Re: INFO: rcu detected stall in memcpy

[Takashi Iwai]

On Thu, 04 Jan 2018 13:08:45 +0100,
Dmitry Vyukov wrote:
> 
> On Thu, Jan 4, 2018 at 1:03 PM, syzbot
> <syzbot+387f48da65cb522abfe8@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > Hello,
> >
> > syzkaller hit the following crash on
> > 30a7acd573899fd8b8ac39236eff6468b195ac7d
> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.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.
> >
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+387f48da65cb522abfe8@xxxxxxxxxxxxxxxxxxxxxxxxx
> > It will help syzbot understand when the bug is fixed. See footer for
> > details.
> > If you forward the report, please keep this part and the footer.
> 
> This looks ALSA-related. +ALSA maintainers.

Not sure exactly what triggers it.  It's the simple memcpy(), and I
don't know where RCU is involved in that code path.

BTW, other two suspicious RCU usage reports are actually stopped at
the second WARN_ON() after the RCU message, and the second WARN_ON()
is independent from RCU; it's the known spurious WARN_ON() and was
already removed in the sound git tree.


thanks,

Takashi

> > INFO: rcu_sched detected stalls on CPUs/tasks:
> >         (detected by 0, t=125002 jiffies, g=15654, c=15653, q=133)
> > All QSes seen, last rcu_sched kthread activity 125002
> > (4294863411-4294738409), jiffies_till_next_fqs=3, root ->qsmask 0x0
> > syz-executor1   R  running task    24936 11943   3739 0x0000000c
> > Call Trace:
> >  <IRQ>
> >  sched_show_task+0x4a3/0x5e0 kernel/sched/core.c:5198
> >  print_other_cpu_stall+0x996/0x1090 kernel/rcu/tree.c:1564
> >  check_cpu_stall.isra.61+0x6e6/0x15b0 kernel/rcu/tree.c:1682
> >  __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:kasan_mem_to_shadow include/linux/kasan.h:30 [inline]
> > RIP: 0010:memory_is_poisoned_n mm/kasan/kasan.c:210 [inline]
> > RIP: 0010:memory_is_poisoned mm/kasan/kasan.c:241 [inline]
> > RIP: 0010:check_memory_region_inline mm/kasan/kasan.c:257 [inline]
> > RIP: 0010:check_memory_region+0x38/0x190 mm/kasan/kasan.c:267
> > RSP: 0000:ffff8801bd2ff868 EFLAGS: 00000212 ORIG_RAX: ffffffffffffff11
> > RAX: ffff7fffffffffff RBX: ffffc9000160020b RCX: ffffffff841fceaf
> > RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffffc9000160020a
> > RBP: ffff8801bd2ff878 R08: ffffc9000160020a R09: dffffc0000000000
> > R10: 0000000000000001 R11: ffffed0037a5ff2e R12: ffffc9000160020a
> > R13: ffff8801bd2ff970 R14: dffffc0000000000 R15: ffffc9000160020a
> >  memcpy+0x37/0x50 mm/kasan/kasan.c:303
> >  memcpy include/linux/string.h:344 [inline]
> >  cvt_s16_to_native sound/core/oss/mulaw.c:164 [inline]
> >  mulaw_decode+0x52f/0x770 sound/core/oss/mulaw.c:195
> >  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:00007fa354a13c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: cccccccccccccccd RCX: 0000000000452ac9
> > RDX: 00000000fffffeb2 RSI: 0000000020083fc6 RDI: 0000000000000014
> > RBP: 00000000000005b5 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f6998
> > R13: 00000000ffffffff R14: 00007fa354a146d4 R15: 0000000000000000
> > rcu_sched kthread starved for 125002 jiffies! g15654 c15653 f0x2
> > RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0
> > rcu_sched       R  running task    23456     8      2 0x80000000
> > Call Trace:
> >  context_switch kernel/sched/core.c:2799 [inline]
> >  __schedule+0x8eb/0x2060 kernel/sched/core.c:3375
> >  schedule+0xf5/0x430 kernel/sched/core.c:3434
> >  schedule_timeout+0x118/0x230 kernel/time/timer.c:1793
> >  rcu_gp_kthread+0x9e5/0x1930 kernel/rcu/tree.c:2314
> >  kthread+0x33c/0x400 kernel/kthread.c:238
> >  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> >
> >
> > ---
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> > See https://goo.gl/tpsmEJ for details.
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