Message-ID: <68dadf0e.050a0220.1696c6.001c.GAE@google.com>
Date: Mon, 29 Sep 2025 12:33:34 -0700
From: syzbot <syzbot+c9ab1eb0f8f5ab1f18be@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org, perex@...ex.cz, 
	syzkaller-bugs@...glegroups.com, tiwai@...e.com
Subject: [syzbot] [sound?] possible deadlock in snd_pcm_drop

Hello,

syzbot found the following issue on:

HEAD commit:    4ff71af020ae Merge tag 'net-6.17-rc8' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1191c2e2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f5b21423ca3f0a96
dashboard link: https://syzkaller.appspot.com/bug?extid=c9ab1eb0f8f5ab1f18be
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1644dd34580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=156d6f12580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3fb4198b5763/disk-4ff71af0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1499875eb2cc/vmlinux-4ff71af0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/182864fb8af7/bzImage-4ff71af0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c9ab1eb0f8f5ab1f18be@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.2869/8991 is trying to acquire lock:
ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168

but task is already holding lock:
ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: spin_lock_irq include/linux/spinlock_rt.h:93 [inline]
ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_group_lock_irq sound/core/pcm_native.c:98 [inline]
ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_stream_lock_irq sound/core/pcm_native.c:137 [inline]
ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: class_pcm_stream_lock_irq_constructor include/sound/pcm.h:679 [inline]
ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_drop+0x10d/0x270 sound/core/pcm_native.c:2223

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&group->lock#2){+.+.}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56
       spin_lock include/linux/spinlock_rt.h:44 [inline]
       _snd_pcm_stream_lock_irqsave+0x7c/0xa0 sound/core/pcm_native.c:171
       class_pcm_stream_lock_irqsave_constructor include/sound/pcm.h:682 [inline]
       snd_pcm_period_elapsed+0x1e/0x80 sound/core/pcm_lib.c:1938
       dummy_hrtimer_callback+0x80/0x180 sound/drivers/dummy.c:386
       __run_hrtimer kernel/time/hrtimer.c:1761 [inline]
       __hrtimer_run_queues+0x54f/0xd40 kernel/time/hrtimer.c:1825
       hrtimer_run_softirq+0x1a3/0x2e0 kernel/time/hrtimer.c:1842
       handle_softirqs+0x22f/0x710 kernel/softirq.c:579
       __do_softirq kernel/softirq.c:613 [inline]
       run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
       smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160
       kthread+0x70e/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (&base->softirq_expiry_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56
       spin_lock include/linux/spinlock_rt.h:44 [inline]
       hrtimer_cpu_base_lock_expiry kernel/time/hrtimer.c:1383 [inline]
       hrtimer_run_softirq+0x7c/0x2e0 kernel/time/hrtimer.c:1838
       handle_softirqs+0x22f/0x710 kernel/softirq.c:579
       __do_softirq kernel/softirq.c:613 [inline]
       run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
       smpboot_thread_fn+0x53f/0xa60 kernel/smpboot.c:160
       kthread+0x70e/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 ((softirq_ctrl.lock)){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
       __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
       hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491
       dummy_hrtimer_stop+0xcf/0x100 sound/drivers/dummy.c:410
       snd_pcm_do_stop+0x127/0x1c0 sound/core/pcm_native.c:1525
       snd_pcm_action_single sound/core/pcm_native.c:1305 [inline]
       snd_pcm_action+0xe4/0x240 sound/core/pcm_native.c:1388
       snd_pcm_stop sound/core/pcm_native.c:1561 [inline]
       snd_pcm_drop+0x160/0x270 sound/core/pcm_native.c:2228
       snd_pcm_oss_sync+0x1de/0xc30 sound/core/oss/pcm_oss.c:1733
       snd_pcm_oss_release+0x102/0x250 sound/core/oss/pcm_oss.c:2574
       __fput+0x45b/0xa80 fs/file_table.c:468
       task_work_run+0x1d4/0x260 kernel/task_work.c:227
       resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
       exit_to_user_mode_loop+0xec/0x110 kernel/entry/common.c:43
       exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
       syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
       syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
       do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  (softirq_ctrl.lock) --> &base->softirq_expiry_lock --> &group->lock#2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&group->lock#2);
                               lock(&base->softirq_expiry_lock);
                               lock(&group->lock#2);
  lock((softirq_ctrl.lock));

 *** DEADLOCK ***

2 locks held by syz.2.2869/8991:
 #0: ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: spin_lock_irq include/linux/spinlock_rt.h:93 [inline]
 #0: ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_group_lock_irq sound/core/pcm_native.c:98 [inline]
 #0: ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_stream_lock_irq sound/core/pcm_native.c:137 [inline]
 #0: ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: class_pcm_stream_lock_irq_constructor include/sound/pcm.h:679 [inline]
 #0: ffff8880302d0150 (&group->lock#2){+.+.}-{3:3}, at: snd_pcm_drop+0x10d/0x270 sound/core/pcm_native.c:2223
 #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
 #1: ffffffff8d9a8d80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57

stack backtrace:
CPU: 0 UID: 0 PID: 8991 Comm: syz.2.2869 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
 __lock_release kernel/locking/lockdep.c:5574 [inline]
 lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
 __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
 hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491
 dummy_hrtimer_stop+0xcf/0x100 sound/drivers/dummy.c:410
 snd_pcm_do_stop+0x127/0x1c0 sound/core/pcm_native.c:1525
 snd_pcm_action_single sound/core/pcm_native.c:1305 [inline]
 snd_pcm_action+0xe4/0x240 sound/core/pcm_native.c:1388
 snd_pcm_stop sound/core/pcm_native.c:1561 [inline]
 snd_pcm_drop+0x160/0x270 sound/core/pcm_native.c:2228
 snd_pcm_oss_sync+0x1de/0xc30 sound/core/oss/pcm_oss.c:1733
 snd_pcm_oss_release+0x102/0x250 sound/core/oss/pcm_oss.c:2574
 __fput+0x45b/0xa80 fs/file_table.c:468
 task_work_run+0x1d4/0x260 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xec/0x110 kernel/entry/common.c:43
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc9f7ffeec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffef674cdc8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 0000000000036070 RCX: 00007fc9f7ffeec9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000bf674d0bf
R10: 0000001b31c20000 R11: 0000000000000246 R12: 00007fc9f8255fac
R13: 00007fc9f8255fa0 R14: ffffffffffffffff R15: 0000000000000003
 </TASK>


---
This report is generated by a bot. It may contain errors.
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