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

From: syzbot
Date: Thu Feb 06 2025 - 08:10:48 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 69e858e0b8b2 Merge tag 'uml-for-linus-6.14-rc1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=161f35f8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=36c931489897af84
dashboard link: https://syzkaller.appspot.com/bug?extid=8f1c85b6240c665f0c51
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2ed318e5efa5/disk-69e858e0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8002a1e89099/vmlinux-69e858e0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d228768d8514/bzImage-69e858e0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8f1c85b6240c665f0c51@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.13.0-syzkaller-09760-g69e858e0b8b2 #0 Not tainted
------------------------------------------------------
syz.3.973/9608 is trying to acquire lock:
ffff888061861940 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888061861940 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x499/0xd50 fs/autofs/waitq.c:164

but task is already holding lock:
ffff88803370f488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x27b/0x500 fs/kernfs/file.c:325

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&of->mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
kernfs_seq_start+0x4d/0x240 fs/kernfs/file.c:154
seq_read_iter+0x2ab/0x12b0 fs/seq_file.c:225
kernfs_fop_read_iter+0x414/0x580 fs/kernfs/file.c:279
new_sync_read fs/read_write.c:484 [inline]
vfs_read+0x886/0xbf0 fs/read_write.c:565
ksys_read+0x12b/0x250 fs/read_write.c:708
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&p->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
seq_read_iter+0xd8/0x12b0 fs/seq_file.c:182
proc_reg_read_iter+0x118/0x310 fs/proc/inode.c:295
copy_splice_read+0x61d/0xb80 fs/splice.c:365
do_splice_read fs/splice.c:985 [inline]
do_splice_read+0x282/0x370 fs/splice.c:959
splice_file_to_pipe+0x109/0x120 fs/splice.c:1295
do_sendfile+0x3fd/0xe40 fs/read_write.c:1369
__do_sys_sendfile64 fs/read_write.c:1418 [inline]
__se_sys_sendfile64 fs/read_write.c:1410 [inline]
__x64_sys_sendfile64+0x155/0x220 fs/read_write.c:1410
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&pipe->mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
pipe_write+0x166/0x1b30 fs/pipe.c:456
__kernel_write_iter+0x71f/0xa90 fs/read_write.c:612
__kernel_write+0xf6/0x140 fs/read_write.c:632
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x4ce/0xd50 fs/autofs/waitq.c:164
autofs_wait+0x10b5/0x1a30 fs/autofs/waitq.c:426
autofs_mount_wait+0x132/0x380 fs/autofs/root.c:255
autofs_d_automount+0x390/0x7f0 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x192/0x760 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x593/0x2220 fs/namei.c:1952
walk_component+0xfc/0x5b0 fs/namei.c:2120
link_path_walk.part.0.constprop.0+0x669/0xd40 fs/namei.c:2479
link_path_walk fs/namei.c:2410 [inline]
path_lookupat+0x93/0x770 fs/namei.c:2635
do_o_path fs/namei.c:3960 [inline]
path_openat+0x1754/0x2d80 fs/namei.c:3982
do_filp_open+0x20c/0x470 fs/namei.c:4016
do_sys_openat2+0x17a/0x1e0 fs/open.c:1427
do_sys_open fs/open.c:1442 [inline]
__do_sys_openat fs/open.c:1458 [inline]
__se_sys_openat fs/open.c:1453 [inline]
__x64_sys_openat+0x175/0x210 fs/open.c:1453
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&sbi->pipe_mutex){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain kernel/locking/lockdep.c:3906 [inline]
__lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x499/0xd50 fs/autofs/waitq.c:164
autofs_wait+0x10b5/0x1a30 fs/autofs/waitq.c:426
autofs_mount_wait+0x132/0x380 fs/autofs/root.c:255
autofs_d_automount+0x390/0x7f0 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x192/0x760 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x593/0x2220 fs/namei.c:1952
walk_component+0xfc/0x5b0 fs/namei.c:2120
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x17f/0x770 fs/namei.c:2636
filename_lookup+0x221/0x5f0 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xd9/0x280 block/bdev.c:1163
resume_store+0x1d8/0x460 kernel/power/hibernate.c:1247
kobj_attr_store+0x55/0x80 lib/kobject.c:840
sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0x5ae/0x1150 fs/read_write.c:679
ksys_write+0x12b/0x250 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
&sbi->pipe_mutex --> &p->lock --> &of->mutex

Possible unsafe locking scenario:

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

*** DEADLOCK ***

4 locks held by syz.3.973/9608:
#0: ffff88807d610638 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x267/0x390 fs/file.c:1192
#1: ffff888030718420 (sb_writers#9){.+.+}-{0:0}, at: ksys_write+0x12b/0x250 fs/read_write.c:731
#2: ffff88803370f488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x27b/0x500 fs/kernfs/file.c:325
#3: ffff888140ebd788 (kn->active#76){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x29e/0x500 fs/kernfs/file.c:326

stack backtrace:
CPU: 1 UID: 0 PID: 9608 Comm: syz.3.973 Not tainted 6.13.0-syzkaller-09760-g69e858e0b8b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076
check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain kernel/locking/lockdep.c:3906 [inline]
__lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x499/0xd50 fs/autofs/waitq.c:164
autofs_wait+0x10b5/0x1a30 fs/autofs/waitq.c:426
autofs_mount_wait+0x132/0x380 fs/autofs/root.c:255
autofs_d_automount+0x390/0x7f0 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x192/0x760 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x593/0x2220 fs/namei.c:1952
walk_component+0xfc/0x5b0 fs/namei.c:2120
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x17f/0x770 fs/namei.c:2636
filename_lookup+0x221/0x5f0 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xd9/0x280 block/bdev.c:1163
resume_store+0x1d8/0x460 kernel/power/hibernate.c:1247
kobj_attr_store+0x55/0x80 lib/kobject.c:840
sysfs_kf_write+0x117/0x170 fs/sysfs/file.c:139
kernfs_fop_write_iter+0x33d/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0x5ae/0x1150 fs/read_write.c:679
ksys_write+0x12b/0x250 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6d40f8cda9
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:00007f6d41def038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6d411a6160 RCX: 00007f6d40f8cda9
RDX: 0000000000000012 RSI: 00000000200000c0 RDI: 0000000000000006
RBP: 00007f6d4100e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f6d411a6160 R15: 00007ffd50927f88
</TASK>
block device autoloading is deprecated and will be removed.
PM: Image not found (code -22)

---
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