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possible deadlock in anon_pipe_write (2)

Status: upstream: reported on 2026/04/17 15:47
Subsystems: autofs
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+459d8d87e3c2a46d4102@syzkaller.appspotmail.com
First crash: 54d, last: 54d
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
f17bd302-ff4c-4474-a825-c24cb3d683e7 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in anon_pipe_write (2) 2026/05/30 01:26 2026/05/30 01:26 2026/05/30 02:09 6b4a844333e83556da95d61d7f207e7ef5cd4bc6
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [autofs?] possible deadlock in anon_pipe_write (2) 0 (1) 2026/04/17 15:47
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in anon_pipe_write autofs 4 79 137d 393d 0/29 auto-obsoleted due to no activity on 2026/03/31 06:26

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz-executor/5806 is trying to acquire lock:
ffff88807ab04868 (&pipe->mutex){+.+.}-{4:4}, at: anon_pipe_write+0x163/0x1d40 fs/pipe.c:458

but task is already holding lock:
ffff888033264948 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888033264948 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&sbi->pipe_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       autofs_write fs/autofs/waitq.c:55 [inline]
       autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164
       autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
       autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
       follow_automount fs/namei.c:1560 [inline]
       __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
       traverse_mounts fs/namei.c:1642 [inline]
       handle_mounts fs/namei.c:1744 [inline]
       step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
       step_into fs/namei.c:2149 [inline]
       walk_component fs/namei.c:2285 [inline]
       lookup_last fs/namei.c:2786 [inline]
       path_lookupat+0x58b/0xc40 fs/namei.c:2810
       filename_lookup+0x202/0x590 fs/namei.c:2839
       kern_path+0x37/0x50 fs/namei.c:3046
       lookup_bdev+0xd8/0x280 block/bdev.c:1221
       resume_store+0x1d6/0x460 kernel/power/hibernate.c:1306
       kobj_attr_store+0x58/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:352
       aio_write+0x3ba/0x920 fs/aio.c:1633
       __io_submit_one fs/aio.c:2005 [inline]
       io_submit_one+0x1142/0x1fb0 fs/aio.c:2052
       __do_sys_io_submit fs/aio.c:2111 [inline]
       __se_sys_io_submit fs/aio.c:2081 [inline]
       __x64_sys_io_submit+0x1b1/0x3a0 fs/aio.c:2081
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:343
       iter_file_splice_write+0x830/0x10a0 fs/splice.c:736
       do_splice_from fs/splice.c:936 [inline]
       do_splice+0x109c/0x1fd0 fs/splice.c:1349
       __do_splice+0x33b/0x370 fs/splice.c:1431
       __do_sys_splice fs/splice.c:1634 [inline]
       __se_sys_splice fs/splice.c:1616 [inline]
       __x64_sys_splice+0x187/0x250 fs/splice.c:1616
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&pipe->mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       anon_pipe_write+0x163/0x1d40 fs/pipe.c:458
       __kernel_write_iter+0x6b2/0x920 fs/read_write.c:621
       __kernel_write+0xf6/0x140 fs/read_write.c:641
       autofs_write fs/autofs/waitq.c:57 [inline]
       autofs_notify_daemon+0x50d/0xd90 fs/autofs/waitq.c:164
       autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
       autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
       follow_automount fs/namei.c:1560 [inline]
       __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
       traverse_mounts fs/namei.c:1642 [inline]
       handle_mounts fs/namei.c:1744 [inline]
       step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
       step_into fs/namei.c:2149 [inline]
       open_last_lookups fs/namei.c:4624 [inline]
       path_openat+0xf95/0x31a0 fs/namei.c:4833
       do_file_open+0x20e/0x430 fs/namei.c:4865
       do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
       do_sys_open fs/open.c:1372 [inline]
       __do_sys_openat fs/open.c:1388 [inline]
       __se_sys_openat fs/open.c:1383 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1383
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &pipe->mutex --> &of->mutex --> &sbi->pipe_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sbi->pipe_mutex);
                               lock(&of->mutex);
                               lock(&sbi->pipe_mutex);
  lock(&pipe->mutex);

 *** DEADLOCK ***

1 lock held by syz-executor/5806:
 #0: ffff888033264948 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
 #0: ffff888033264948 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164

stack backtrace:
CPU: 0 UID: 0 PID: 5806 Comm: syz-executor Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
 anon_pipe_write+0x163/0x1d40 fs/pipe.c:458
 __kernel_write_iter+0x6b2/0x920 fs/read_write.c:621
 __kernel_write+0xf6/0x140 fs/read_write.c:641
 autofs_write fs/autofs/waitq.c:57 [inline]
 autofs_notify_daemon+0x50d/0xd90 fs/autofs/waitq.c:164
 autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
 autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
 autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
 follow_automount fs/namei.c:1560 [inline]
 __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
 traverse_mounts fs/namei.c:1642 [inline]
 handle_mounts fs/namei.c:1744 [inline]
 step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
 step_into fs/namei.c:2149 [inline]
 open_last_lookups fs/namei.c:4624 [inline]
 path_openat+0xf95/0x31a0 fs/namei.c:4833
 do_file_open+0x20e/0x430 fs/namei.c:4865
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f757039bb3c
Code: 4c 89 54 24 18 41 89 f2 41 83 e2 40 75 40 89 f0 f7 d0 a9 00 00 41 00 74 35 89 f2 b8 01 01 00 00 48 89 fe bf 9c ff ff ff 0f 05 <48> 3d 00 f0 ff ff 77 44 48 8b 54 24 18 64 48 2b 14 25 28 00 00 00
RSP: 002b:00007ffe92381580 EFLAGS: 00000206 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f7570432048 RCX: 00007f757039bb3c
RDX: 0000000000090800 RSI: 00007ffe92382790 RDI: 00000000ffffff9c
RBP: 00007ffe92382790 R08: 00007ffe92383790 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000206 R12: 00007ffe92382790
R13: 00007f7570432048 R14: 00000000000d5761 R15: 00007ffe92384950
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/13 15:36 upstream 028ef9c96e96 9530ccf9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in anon_pipe_write
* Struck through repros no longer work on HEAD.