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possible deadlock in lookup_slow

Status: upstream: reported on 2025/01/31 18:32
Reported-by: syzbot+6aa8d2e821f9d40fbe56@syzkaller.appspotmail.com
First crash: 52d, last: 52d
▶ ▼ Similar bugs (7)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in lookup_slow (3) kernfs 343 10d 614d 0/28 upstream: reported on 2023/07/19 13:17
linux-5.15 possible deadlock in lookup_slow 11 570d 741d 0/3 auto-obsoleted due to no activity on 2023/12/11 13:10
linux-4.19 possible deadlock in lookup_slow 22 1744d 2170d 0/1 auto-closed as invalid on 2020/10/12 22:59
upstream possible deadlock in lookup_slow fs 139 2130d 2372d 0/28 auto-closed as invalid on 2019/10/25 08:42
linux-5.15 possible deadlock in lookup_slow (2) origin:lts-only C 86 8d07h 467d 0/3 upstream: reported C repro on 2023/12/13 22:35
linux-4.14 possible deadlock in lookup_slow C 2027 749d 2040d 0/1 upstream: reported C repro on 2019/08/24 01:53
upstream possible deadlock in lookup_slow (2) fs 7 1899d 1943d 0/28 auto-closed as invalid on 2020/05/11 09:17

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.1.127-syzkaller #0 Not tainted
------------------------------------------------------
udevd/4848 is trying to acquire lock:
ffff0000c04a0e08 (&type->i_mutex_dir_key#3){++++}-{3:3}, at: inode_lock_shared include/linux/fs.h:768 [inline]
ffff0000c04a0e08 (&type->i_mutex_dir_key#3){++++}-{3:3}, at: lookup_slow+0x50/0x84 fs/namei.c:1706

but task is already holding lock:
ffff0000f36fece0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add+0x6e8/0x1d08 fs/btrfs/volumes.c:860

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x190/0x21a0 kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       btrfs_run_dev_stats+0xf4/0xea4 fs/btrfs/volumes.c:8058
       commit_cowonly_roots+0x1a4/0x740 fs/btrfs/transaction.c:1295
       btrfs_commit_transaction+0x1228/0x2cd4 fs/btrfs/transaction.c:2425
       btrfs_rebuild_free_space_tree+0x2e8/0x6dc fs/btrfs/free-space-tree.c:1338
       btrfs_start_pre_rw_mount+0x2cc/0x65c fs/btrfs/disk-io.c:3238
       open_ctree+0x1e40/0x2340 fs/btrfs/disk-io.c:3835
       btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1469
       btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1835
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       fc_mount fs/namespace.c:1043 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1073
       btrfs_mount+0x330/0x9c8 fs/btrfs/super.c:1895
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       do_new_mount+0x278/0x8fc fs/namespace.c:3056
       path_mount+0x590/0xe5c fs/namespace.c:3386
       do_mount fs/namespace.c:3399 [inline]
       __do_sys_mount fs/namespace.c:3607 [inline]
       __se_sys_mount fs/namespace.c:3584 [inline]
       __arm64_sys_mount+0x45c/0x594 fs/namespace.c:3584
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #5 (&fs_info->reloc_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x190/0x21a0 kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       btrfs_record_root_in_trans fs/btrfs/transaction.c:486 [inline]
       start_transaction+0x47c/0x1110 fs/btrfs/transaction.c:728
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:764
       btrfs_create_common+0x198/0x2b8 fs/btrfs/inode.c:6778
       btrfs_create+0x104/0x128 fs/btrfs/inode.c:6824
       lookup_open fs/namei.c:3482 [inline]
       open_last_lookups fs/namei.c:3550 [inline]
       path_openat+0xeac/0x2548 fs/namei.c:3780
       do_filp_open+0x1bc/0x3cc fs/namei.c:3810
       do_sys_openat2+0x128/0x3e0 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __arm64_sys_openat+0x1f0/0x240 fs/open.c:1345
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #4 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x194/0xb6c fs/btrfs/transaction.c:301
       start_transaction+0x7b8/0x1110 fs/btrfs/transaction.c:665
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:764
       btrfs_rebuild_free_space_tree+0xb4/0x6dc fs/btrfs/free-space-tree.c:1311
       btrfs_start_pre_rw_mount+0x2cc/0x65c fs/btrfs/disk-io.c:3238
       open_ctree+0x1e40/0x2340 fs/btrfs/disk-io.c:3835
       btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1469
       btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1835
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       fc_mount fs/namespace.c:1043 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1073
       btrfs_mount+0x330/0x9c8 fs/btrfs/super.c:1895
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       do_new_mount+0x278/0x8fc fs/namespace.c:3056
       path_mount+0x590/0xe5c fs/namespace.c:3386
       do_mount fs/namespace.c:3399 [inline]
       __do_sys_mount fs/namespace.c:3607 [inline]
       __se_sys_mount fs/namespace.c:3584 [inline]
       __arm64_sys_mount+0x45c/0x594 fs/namespace.c:3584
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #3 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5376 [inline]
       lock_release+0x364/0xa50 kernel/locking/lockdep.c:5682
       percpu_up_read include/linux/percpu-rwsem.h:99 [inline]
       __sb_end_write include/linux/fs.h:1886 [inline]
       sb_end_intwrite+0x58/0x3fc include/linux/fs.h:1942
       __btrfs_end_transaction+0x314/0x75c fs/btrfs/transaction.c:1015
       btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1049
       btrfs_dirty_inode+0x188/0x1c0 fs/btrfs/inode.c:6284
       btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6312
       inode_update_time fs/inode.c:1958 [inline]
       __file_update_time+0xc0/0x21c fs/inode.c:2147
       file_update_time+0x2cc/0x348 fs/inode.c:2178
       btrfs_page_mkwrite+0x3fc/0xcac fs/btrfs/inode.c:8597
       do_page_mkwrite+0x144/0x37c mm/memory.c:3009
       wp_page_shared+0x148/0x550 mm/memory.c:3358
       do_wp_page+0xcbc/0xf44 mm/memory.c:3508
       handle_pte_fault mm/memory.c:5047 [inline]
       __handle_mm_fault mm/memory.c:5171 [inline]
       handle_mm_fault+0x19a4/0x3d38 mm/memory.c:5292
       __do_page_fault arch/arm64/mm/fault.c:499 [inline]
       do_page_fault+0x330/0x890 arch/arm64/mm/fault.c:583
       do_mem_abort+0x74/0x200 arch/arm64/mm/fault.c:803
       el0_da+0x70/0x184 arch/arm64/kernel/entry-common.c:515
       el0t_64_sync_handler+0xcc/0xf0 arch/arm64/kernel/entry-common.c:658
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #2 (sb_pagefaults#2){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1891 [inline]
       sb_start_pagefault include/linux/fs.h:1995 [inline]
       btrfs_page_mkwrite+0x1dc/0xcac fs/btrfs/inode.c:8581
       do_page_mkwrite+0x144/0x37c mm/memory.c:3009
       wp_page_shared+0x148/0x550 mm/memory.c:3358
       do_wp_page+0xcbc/0xf44 mm/memory.c:3508
       handle_pte_fault mm/memory.c:5047 [inline]
       __handle_mm_fault mm/memory.c:5171 [inline]
       handle_mm_fault+0x19a4/0x3d38 mm/memory.c:5292
       __do_page_fault arch/arm64/mm/fault.c:499 [inline]
       do_page_fault+0x330/0x890 arch/arm64/mm/fault.c:583
       do_mem_abort+0x74/0x200 arch/arm64/mm/fault.c:803
       el0_da+0x70/0x184 arch/arm64/kernel/entry-common.c:515
       el0t_64_sync_handler+0xcc/0xf0 arch/arm64/kernel/entry-common.c:658
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (&mm->mmap_lock){++++}-{3:3}:
       __might_fault+0xc4/0x124 mm/memory.c:5851
       filldir64+0x2d4/0x948 fs/readdir.c:335
       dir_emit include/linux/fs.h:3693 [inline]
       call_filldir fs/ext4/dir.c:544 [inline]
       ext4_dx_readdir fs/ext4/dir.c:620 [inline]
       ext4_readdir+0x2ba4/0x3388 fs/ext4/dir.c:142
       iterate_dir+0x1f4/0x4ec
       __do_sys_getdents64 fs/readdir.c:369 [inline]
       __se_sys_getdents64 fs/readdir.c:354 [inline]
       __arm64_sys_getdents64+0x1c4/0x4a0 fs/readdir.c:354
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #0 (&type->i_mutex_dir_key#3){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x3338/0x7680 kernel/locking/lockdep.c:5049
       lock_acquire+0x26c/0x7cc kernel/locking/lockdep.c:5662
       down_read+0x64/0x308 kernel/locking/rwsem.c:1520
       inode_lock_shared include/linux/fs.h:768 [inline]
       lookup_slow+0x50/0x84 fs/namei.c:1706
       walk_component+0x280/0x36c fs/namei.c:1998
       lookup_last fs/namei.c:2455 [inline]
       path_lookupat+0x13c/0x3d0 fs/namei.c:2479
       filename_lookup+0x1d4/0x4e0 fs/namei.c:2508
       kern_path+0x48/0x6c fs/namei.c:2606
       is_same_device fs/btrfs/volumes.c:695 [inline]
       device_list_add+0x1258/0x1d08 fs/btrfs/volumes.c:928
       btrfs_scan_one_device+0x3c8/0x61c fs/btrfs/volumes.c:1461
       btrfs_control_ioctl+0x144/0x388 fs/btrfs/super.c:2519
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl fs/ioctl.c:856 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

Chain exists of:
  &type->i_mutex_dir_key#3 --> &fs_info->reloc_mutex --> &fs_devs->device_list_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fs_devs->device_list_mutex);
                               lock(&fs_info->reloc_mutex);
                               lock(&fs_devs->device_list_mutex);
  lock(&type->i_mutex_dir_key#3);

 *** DEADLOCK ***

2 locks held by udevd/4848:
 #0: ffff800016197508 (uuid_mutex){+.+.}-{3:3}, at: btrfs_control_ioctl+0x130/0x388 fs/btrfs/super.c:2518
 #1: ffff0000f36fece0 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add+0x6e8/0x1d08 fs/btrfs/volumes.c:860

stack backtrace:
CPU: 0 PID: 4848 Comm: udevd Not tainted 6.1.127-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2048
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x3338/0x7680 kernel/locking/lockdep.c:5049
 lock_acquire+0x26c/0x7cc kernel/locking/lockdep.c:5662
 down_read+0x64/0x308 kernel/locking/rwsem.c:1520
 inode_lock_shared include/linux/fs.h:768 [inline]
 lookup_slow+0x50/0x84 fs/namei.c:1706
 walk_component+0x280/0x36c fs/namei.c:1998
 lookup_last fs/namei.c:2455 [inline]
 path_lookupat+0x13c/0x3d0 fs/namei.c:2479
 filename_lookup+0x1d4/0x4e0 fs/namei.c:2508
 kern_path+0x48/0x6c fs/namei.c:2606
 is_same_device fs/btrfs/volumes.c:695 [inline]
 device_list_add+0x1258/0x1d08 fs/btrfs/volumes.c:928
 btrfs_scan_one_device+0x3c8/0x61c fs/btrfs/volumes.c:1461
 btrfs_control_ioctl+0x144/0x388 fs/btrfs/super.c:2519
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x168 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
BTRFS info: devid 1 device path file0 changed to /dev/loop3 scanned by udevd (4848)

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/01/31 18:31 linux-6.1.y 75cefdf153f5 aa47157c .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in lookup_slow
* Struck through repros no longer work on HEAD.