Kernel bug: possible deadlock in __snd_pcm_lib_xfer (2)
Subsystem: sound
Status: fixed

Crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.48/6160 is trying to acquire lock:
ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
ffff8880b8923d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168

but task is already holding lock:
ffff88802f930150 (&group->lock#2){+.+.}-{3:3}, at: __snd_pcm_lib_xfer+0x386/0x1ce0 sound/core/pcm_lib.c:2319

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+0x22c/0x710 kernel/softirq.c:579
       __do_softirq kernel/softirq.c:613 [inline]
       run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
       smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
       kthread+0x711/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x3fc/0x770 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+0x22c/0x710 kernel/softirq.c:579
       __do_softirq kernel/softirq.c:613 [inline]
       run_ktimerd+0xcf/0x190 kernel/softirq.c:1043
       smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
       kthread+0x711/0x8a0 kernel/kthread.c:463
       ret_from_fork+0x3fc/0x770 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+0x12a/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_xrun+0x27f/0x7c0 sound/core/pcm_lib.c:180
       snd_pcm_update_state+0x342/0x430 sound/core/pcm_lib.c:224
       snd_pcm_update_hw_ptr0+0x10b2/0x1b00 sound/core/pcm_lib.c:493
       snd_pcm_update_hw_ptr sound/core/pcm_lib.c:499 [inline]
       __snd_pcm_lib_xfer+0x510/0x1ce0 sound/core/pcm_lib.c:2326
       snd_pcm_oss_write3+0x1bc/0x320 sound/core/oss/pcm_oss.c:1241
       snd_pcm_plug_write_transfer+0x2cb/0x4c0 sound/core/oss/pcm_plugin.c:630
       snd_pcm_oss_write2 sound/core/oss/pcm_oss.c:1373 [inline]
       snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1439 [inline]
       snd_pcm_oss_write+0xba2/0x11a0 sound/core/oss/pcm_oss.c:2795
       vfs_write+0x284/0xb40 fs/read_write.c:684
       ksys_write+0x14b/0x260 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       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.0.48/6160:
 #0: ffff88802f930150 (&group->lock#2){+.+.}-{3:3}, at: __snd_pcm_lib_xfer+0x386/0x1ce0 sound/core/pcm_lib.c:2319
 #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
 #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57

stack backtrace:
CPU: 1 UID: 0 PID: 6160 Comm: syz.0.48 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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+0x12a/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_xrun+0x27f/0x7c0 sound/core/pcm_lib.c:180
 snd_pcm_update_state+0x342/0x430 sound/core/pcm_lib.c:224
 snd_pcm_update_hw_ptr0+0x10b2/0x1b00 sound/core/pcm_lib.c:493
 snd_pcm_update_hw_ptr sound/core/pcm_lib.c:499 [inline]
 __snd_pcm_lib_xfer+0x510/0x1ce0 sound/core/pcm_lib.c:2326
 snd_pcm_oss_write3+0x1bc/0x320 sound/core/oss/pcm_oss.c:1241
 snd_pcm_plug_write_transfer+0x2cb/0x4c0 sound/core/oss/pcm_plugin.c:630
 snd_pcm_oss_write2 sound/core/oss/pcm_oss.c:1373 [inline]
 snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1439 [inline]
 snd_pcm_oss_write+0xba2/0x11a0 sound/core/oss/pcm_oss.c:2795
 vfs_write+0x284/0xb40 fs/read_write.c:684
 ksys_write+0x14b/0x260 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0e7a70ebe9
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:00007ffe73a3cd48 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f0e7a935fa0 RCX: 00007f0e7a70ebe9
RDX: 000000000000fc36 RSI: 0000200000000500 RDI: 0000000000000003
RBP: 00007f0e7a791e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0e7a935fa0 R14: 00007f0e7a935fa0 R15: 0000000000000003
 </TASK>