[syzbot] [sound?] possible deadlock in snd_seq_deliver_event (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fc02acf6ac0c Merge tag 'platform-drivers-x86-v7.2-4' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17a0b8c6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=d4d7ac4a87bb2d52a822
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/67251350dd03/disk-fc02acf6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e4edd57a8c61/vmlinux-fc02acf6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/04ff166cc853/bzImage-fc02acf6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d4d7ac...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/1:3/5615 is trying to acquire lock:
ffff888032c85128 (&grp->list_lock){.+.+}-{3:3}, at: __deliver_to_subscribers sound/core/seq/seq_clientmgr.c:723 [inline]
ffff888032c85128 (&grp->list_lock){.+.+}-{3:3}, at: deliver_to_subscribers sound/core/seq/seq_clientmgr.c:763 [inline]
ffff888032c85128 (&grp->list_lock){.+.+}-{3:3}, at: snd_seq_deliver_event+0x230/0x860 sound/core/seq/seq_clientmgr.c:813

but task is already holding lock:
ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: __deliver_to_subscribers sound/core/seq/seq_clientmgr.c:723 [inline]
ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: deliver_to_subscribers sound/core/seq/seq_clientmgr.c:763 [inline]
ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: snd_seq_deliver_event+0x230/0x860 sound/core/seq/seq_clientmgr.c:813

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&grp->list_lock);
lock(&grp->list_lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kworker/1:3/5615:
#0: ffff88801bc0f140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
#1: ffffc900039c7d08 ((work_completion)(&runtime->event_work)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
#2: ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: __deliver_to_subscribers sound/core/seq/seq_clientmgr.c:723 [inline]
#2: ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: deliver_to_subscribers sound/core/seq/seq_clientmgr.c:763 [inline]
#2: ffff8880269b0128 (&grp->list_lock){.+.+}-{3:3}, at: snd_seq_deliver_event+0x230/0x860 sound/core/seq/seq_clientmgr.c:813

stack backtrace:
CPU: 1 UID: 0 PID: 5615 Comm: kworker/1:3 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: events snd_rawmidi_input_event_work
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_deadlock_bug.cold+0xbd/0xca kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain kernel/locking/lockdep.c:3895 [inline]
__lock_acquire+0x1256/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__raw_read_lock include/linux/rwlock_api_smp.h:163 [inline]
_raw_read_lock+0x5f/0x70 kernel/locking/spinlock.c:232
__deliver_to_subscribers sound/core/seq/seq_clientmgr.c:723 [inline]
deliver_to_subscribers sound/core/seq/seq_clientmgr.c:763 [inline]
snd_seq_deliver_event+0x230/0x860 sound/core/seq/seq_clientmgr.c:813
snd_seq_kernel_client_dispatch+0x16f/0x1b0 sound/core/seq/seq_clientmgr.c:2439
queue_broadcast_event.isra.0+0x143/0x1b0 sound/core/seq/seq_queue.c:585
snd_seq_queue_process_event sound/core/seq/seq_queue.c:634 [inline]
snd_seq_control_queue+0x709/0xb70 sound/core/seq/seq_queue.c:659
__snd_seq_deliver_single_event sound/core/seq/seq_clientmgr.c:626 [inline]
__snd_seq_deliver_single_event+0x127/0x1c0 sound/core/seq/seq_clientmgr.c:613
_snd_seq_deliver_single_event sound/core/seq/seq_clientmgr.c:672 [inline]
snd_seq_deliver_single_event+0x31f/0x8c0 sound/core/seq/seq_clientmgr.c:687
snd_seq_deliver_event+0x44b/0x860 sound/core/seq/seq_clientmgr.c:815
snd_seq_kernel_client_dispatch+0x16f/0x1b0 sound/core/seq/seq_clientmgr.c:2439
send_timer_event.isra.0+0x130/0x190 sound/core/seq/oss/seq_oss_timer.c:140
snd_seq_oss_timer_start+0x1db/0x320 sound/core/seq/oss/seq_oss_timer.c:161
send_midi_event sound/core/seq/oss/seq_oss_midi.c:576 [inline]
snd_seq_oss_midi_input+0x467/0xa30 sound/core/seq/oss/seq_oss_midi.c:501
snd_seq_oss_event_input+0x194/0x250 sound/core/seq/oss/seq_oss_event.c:429
__snd_seq_deliver_single_event sound/core/seq/seq_clientmgr.c:626 [inline]
__snd_seq_deliver_single_event+0x127/0x1c0 sound/core/seq/seq_clientmgr.c:613
_snd_seq_deliver_single_event sound/core/seq/seq_clientmgr.c:672 [inline]
snd_seq_deliver_single_event+0x31f/0x8c0 sound/core/seq/seq_clientmgr.c:687
__deliver_to_subscribers sound/core/seq/seq_clientmgr.c:735 [inline]
deliver_to_subscribers sound/core/seq/seq_clientmgr.c:763 [inline]
snd_seq_deliver_event+0x2c1/0x860 sound/core/seq/seq_clientmgr.c:813
snd_seq_kernel_client_dispatch+0x16f/0x1b0 sound/core/seq/seq_clientmgr.c:2439
snd_midi_input_event+0x32f/0x470 sound/core/seq/seq_midi.c:93
snd_rawmidi_input_event_work+0x61/0x80 sound/core/rawmidi.c:127
process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
process_scheduled_works kernel/workqueue.c:3405 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</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