============================================
WARNING: possible recursive locking detected
4.14.0-rc5-mm1+ #20 Not tainted
--------------------------------------------
syzkaller119895/2984 is trying to acquire lock:
 (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] deliver_to_subscribers sound/core/seq/seq_clientmgr.c:666 [inline]
 (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] snd_seq_deliver_event+0x553/0x820 sound/core/seq/seq_clientmgr.c:811

but task is already holding lock:
 (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] deliver_to_subscribers sound/core/seq/seq_clientmgr.c:666 [inline]
 (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] snd_seq_deliver_event+0x553/0x820 sound/core/seq/seq_clientmgr.c:811

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

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

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syzkaller119895/2984:
 #0:  (register_mutex#4){+.+.}, at: [<ffffffff83e3b8da>] odev_release+0x4a/0x70 sound/core/seq/oss/seq_oss.c:152
 #1:  (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] deliver_to_subscribers sound/core/seq/seq_clientmgr.c:666 [inline]
 #1:  (&grp->list_mutex){++++}, at: [<ffffffff83e28dc3>] snd_seq_deliver_event+0x553/0x820 sound/core/seq/seq_clientmgr.c:811

stack backtrace:
CPU: 0 PID: 2984 Comm: syzkaller119895 Not tainted 4.14.0-rc5-mm1+ #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 print_deadlock_bug kernel/locking/lockdep.c:1796 [inline]
 check_deadlock kernel/locking/lockdep.c:1843 [inline]
 validate_chain kernel/locking/lockdep.c:2444 [inline]
 __lock_acquire+0xed5/0x3d50 kernel/locking/lockdep.c:3487
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3991
 down_read+0x96/0x150 kernel/locking/rwsem.c:23
 deliver_to_subscribers sound/core/seq/seq_clientmgr.c:666 [inline]
 snd_seq_deliver_event+0x553/0x820 sound/core/seq/seq_clientmgr.c:811
 snd_seq_kernel_client_dispatch+0x11e/0x150 sound/core/seq/seq_clientmgr.c:2317
 dummy_input+0x2c4/0x400 sound/core/seq/seq_dummy.c:104
 snd_seq_deliver_single_event.constprop.11+0x2fb/0x940 sound/core/seq/seq_clientmgr.c:621
 deliver_to_subscribers sound/core/seq/seq_clientmgr.c:676 [inline]
 snd_seq_deliver_event+0x362/0x820 sound/core/seq/seq_clientmgr.c:811
 snd_seq_kernel_client_dispatch+0x11e/0x150 sound/core/seq/seq_clientmgr.c:2317
 dummy_input+0x2c4/0x400 sound/core/seq/seq_dummy.c:104
 snd_seq_deliver_single_event.constprop.11+0x2fb/0x940 sound/core/seq/seq_clientmgr.c:621
 snd_seq_deliver_event+0x176/0x820 sound/core/seq/seq_clientmgr.c:822
 snd_seq_kernel_client_dispatch+0x11e/0x150 sound/core/seq/seq_clientmgr.c:2317
 snd_seq_oss_dispatch sound/core/seq/oss/seq_oss_device.h:150 [inline]
 snd_seq_oss_midi_reset+0x44b/0x700 sound/core/seq/oss/seq_oss_midi.c:481
 snd_seq_oss_synth_reset+0x398/0x980 sound/core/seq/oss/seq_oss_synth.c:416
 snd_seq_oss_reset+0x6c/0x260 sound/core/seq/oss/seq_oss_init.c:448
 snd_seq_oss_release+0x71/0x120 sound/core/seq/oss/seq_oss_init.c:425
 odev_release+0x52/0x70 sound/core/seq/oss/seq_oss.c:153
 __fput+0x327/0x7e0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x199/0x270 kernel/task_work.c:112
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0x9b5/0x1ad0 kernel/exit.c:869
 do_group_exit+0x149/0x400 kernel/exit.c:972
 SYSC_exit_group kernel/exit.c:983 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:981
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x442c58