Hello,

syzbot found the following issue on:

HEAD commit: cf6c9d12750c Add linux-next specific files for 20211022 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=15d3d4c4b00000 kernel config: https://syzkaller.appspot.com/x/.config?x=e694204255ade3a3 dashboard link: https://syzkaller.appspot.com/bug?extid=ace149a75a9a0a399ac7 compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17c0530cb00000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1129c952b00000

The issue was bisected to:

commit 411cef6adfb38a5bb6bd9af3941b28198e7fb680 Author: Takashi Iwai tiwai@suse.de Date: Wed Oct 20 16:48:46 2021 +0000

ALSA: mixer: oss: Fix racy access to slots

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=167f6454b00000 final oops: https://syzkaller.appspot.com/x/report.txt?x=157f6454b00000 console output: https://syzkaller.appspot.com/x/log.txt?x=117f6454b00000

IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+ace149a75a9a0a399ac7@syzkaller.appspotmail.com Fixes: 411cef6adfb3 ("ALSA: mixer: oss: Fix racy access to slots")

============================================ WARNING: possible recursive locking detected 5.15.0-rc6-next-20211022-syzkaller #0 Not tainted -------------------------------------------- syz-executor206/6529 is trying to acquire lock: ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_set_volume sound/core/oss/mixer_oss.c:316 [inline] ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_ioctl1+0x630/0x19a0 sound/core/oss/mixer_oss.c:375

but task is already holding lock: ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_set_volume sound/core/oss/mixer_oss.c:300 [inline] ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_ioctl1+0x4b1/0x19a0 sound/core/oss/mixer_oss.c:375

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

CPU0 ---- lock(&mixer->reg_mutex); lock(&mixer->reg_mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by syz-executor206/6529: #0: ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_set_volume sound/core/oss/mixer_oss.c:300 [inline] #0: ffff888021ff09c8 (&mixer->reg_mutex){+.+.}-{3:3}, at: snd_mixer_oss_ioctl1+0x4b1/0x19a0 sound/core/oss/mixer_oss.c:375

stack backtrace: CPU: 0 PID: 6529 Comm: syz-executor206 Not tainted 5.15.0-rc6-next-20211022-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline] check_deadlock kernel/locking/lockdep.c:2999 [inline] validate_chain kernel/locking/lockdep.c:3788 [inline] __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5027 lock_acquire kernel/locking/lockdep.c:5637 [inline] lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5602 __mutex_lock_common kernel/locking/mutex.c:607 [inline] __mutex_lock+0x12f/0x12f0 kernel/locking/mutex.c:740 snd_mixer_oss_set_volume sound/core/oss/mixer_oss.c:316 [inline] snd_mixer_oss_ioctl1+0x630/0x19a0 sound/core/oss/mixer_oss.c:375 snd_mixer_oss_ioctl+0x40/0x50 sound/core/oss/mixer_oss.c:390 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl fs/ioctl.c:860 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f0c06979fe9 Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffea97dd558 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0c06979fe9 RDX: 0000000020000080 RSI: 00000000c0044d00 RDI: 0000000000000003 RBP: 00007f0c0693dfd0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0c0693e060 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 </TASK>

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