From: syzbot <syzbot+1075f6dc93f398c1857e@syzkaller.appspotmail.com>
To: dmitry.torokhov@gmail.com, driver-core@lists.linux.dev,
gregkh@linuxfoundation.org, linux-input@vger.kernel.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com, tj@kernel.org
Subject: Re: [syzbot] [input?] possible deadlock in __kernfs_remove (3)
Date: Sat, 22 Aug 2026 20:23:30 -0700 [thread overview]
Message-ID: <6a8a67b2.ae6ddae5.3da009.0060.GAE@google.com> (raw)
In-Reply-To: <699fe31c.050a0220.2fcbed.0002.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: 66fb95a52111 Merge tag 'caps-pr-20260820' of git://git.ker..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=11ca4625580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b0978f5ed2905b98
dashboard link: https://syzkaller.appspot.com/bug?extid=1075f6dc93f398c1857e
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=10815549580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e7d9049723b0/disk-66fb95a5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a04d6efe59a0/vmlinux-66fb95a5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/81e3f2b9c049/bzImage-66fb95a5.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1075f6dc93f398c1857e@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6104 is trying to acquire lock:
ffff888035f1b008 (kn->active#59){++++}-{0:0}, at: __kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579
but task is already holding lock:
ffffffff904d00c0 (serio_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
ffffffff904d00c0 (serio_mutex){+.+.}-{4:4}, at: serio_unregister_port+0x1b/0x40 drivers/input/serio/serio.c:677
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (serio_mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
class_mutex_intr_constructor include/linux/mutex.h:255 [inline]
drvctl_store+0x3c/0x350 drivers/input/serio/serio.c:360
dev_attr_store+0x58/0x80 drivers/base/core.c:2509
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
-> #0 (kn->active#59){++++}-{0:0}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
kernfs_drain+0x4f0/0x600 fs/kernfs/dir.c:532
__kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579
kernfs_remove_by_name_ns+0x7c/0x120 fs/kernfs/dir.c:1797
kernfs_remove_by_name include/linux/kernfs.h:644 [inline]
remove_files+0x96/0x1c0 fs/sysfs/group.c:28
sysfs_remove_group+0x8b/0x1b0 fs/sysfs/group.c:328
sysfs_remove_groups fs/sysfs/group.c:352 [inline]
sysfs_remove_groups+0x60/0xb0 fs/sysfs/group.c:344
device_remove_groups drivers/base/core.c:2918 [inline]
device_remove_attrs+0x192/0x290 drivers/base/core.c:3048
device_del+0x36e/0x9b0 drivers/base/core.c:3964
serio_destroy_port+0x476/0x590 drivers/input/serio/serio.c:543
serio_unregister_port+0x2b/0x40 drivers/input/serio/serio.c:680
userio_char_release+0x91/0xe0 drivers/input/serio/userio.c:105
__fput+0x3ff/0xb50 fs/file_table.c:512
task_work_run+0x150/0x240 kernel/task_work.c:233
ptrace_notify+0xf3/0x120 kernel/signal.c:2531
ptrace_report_syscall include/linux/ptrace.h:416 [inline]
ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
arch_ptrace_report_syscall_exit include/linux/entry-common.h:233 [inline]
syscall_exit_work include/linux/entry-common.h:266 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:297 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:334 [inline]
do_syscall_64+0x5e7/0x790 arch/x86/entry/syscall_64.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(serio_mutex);
lock(kn->active#59);
lock(serio_mutex);
lock(kn->active#59);
*** DEADLOCK ***
locks held by syz.0.17/6104: 1, last CPU#1:
#0: ffffffff904d00c0 (serio_mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
#0: ffffffff904d00c0 (serio_mutex){+.+.}-{4:4}, at: serio_unregister_port+0x1b/0x40 drivers/input/serio/serio.c:677
stack backtrace:
CPU: 1 UID: 0 PID: 6104 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
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+0x178/0x1be kernel/locking/lockdep.c:2059
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
kernfs_drain+0x4f0/0x600 fs/kernfs/dir.c:532
__kernfs_remove+0x34c/0xb80 fs/kernfs/dir.c:1579
kernfs_remove_by_name_ns+0x7c/0x120 fs/kernfs/dir.c:1797
kernfs_remove_by_name include/linux/kernfs.h:644 [inline]
remove_files+0x96/0x1c0 fs/sysfs/group.c:28
sysfs_remove_group+0x8b/0x1b0 fs/sysfs/group.c:328
sysfs_remove_groups fs/sysfs/group.c:352 [inline]
sysfs_remove_groups+0x60/0xb0 fs/sysfs/group.c:344
device_remove_groups drivers/base/core.c:2918 [inline]
device_remove_attrs+0x192/0x290 drivers/base/core.c:3048
device_del+0x36e/0x9b0 drivers/base/core.c:3964
serio_destroy_port+0x476/0x590 drivers/input/serio/serio.c:543
serio_unregister_port+0x2b/0x40 drivers/input/serio/serio.c:680
userio_char_release+0x91/0xe0 drivers/input/serio/userio.c:105
__fput+0x3ff/0xb50 fs/file_table.c:512
task_work_run+0x150/0x240 kernel/task_work.c:233
ptrace_notify+0xf3/0x120 kernel/signal.c:2531
ptrace_report_syscall include/linux/ptrace.h:416 [inline]
ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
arch_ptrace_report_syscall_exit include/linux/entry-common.h:233 [inline]
syscall_exit_work include/linux/entry-common.h:266 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:297 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:334 [inline]
do_syscall_64+0x5e7/0x790 arch/x86/entry/syscall_64.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f094979e0d9
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:00007ffca1bdeb48 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f0949a27da0 RCX: 00007f094979e0d9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f0949a27da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007f0949a27cb0 R11: 0000000000000246 R12: 000000000001aa1e
R13: 00007f0949a25fac R14: 000000000001a7d2 R15: 00007ffca1bdec50
</TASK>
---
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.
prev parent reply other threads:[~2026-08-23 3:23 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-26 6:07 [syzbot] [kernfs?] possible deadlock in __kernfs_remove (3) syzbot
2026-08-23 3:23 ` syzbot [this message]
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