[syzbot] [autofs?] possible deadlock in anon_pipe_write (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 028ef9c96e96 Linux 7.0
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=147210ce580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5a3e5e8c17cc174e
dashboard link: https://syzkaller.appspot.com/bug?extid=459d8d87e3c2a46d4102
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ec3fc4ab21e9/disk-028ef9c9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/edc0fd5a0fd3/vmlinux-028ef9c9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c5a57bcdac7/bzImage-028ef9c9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+459d8d...@syzkaller.appspotmail.com

======================================================
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>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup