syzbot

INFO: rcu_sched self-detected stall on CPU
	0-....: (124999 ticks this GP) idle=a5a/140000000000001/0 softirq=19693/19701 fqs=31184 
	 (t=125000 jiffies g=9342 c=9341 q=8)
NMI backtrace for cpu 0
CPU: 0 PID: 7191 Comm: syz-executor5 Not tainted 4.15.0-rc6+ #248
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x122/0x180 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
 rcu_dump_cpu_stacks+0x186/0x1d9 kernel/rcu/tree.c:1459
 print_cpu_stall kernel/rcu/tree.c:1608 [inline]
 check_cpu_stall.isra.61+0xbb8/0x15b0 kernel/rcu/tree.c:1676
 __rcu_pending kernel/rcu/tree.c:3440 [inline]
 rcu_pending kernel/rcu/tree.c:3502 [inline]
 rcu_check_callbacks+0x256/0xd00 kernel/rcu/tree.c:2842
 update_process_times+0x30/0x60 kernel/time/timer.c:1628
 tick_sched_handle+0x85/0x160 kernel/time/tick-sched.c:162
 tick_sched_timer+0x42/0x120 kernel/time/tick-sched.c:1194
 __run_hrtimer kernel/time/hrtimer.c:1211 [inline]
 __hrtimer_run_queues+0x358/0xe20 kernel/time/hrtimer.c:1275
 hrtimer_interrupt+0x1c2/0x5e0 kernel/time/hrtimer.c:1309
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x14a/0x700 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:920
 </IRQ>
RIP: 0010:mulaw_decode+0x537/0x770 sound/core/oss/mulaw.c:193
RSP: 0018:ffff8801d50278b0 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff11
RAX: ffffc900012579d2 RBX: ffffc90001259ce9 RCX: 0000000000000000
RDX: 0000000000000002 RSI: ffff8801d5027972 RDI: ffffc900012579d4
RBP: ffff8801d50279d8 R08: fffff5200024af3b R09: fffff5200024af3b
R10: 0000000000000001 R11: fffff5200024af3a R12: 0000000000000002
R13: ffff8801d5e0e100 R14: dffffc0000000000 R15: ffffc900012579d2
 mulaw_transfer+0x222/0x270 sound/core/oss/mulaw.c:273
 snd_pcm_plug_write_transfer+0x22d/0x420 sound/core/oss/pcm_plugin.c:611
 snd_pcm_oss_write2+0x260/0x420 sound/core/oss/pcm_oss.c:1311
 snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1372 [inline]
 snd_pcm_oss_write+0x5fe/0x830 sound/core/oss/pcm_oss.c:2646
 __vfs_write+0xef/0x970 fs/read_write.c:480
 vfs_write+0x189/0x510 fs/read_write.c:544
 SYSC_write fs/read_write.c:589 [inline]
 SyS_write+0xef/0x220 fs/read_write.c:581
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007f39cbddbc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
RDX: 00000000fffffec0 RSI: 00000000205c7000 RDI: 0000000000000014
RBP: 00000000000003fa R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4010
R13: 00000000ffffffff R14: 00007f39cbddc6d4 R15: 0000000000000000