[syzbot] [autofs?] possible deadlock in autofs_notify_daemon (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0131b508c0e2 Merge tag 'ntfs-for-7.2-rc6' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10daee32580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=2b1c8c58f62458852a54
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/237b6b227f6e/disk-0131b508.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/90a5294c2a5d/vmlinux-0131b508.xz
kernel image: https://storage.googleapis.com/syzbot-assets/54d17924c110/bzImage-0131b508.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2b1c8c...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.4.2436/14866 is trying to acquire lock:
ffff8880243be138 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff8880243be138 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164

but task is already holding lock:
ffff888055e70880 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&of->mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
iter_file_splice_write+0x830/0x10b0 fs/splice.c:736
do_splice_from fs/splice.c:936 [inline]
do_splice+0x109c/0x1f90 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+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&pipe->mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
anon_pipe_write+0x25e/0x1d90 fs/pipe.c:553
__kernel_write_iter+0x6bb/0x930 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:256
autofs_d_automount+0x490/0x950 fs/autofs/root.c:410
follow_automount fs/namei.c:1565 [inline]
__traverse_mounts+0x1b9/0x8a0 fs/namei.c:1618
traverse_mounts fs/namei.c:1647 [inline]
handle_mounts fs/namei.c:1749 [inline]
step_into_slowpath+0xb7e/0xf90 fs/namei.c:2104
step_into fs/namei.c:2152 [inline]
walk_component fs/namei.c:2288 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x58b/0xc40 fs/namei.c:2813
filename_lookup+0x202/0x590 fs/namei.c:2842
do_fchownat+0xe6/0x1f0 fs/open.c:800
__do_sys_lchown fs/open.c:829 [inline]
__se_sys_lchown fs/open.c:827 [inline]
__x64_sys_lchown+0x7e/0xc0 fs/open.c:827
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&sbi->pipe_mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
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:256
autofs_d_automount+0x490/0x950 fs/autofs/root.c:410
follow_automount fs/namei.c:1565 [inline]
__traverse_mounts+0x1b9/0x8a0 fs/namei.c:1618
traverse_mounts fs/namei.c:1647 [inline]
handle_mounts fs/namei.c:1749 [inline]
step_into_slowpath+0xb7e/0xf90 fs/namei.c:2104
step_into fs/namei.c:2152 [inline]
walk_component fs/namei.c:2288 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x58b/0xc40 fs/namei.c:2813
filename_lookup+0x202/0x590 fs/namei.c:2842
kern_path+0x37/0x50 fs/namei.c:3036
lookup_bdev+0xd8/0x280 block/bdev.c:1208
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:840
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 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:
&sbi->pipe_mutex --> &pipe->mutex --> &of->mutex

Possible unsafe locking scenario:

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

*** DEADLOCK ***

4 locks held by syz.4.2436/14866:
#0: ffff888057e055f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259
#1: ffff88807f95c450 (sb_writers#8){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#2: ffff888055e70880 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
#3: ffff88801f287698 (kn->active#70){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
#3: ffff88801f287698 (kn->active#70){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x332/0x5f0 fs/kernfs/file.c:337

stack backtrace:
CPU: 0 UID: 0 PID: 14866 Comm: syz.4.2436 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
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:256
autofs_d_automount+0x490/0x950 fs/autofs/root.c:410
follow_automount fs/namei.c:1565 [inline]
__traverse_mounts+0x1b9/0x8a0 fs/namei.c:1618
traverse_mounts fs/namei.c:1647 [inline]
handle_mounts fs/namei.c:1749 [inline]
step_into_slowpath+0xb7e/0xf90 fs/namei.c:2104
step_into fs/namei.c:2152 [inline]
walk_component fs/namei.c:2288 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x58b/0xc40 fs/namei.c:2813
filename_lookup+0x202/0x590 fs/namei.c:2842
kern_path+0x37/0x50 fs/namei.c:3036
lookup_bdev+0xd8/0x280 block/bdev.c:1208
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:840
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc8e1d9e019
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc8e2c6a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc8e2026360 RCX: 00007fc8e1d9e019
RDX: 0000000000000012 RSI: 0000200000000040 RDI: 000000000000000c
RBP: 00007fc8e1e3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc8e20263f8 R14: 00007fc8e2026360 R15: 00007ffe9c4403d8
</TASK>
PM: Image not found (code -22)


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