If we have a lot of cell object, this cycle may take a long time, and trigger RCU stall. insert a conditional reschedule point to fix it.

rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 1-....: (1 GPs behind) idle=9f5/1/0x4000000000000000 softirq=16474/16475 fqs=4916 (t=10500 jiffies g=19249 q=192515) NMI backtrace for cpu 1 ...... asm_sysvec_apic_timer_interrupt RIP: 0010:_raw_spin_unlock_irqrestore+0x38/0x70 spin_unlock_irqrestore snd_seq_prioq_cell_out+0x1dc/0x360 snd_seq_check_queue+0x1a6/0x3f0 snd_seq_enqueue_event+0x1ed/0x3e0 snd_seq_client_enqueue_event.constprop.0+0x19a/0x3c0 snd_seq_write+0x2db/0x510 vfs_write+0x1c4/0x900 ksys_write+0x171/0x1d0 do_syscall_64+0x35/0xb0

Reported-by: syzbot+bb950e68b400ab4f65f8@syzkaller.appspotmail.com Signed-off-by: Zqiang qiang.zhang1211@gmail.com --- v1->v2: Add atomic context detection.

sound/core/seq/seq_queue.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c index d6c02dea976c..3a05b5e0d555 100644 --- a/sound/core/seq/seq_queue.c +++ b/sound/core/seq/seq_queue.c @@ -263,6 +263,8 @@ void snd_seq_check_queue(struct snd_seq_queue *q, int atomic, int hop) if (!cell) break; snd_seq_dispatch_event(cell, atomic, hop); + if (!atomic) + cond_resched(); }

/* Process time queue... */ @@ -272,6 +274,8 @@ void snd_seq_check_queue(struct snd_seq_queue *q, int atomic, int hop) if (!cell) break; snd_seq_dispatch_event(cell, atomic, hop); + if (!atomic) + cond_resched(); }

/* free lock */