process.c:785
 default_idle_call+0x3f/0x80 kernel/sched/idle.c:117
 cpuidle_idle_call kernel/sched/idle.c:185 [inline]
 do_idle+0x1a0/0x470 kernel/sched/idle.c:326
 cpu_startup_entry+0x48/0x70 kernel/sched/idle.c:424
 rest_init+0x10b/0x130 init/main.c:748
 start_kernel+0x46a/0x4bb init/main.c:1135
 x86_64_start_reservations+0x2e/0x30 arch/x86/kernel/head64.c:507
 x86_64_start_kernel+0x6a/0x7b arch/x86/kernel/head64.c:488
 common_startup_64+0x13b/0x157
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/07/14 08:39 android16-6.12 21ed84930c16 3cda49cf .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in lookup_slow
2025/07/14 03:58 android16-6.12 21ed84930c16 3cda49cf .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in lookup_slow
2025/07/13 23:16 android16-6.12 21ed84930c16 3cda49cf .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in lookup_slow
2025/07/13 18:28 android16-6.12 21ed84930c16 3cda49cf .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in lookup_slow
* Struck through repros no longer work on HEAD.