From: syzbot <syzbot+002fb7b2d0bc53bf7e75@syzkaller.appspotmail.com>
To: autofs@vger.kernel.org, linux-kernel@vger.kernel.org,
raven@themaw.net, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [autofs?] possible deadlock in anon_pipe_prefill_and_lock
Date: Fri, 18 Sep 2026 03:46:42 -0700 [thread overview]
Message-ID: <6aad1692.87c06881.1db2b3.0022.GAE@google.com> (raw)
In-Reply-To: <6aa23178.f81106d8.2ab401.0006.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: 4982d3552a3b Merge tag 'sound-7.3-rc4' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176da915580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84649d3ff8d550cb
dashboard link: https://syzkaller.appspot.com/bug?extid=002fb7b2d0bc53bf7e75
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10eda915580000
Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-4982d355.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d2afaea1fac3/vmlinux-4982d355.xz
kernel image: https://storage.googleapis.com/syzbot-assets/06e82fadea82/bzImage-4982d355.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+002fb7b2d0bc53bf7e75@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/5928 is trying to acquire lock:
ffff88802d512c60 (&pipe->mutex){+.+.}-{4:4}, at: anon_pipe_prefill_and_lock+0x16c/0x580 fs/pipe.c:165
but task is already holding lock:
ffff888036200938 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888036200938 (&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:
-> #3 (&sbi->pipe_mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__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+0xd8/0x2a0 block/bdev.c:1268
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:842
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+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&of->mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
kernfs_seq_start+0x4f/0x2a0 fs/kernfs/file.c:165
seq_read_iter+0x2c1/0x1270 fs/seq_file.c:226
kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:290
copy_splice_read+0x4ba/0xbb0 fs/splice.c:362
do_splice_read fs/splice.c:980 [inline]
do_splice_read+0x285/0x370 fs/splice.c:954
splice_file_to_pipe+0x82/0x120 fs/splice.c:1290
do_sendfile+0x366/0xe20 fs/read_write.c:1377
__do_sys_sendfile64 fs/read_write.c:1432 [inline]
__se_sys_sendfile64 fs/read_write.c:1418 [inline]
__x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1418
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&p->lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
seq_read_iter+0xe1/0x1270 fs/seq_file.c:183
kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:290
copy_splice_read+0x4ba/0xbb0 fs/splice.c:362
do_splice_read fs/splice.c:980 [inline]
do_splice_read+0x285/0x370 fs/splice.c:954
splice_file_to_pipe+0x82/0x120 fs/splice.c:1290
do_sendfile+0x366/0xe20 fs/read_write.c:1377
__do_sys_sendfile64 fs/read_write.c:1432 [inline]
__se_sys_sendfile64 fs/read_write.c:1418 [inline]
__x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1418
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&pipe->mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
anon_pipe_prefill_and_lock+0x16c/0x580 fs/pipe.c:165
anon_pipe_write+0x164/0x1b50 fs/pipe.c:534
__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
kern_path+0x37/0x50 fs/namei.c:3036
lookup_bdev+0xd8/0x2a0 block/bdev.c:1268
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:842
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+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
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 ***
locks held by syz.0.17/5928: 4, last CPU#3:
#0: ffff88802c2fc460 (sb_writers#8){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#1: ffff88802be9e080 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:336
#2: ffff88801d344878 (kn->active#67){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
#2: ffff88801d344878 (kn->active#67){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x332/0x5f0 fs/kernfs/file.c:337
#3: ffff888036200938 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
#3: ffff888036200938 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164
stack backtrace:
CPU: 3 UID: 0 PID: 5928 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
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+0x178/0x1be kernel/locking/lockdep.c:2087
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
lock_acquire kernel/locking/lockdep.c:5942 [inline]
lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
anon_pipe_prefill_and_lock+0x16c/0x580 fs/pipe.c:165
anon_pipe_write+0x164/0x1b50 fs/pipe.c:534
__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
kern_path+0x37/0x50 fs/namei.c:3036
lookup_bdev+0xd8/0x2a0 block/bdev.c:1268
resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
kobj_attr_store+0x58/0x80 lib/kobject.c:842
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+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f00df39e159
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:00007ffeff202ac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f00df625fa0 RCX: 00007f00df39e159
RDX: 0000000000000012 RSI: 0000200000000040 RDI: 0000000000000008
RBP: 00007f00df43506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f00df625fac R14: 00007f00df625fa0 R15: 00007f00df625fa0
</TASK>
PM: Image not found (code -6)
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
next prev parent reply other threads:[~2026-09-18 10:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-10 4:26 [syzbot] [autofs?] possible deadlock in anon_pipe_prefill_and_lock syzbot
2026-09-18 10:46 ` syzbot [this message]
2026-09-23 11:06 ` syzbot
2026-10-21 12:51 ` [PATCH 0/2] kernfs, autofs: fix pipe lock cycles through sysfs stores Krystian Kaniewski
2026-10-21 12:51 ` [PATCH 1/2] kernfs: do not hold of->mutex across sysfs ->store() Krystian Kaniewski
2026-10-21 12:51 ` [PATCH 2/2] autofs: do not wait for the daemon while splice holds a pipe Krystian Kaniewski
2026-10-21 21:48 ` [PATCH 0/2] kernfs, autofs: fix pipe lock cycles through sysfs stores Tejun Heo
2026-10-22 2:46 ` Ian Kent
2026-10-23 14:05 ` Krystian Kaniewski
2026-10-23 18:33 ` Tejun Heo
2026-10-26 2:03 ` Ian Kent
2026-10-26 22:07 ` Ian Kent
2026-10-26 23:11 ` Ian Kent
2026-10-27 0:46 ` Ian Kent
2026-10-27 0:57 ` Krystian Kaniewski
2026-10-28 1:21 ` Ian Kent
2026-10-27 1:06 ` Krystian Kaniewski
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