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

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: [email protected]

============================================
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>


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