INFO: rcu detected stall in mulaw_decode

[syzbot]

Hello,

syzkaller hit the following crash on
ad036b63ee57df9ab802a4eb20cbbbec66aa4520
git://git.cmpxchg.org/linux-mmots.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
Unfortunately, I don't have any reproducer for this bug yet.


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Reported-by: syzbot+ebf0a2...@syzkaller.appspotmail.com
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INFO: rcu_sched self-detected stall on CPU
1-....: (124999 ticks this GP) idle=71e/1/4611686018427387906
softirq=9229/9229 fqs=31218
(t=125000 jiffies g=4571 c=4570 q=876)
NMI backtrace for cpu 1
CPU: 1 PID: 4500 Comm: syz-executor6 Not tainted 4.15.0-rc6-mm1+ #50
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+0x137/0x198 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+0x186/0x1d7 kernel/rcu/tree.c:1375
print_cpu_stall kernel/rcu/tree.c:1524 [inline]
check_cpu_stall kernel/rcu/tree.c:1592 [inline]
__rcu_pending kernel/rcu/tree.c:3362 [inline]
rcu_pending kernel/rcu/tree.c:3424 [inline]
rcu_check_callbacks+0x1a64/0x1de0 kernel/rcu/tree.c:2764
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:1176
__run_hrtimer kernel/time/hrtimer.c:1210 [inline]
__hrtimer_run_queues+0x2c8/0xb50 kernel/time/hrtimer.c:1274
hrtimer_interrupt+0x1c2/0x5e0 kernel/time/hrtimer.c:1308
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
smp_apic_timer_interrupt+0xc9/0x4c0 arch/x86/kernel/apic/apic.c:1050
apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:920
</IRQ>
RIP: 0010:__memcpy+0x0/0x20
RSP: 0018:ffff8801cd597918 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff11
RAX: fffff52000255558 RBX: 0000000000000002 RCX: ffffffff83b7d25e
RDX: 0000000000000002 RSI: ffff8801cd597a00 RDI: ffffc900012aaab8
RBP: ffff8801cd597938 R08: fffff52000255558 R09: fffff52000255558
R10: 0000000000000001 R11: fffff52000255557 R12: ffffc900012aaab8
R13: ffff8801cd597a00 R14: ffff8801d0e45000 R15: dffffc0000000000
memcpy include/linux/string.h:344 [inline]
cvt_s16_to_native sound/core/oss/mulaw.c:164 [inline]
mulaw_decode+0x50e/0x740 sound/core/oss/mulaw.c:195
mulaw_transfer+0x222/0x270 sound/core/oss/mulaw.c:273
snd_pcm_plug_write_transfer+0x20b/0x390 sound/core/oss/pcm_plugin.c:611
snd_pcm_oss_write2+0x22e/0x3c0 sound/core/oss/pcm_oss.c:1311
snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1372 [inline]
snd_pcm_oss_write+0x4c1/0x690 sound/core/oss/pcm_oss.c:2646
__vfs_write+0xef/0x740 fs/read_write.c:480
vfs_write+0x189/0x510 fs/read_write.c:544
SYSC_write fs/read_write.c:589 [inline]
SyS_write+0xd4/0x1a0 fs/read_write.c:581
entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007febc940bc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452ac9
RDX: 00000000ffffffa2 RSI: 0000000020001000 RDI: 0000000000000013
RBP: 0000000000000521 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f5bb8
R13: 00000000ffffffff R14: 00007febc940c6d4 R15: 000000000000000b


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[Dmitry Vyukov]

+ALSA maintainers

This looks like:

#syz dup: INFO: rcu detected stall in memcpy

right?

> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzk...@googlegroups.com.
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
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[Takashi Iwai]

Yes, very likely. And I found that this is a different issue from the
recently fixed aloop bug. It's been already nailed down, and I'll
submit / merge the fixes soon. Hopefully they'll be included in
4.15-rc8.


thanks,

Takashi