possible deadlock in mnt_want_write (5)

Status: auto-obsoleted due to no activity on 2025/04/20 18:48
Subsystems: kernfs
[Documentation on labels]
Reported-by: syzbot+64625f8c24fc389ae96d@syzkaller.appspotmail.com
First crash: 569d, last: 569d
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernfs?] possible deadlock in mnt_want_write (5) 0 (1) 2025/01/14 18:59
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in mnt_want_write (8) ext4 4 syz, C 3 38d 55d 0/29 closed as dup on 2026/06/09 14:03
linux-6.6 possible deadlock in mnt_want_write 4 1 2d05h 2d05h 0/2 upstream: reported on 2026/08/01 11:19
linux-5.15 possible deadlock in mnt_want_write missing-backport 4 syz, C done 117 979d 1231d 0/3 auto-obsoleted due to no activity on 2024/10/15 12:27
upstream possible deadlock in mnt_want_write (6) kernfs 4 1 419d 415d 0/29 auto-obsoleted due to no activity on 2025/08/08 23:21
upstream possible deadlock in mnt_want_write fs 4 syz, C done done 662 2125d 2932d 15/29 fixed on 2020/11/16 12:12
linux-6.1 possible deadlock in mnt_want_write origin:upstream missing-backport 4 syz, C done 56 980d 1224d 0/3 upstream: reported C repro on 2023/03/28 13:05
linux-4.19 possible deadlock in mnt_want_write romfs 4 syz, C 730 1245d 2663d 0/1 upstream: reported C repro on 2019/04/19 16:54
android-49 possible deadlock in mnt_want_write 4 1 2915d 2915d 0/3 auto-closed as invalid on 2019/02/22 14:57
upstream possible deadlock in mnt_want_write (4) kernfs 4 1 695d 691d 0/29 auto-obsoleted due to no activity on 2024/12/16 14:12
upstream possible deadlock in mnt_want_write (2) integrity overlayfs 4 syz, C done 867 1006d 1874d 25/29 fixed on 2023/12/21 01:43
upstream possible deadlock in mnt_want_write (3) kernfs 4 9 842d 945d 0/29 auto-obsoleted due to no activity on 2024/07/22 10:45
upstream possible deadlock in mnt_want_write (7) fs 4 3 214d 217d 0/29 auto-obsoleted due to no activity on 2026/04/11 06:22
linux-4.14 possible deadlock in mnt_want_write ubifs 4 syz, C 10467 1245d 2657d 0/1 upstream: reported C repro on 2019/04/25 05:09

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.13.0-rc6-syzkaller-00130-g2144da25584e #0 Not tainted
------------------------------------------------------
syz.5.330/7423 is trying to acquire lock:
ffff88807ef2c420 (sb_writers#5){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:515

but task is already holding lock:
ffff88805a8a2418
 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: inode_lock include/linux/fs.h:818 [inline]
 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: open_last_lookups fs/namei.c:3745 [inline]
 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: path_openat+0x89a/0x3590 fs/namei.c:3984

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       down_read+0xb1/0xa40 kernel/locking/rwsem.c:1524
       inode_lock_shared include/linux/fs.h:828 [inline]
       lookup_slow+0x45/0x70 fs/namei.c:1807
       walk_component+0x2e1/0x410 fs/namei.c:2112
       lookup_last fs/namei.c:2610 [inline]
       path_lookupat+0x16f/0x450 fs/namei.c:2634
       filename_lookup+0x2a3/0x670 fs/namei.c:2663
       kern_path+0x35/0x50 fs/namei.c:2771
       lookup_bdev+0xc5/0x290 block/bdev.c:1163
       resume_store+0x1a0/0x710 kernel/power/hibernate.c:1242
       kernfs_fop_write_iter+0x3a0/0x500 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:586 [inline]
       vfs_write+0xaeb/0xd30 fs/read_write.c:679
       ksys_write+0x18f/0x2b0 fs/read_write.c:731
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&of->mutex){+.+.}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735
       kernfs_fop_write_iter+0x1ea/0x500 fs/kernfs/file.c:325
       iter_file_splice_write+0xbfa/0x1510 fs/splice.c:743
       do_splice_from fs/splice.c:941 [inline]
       do_splice+0xd68/0x18e0 fs/splice.c:1354
       __do_splice fs/splice.c:1436 [inline]
       __do_sys_splice fs/splice.c:1639 [inline]
       __se_sys_splice+0x2e0/0x450 fs/splice.c:1621
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&pipe->mutex){+.+.}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735
       iter_file_splice_write+0x330/0x1510 fs/splice.c:687
       backing_file_splice_write+0x35a/0x570 fs/backing-file.c:315
       ovl_splice_write+0x4b8/0x630 fs/overlayfs/file.c:440
       do_splice_from fs/splice.c:941 [inline]
       do_splice+0xd68/0x18e0 fs/splice.c:1354
       __do_splice fs/splice.c:1436 [inline]
       __do_sys_splice fs/splice.c:1639 [inline]
       __se_sys_splice+0x2e0/0x450 fs/splice.c:1621
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_writers#5){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
       __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1725 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1861
       mnt_want_write+0x3f/0x90 fs/namespace.c:515
       ovl_create_object+0x13a/0x3a0 fs/overlayfs/dir.c:656
       lookup_open fs/namei.c:3649 [inline]
       open_last_lookups fs/namei.c:3748 [inline]
       path_openat+0x1c03/0x3590 fs/namei.c:3984
       do_filp_open+0x27f/0x4e0 fs/namei.c:4014
       do_sys_openat2+0x13e/0x1d0 fs/open.c:1402
       do_sys_open fs/open.c:1417 [inline]
       __do_sys_openat fs/open.c:1433 [inline]
       __se_sys_openat fs/open.c:1428 [inline]
       __x64_sys_openat+0x247/0x2a0 fs/open.c:1428
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  sb_writers#5 --> &of->mutex --> &ovl_i_mutex_dir_key[depth]

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ovl_i_mutex_dir_key[depth]);
                               lock(&of->mutex);
                               lock(&ovl_i_mutex_dir_key[depth]);
  rlock(sb_writers#5);

 *** DEADLOCK ***

2 locks held by syz.5.330/7423:
 #0: ffff888142bfa420 (sb_writers#14){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:515
 #1: ffff88805a8a2418 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: inode_lock include/linux/fs.h:818 [inline]
 #1: ffff88805a8a2418 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: open_last_lookups fs/namei.c:3745 [inline]
 #1: ffff88805a8a2418 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: path_openat+0x89a/0x3590 fs/namei.c:3984

stack backtrace:
CPU: 1 UID: 0 PID: 7423 Comm: syz.5.330 Not tainted 6.13.0-rc6-syzkaller-00130-g2144da25584e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
 percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
 __sb_start_write include/linux/fs.h:1725 [inline]
 sb_start_write+0x4d/0x1c0 include/linux/fs.h:1861
 mnt_want_write+0x3f/0x90 fs/namespace.c:515
 ovl_create_object+0x13a/0x3a0 fs/overlayfs/dir.c:656
 lookup_open fs/namei.c:3649 [inline]
 open_last_lookups fs/namei.c:3748 [inline]
 path_openat+0x1c03/0x3590 fs/namei.c:3984
 do_filp_open+0x27f/0x4e0 fs/namei.c:4014
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1402
 do_sys_open fs/open.c:1417 [inline]
 __do_sys_openat fs/open.c:1433 [inline]
 __se_sys_openat fs/open.c:1428 [inline]
 __x64_sys_openat+0x247/0x2a0 fs/open.c:1428
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd5a0185d29
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd5a1059038 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fd5a0376080 RCX: 00007fd5a0185d29
RDX: 000000000000275a RSI: 0000000020000080 RDI: ffffffffffffff9c
RBP: 00007fd5a0201b08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fd5a0376080 R15: 00007ffc67faf488
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/01/10 18:48 upstream 2144da25584e 67d7ec0a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in mnt_want_write
* Struck through repros no longer work on HEAD.