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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 4 Mar 2020 09:33:50 +0100
Message-ID: <CACT4Y+ZqVOHSa+xrOXF+cOwuB_1_q-6+Z5A2SqKw_D1hT2mbQQ@mail.gmail.com>
Subject: Re: INFO: rcu detected stall in sys_keyctl
To:     Kris Karas <linux-1993@moonlit-rail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>
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On Wed, Mar 4, 2020 at 9:32 AM Kris Karas <linux-1993@moonlit-rail.com> wrote:
>
> Dmitry Vyukov wrote:
> > syzbot wrote:
> >> Call Trace:
> >>   <IRQ>
> >>   __dump_stack lib/dump_stack.c:77 [inline]
> >>   dump_stack+0x197/0x210 lib/dump_stack.c:118
> >>   nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
> >>   nmi_trigger_cpumask_backtrace+0x23b/0x28b 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:164 [inline]
> >>   rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree_stall.h:254
> >>   print_cpu_stall kernel/rcu/tree_stall.h:475 [inline]
> >>   check_cpu_stall kernel/rcu/tree_stall.h:549 [inline]
> >>   rcu_pending kernel/rcu/tree.c:3030 [inline]
> >>   rcu_sched_clock_irq.cold+0x51a/0xc37 kernel/rcu/tree.c:2276
> >>   update_process_times+0x2d/0x70 kernel/time/timer.c:1726
> >>   tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:171
> >>   tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1314
> >>   __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
> >>   __hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1579
> >>   hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1641
> >>   local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1119 [inline]
> >>   smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1144
> >>   apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
> >>   </IRQ>
> >>
> > +lib/mpi maintainers
> >
> > I wonder if this can also be triggered by remote actors (tls, wifi, usb, etc).
> >
>
> This looks somewhat similar to an OOPS + rcu stall I reported earlier in
> reply to Greg KH's announcement of 5.5.7:
>
>         rcu: INFO: rcu_sched self-detected stall on CPU
>         rcu:    14-....: (20999 ticks this GP) idle=216/1/0x4000000000000002 softirq=454/454 fqs=5250
>                 (t=21004 jiffies g=-755 q=1327)
>         NMI backtrace for cpu 14
>         CPU: 14 PID: 520 Comm: pidof Tainted: G      D           5.5.7 #1
>         Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./X470 Taichi, BIOS P3.50 07/18/2019
>         Call Trace:
>          <IRQ>
>          dump_stack+0x50/0x70
>          nmi_cpu_backtrace.cold+0x14/0x53
>          ? lapic_can_unplug_cpu.cold+0x44/0x44
>          nmi_trigger_cpumask_backtrace+0x7b/0x88
>          rcu_dump_cpu_stacks+0x7b/0xa9
>          rcu_sched_clock_irq.cold+0x152/0x39b
>          update_process_times+0x1f/0x50
>          tick_sched_timer+0x40/0x90
>          ? tick_sched_do_timer+0x50/0x50
>          __hrtimer_run_queues+0xdd/0x180
>          hrtimer_interrupt+0x108/0x230
>          smp_apic_timer_interrupt+0x53/0xa0
>          apic_timer_interrupt+0xf/0x20
>          </IRQ>
>
> I don't have a reproducer for it, either.  It showed up in 5.5.7 (but
> might be from earlier as it reproduces so infrequently).
>
> Kris

Hi Kris,

Please re-send this to full To/Cc list. Nobody reads LKML/syzbot per se.