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Date: Mon, 4 Jan 2016 13:18:38 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Aaron Ma <mapengyu@...il.com>
Cc: linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: RCU stall and the system boot hang with nfsroot
On Mon, Jan 04, 2016 at 06:01:37PM +0800, Aaron Ma wrote:
> On Fri, Jan 1, 2016 at 3:49 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Wed, Dec 30, 2015 at 09:41:45AM -0800, Paul E. McKenney wrote:
> >> On Wed, Dec 30, 2015 at 03:03:33PM +0800, Aaron Ma wrote:
> >> > On Wed, Dec 30, 2015 at 7:42 AM, Paul E. McKenney
> >> > <paulmck@...ux.vnet.ibm.com> wrote:
> >
> > [ . . . ]
> >
> >> > cfg80211: Calling CRDA to update world regulatory domain
> >> > cfg80211: Calling CRDA to update world regulatory domain
> >> > cfg80211: Exceeded CRDA call max attempts. Not calling CRDA
> >> > INFO: rcu_preempt detected stalls on CPUs/tasks:
> >> > 71: (0 ticks this GP) idle=1ac/0/0 softirq=0/0 fqs=0
> >> > (detected by 62, t=26002 jiffies, g=3735, c=3734, q=366014)
> >> > Task dump for CPU 71:
> >> > swapper/71 R running task 0 0 1 0x00200000
> >> > ffffffff81492587 ffff8804633cbe58 ffffffff814f21d7 0000000000000004
> >> > 0000000000000004 ffffe8fffb405310 ffffffff820dc5c0 ffff8804633cbea8
> >> > ffffffff8181db85 0000000000000000 0000000000000000 0000000000000046
> >> > Call Trace:
> >> > [<ffffffff81492587>] ? debug_smp_processor_id+0x17/0x20
> >> > [<ffffffff814f21d7>] ? intel_idle+0x137/0x140
> >> > [<ffffffff8181db85>] ? cpuidle_enter_state+0x65/0x3e0
> >> > [<ffffffff8181df37>] ? cpuidle_enter+0x17/0x20
> >> > [<ffffffff810a849d>] ? cpu_startup_entry+0x33d/0x630
> >> > [<ffffffff8103ceae>] ? start_secondary+0x12e/0x140
> >> > rcu_preempt kthread starved for 26002 jiffies!
> >> > rcu_check_gp_kthread_starvation --->show task:
> >> > rcu_preempt S ffff880456413c68 0 8 2 0x00000000
> >> > ffff880456413c68 ffff8804564025d0 000000000000d7a0 ffff880456b18000
> >> > ffff8804564025d0 ffff880456413c38 ffffffff81492587 ffff880456413c58
> >> > ffff880456414000 ffff8804564025d0 ffff880456413cb8 ffff880869dce500
> >> > Call Trace:
> >> > [<ffffffff81492587>] ? debug_smp_processor_id+0x17/0x20
> >> > [<ffffffff81b5ce9f>] schedule+0x3f/0xd0
> >> > [<ffffffff81b5ef19>] schedule_timeout+0x189/0x3f0
> >> > [<ffffffff810a7904>] ? swait_prepare+0x24/0x90
> >> > [<ffffffff810e8e60>] ? timer_cpu_notify+0x190/0x190
> >> > [<ffffffff810a793b>] ? swait_prepare+0x5b/0x90
> >> > [<ffffffff810de3f8>] rcu_gp_kthread+0x8a8/0x2190
> >> > [<ffffffff810b275d>] ? trace_hardirqs_on+0xd/0x10
> >> > [<ffffffff81b5c18f>] ? __schedule+0x4af/0x1180
> >> > [<ffffffff810ddb50>] ? call_rcu_sched+0x20/0x20
> >> > [<ffffffff8107f844>] kthread+0xe4/0x100
> >> > [<ffffffff810b275d>] ? trace_hardirqs_on+0xd/0x10
> >> > [<ffffffff8107f760>] ? kthread_create_on_node+0x240/0x240
> >> > [<ffffffff81b61562>] ret_from_fork+0x42/0x70
> >> > [<ffffffff8107f760>] ? kthread_create_on_node+0x240/0x240
> >> > rcu_check_gp_kthread_starvation --->end
> >> >
> >> > It seems wait in rcu_gp_kthread. it should be no task blocked right?
> >> > If so, why the swait_event_interruptible_timeout is not awaken? the
> >> > timeout is CONFIG_HZ=1000.
> >>
> >> Given that this happens at boot, perhaps ftrace is a good next step.
> >> The thought would be to enable ftrace via the kernel boot parameters
> >> for the timers.
> >>
> >> And how often does this problem occur?
> >
> > And does the following diagnostic patch help? Its expected behavior
> > would be to turn a hard hang into something that recovered in a few
> > minutes, while giving a few stall-warning splats.
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > commit 7798a5efb2acabfa3ca788dd9b5b118eb1bff443
> > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Date: Thu Dec 31 08:48:36 2015 -0800
> >
> > rcu: Awaken grace-period kthread when stalled
> >
> > Recent kernels can fail to awaken the grace-period kthread for
> > quiescent-state forcing. This commit is a crude hack that does
> > a wakeup any time a stall is detected.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 4b3de6718f7c..51da7ef3561f 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1225,8 +1225,10 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
> > rsp->gp_flags,
> > gp_state_getname(rsp->gp_state), rsp->gp_state,
> > rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
> > - if (rsp->gp_kthread)
> > + if (rsp->gp_kthread) {
> > sched_show_task(rsp->gp_kthread);
> > + wake_up_process(rsp->gp_kthread);
> > + }
> > }
> > }
>
> Sorry for late response because of holiday.
>
> During my knowledge, now this issue is splitted to 2 issues.
>
> First, there is a mistake in the kernel I used.
> I used kernel is changed by someone else, and it ported a patch:
> Author: Thomas Gleixner <tglx@...utronix.de>
> Date: Tue Apr 14 21:08:54 2015 +0000
>
> tick: sched: Force tick interrupt and get rid of softirq magic
>
> commit 0ff53d09642204c648424def0caa9117e7a3caaf upstream
>
> static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
> ktime_t now, int cpu)
> {
> @@ -691,22 +705,18 @@ static ktime_t tick_nohz_stop_sched_tick(struct
> tick_sched *ts,
> if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
> hrtimer_cancel(&ts->sched_timer);
> goto out;
> - }
> + }
>
> - if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
> - hrtimer_start(&ts->sched_timer, expires,
> - HRTIMER_MODE_ABS_PINNED);
> - goto out;
> - } else if (!tick_program_event(expires, 0))
> - goto out;
> - /*
> - * We are past the event already. So we crossed a
> - * jiffie boundary. Update jiffies and raise the
> - * softirq.
> - */
> - tick_do_update_jiffies64(ktime_get());
> + if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
> + hrtimer_start(&ts->sched_timer, expires,
> + HRTIMER_MODE_ABS_PINNED);
> + else
> + tick_program_event(expires, 1);
> + } else {
> + /* Tick is stopped, but required now. Enforce it */
> + tick_nohz_restart(ts, now);
> }
> - raise_softirq_irqoff(TIMER_SOFTIRQ);
> +
>
> It remove the "raise_softirq_irqoff" in tick_nohz_stop_sched_tick, so
> the kernel will be not waked up in idle status.
>
> Second:
> The reason I thought linux-stable-rt has the same issue because of it
> has a boot issue during systemd init:
> mce: [Hardware Error]: PROCESSOR 0:406f0 TIME 1451543174 SOCKET 1 APIC
> 40 microcode 10
> 0000000000000000 ffff880468a0c420 ffff880468a08f58
> Call Trace:
> mce: [Hardware Error]: Run the above through 'mcelog --ascii'
> mce: [Hardware Error]: CPU 22: Machine Check Exception: 0 Bank 20:
> c800008000310e0f
> mce: [Hardware Error]: TSC 0 MISC df87b008d9eff
> mce: [Hardware Error]: PROCESSOR 0:406f0 TIME 1451543174 SOCKET 1 APIC
> 40 microcode 10
> mce: [Hardware Error]: Run the above through 'mcelog --ascii'
> <IRQ> [<ffffffff81b56b53>] dump_stack+0x4a/0x61
> Kernel panic - not syncing: Timeout: Not all CPUs entered broadcast
> exception handler
> [<ffffffff81058a6a>] warn_slowpath_common+0x8a/0xe0
> [<ffffffff81058b7a>] warn_slowpath_null+0x1a/0x20
> [<ffffffff810dafee>] rcu_eqs_exit_common+0x2be/0x550
> [<ffffffff810e32fc>] rcu_irq_enter+0xfc/0x330
> [<ffffffff8105f25e>] irq_enter+0xe/0x60
> [<ffffffff81b63a87>] smp_apic_timer_interrupt+0x37/0x60
> [<ffffffff81b62030>] apic_timer_interrupt+0x70/0x80
> <EOI> <#MC> [<ffffffff81b53b2b>] ? wait_for_panic+0x1a/0x54
> [<ffffffff81b53b31>] ? wait_for_panic+0x20/0x54
> [<ffffffff81b53b2b>] ? wait_for_panic+0x1a/0x54
> [<ffffffff8102f62e>] mce_timed_out+0x7e/0x80
> [<ffffffff81030887>] do_machine_check+0x737/0xa50
> [<ffffffff814f2191>] ? intel_idle+0xd1/0x140
> [<ffffffff81b62e1b>] machine_check+0x2b/0x50
> [<ffffffff814f2191>] ? intel_idle+0xd1/0x140
> <<EOE>> [<ffffffff8181dba5>] cpuidle_enter_state+0x65/0x3e0
> [<ffffffff8181df57>] cpuidle_enter+0x17/0x20
> [<ffffffff810a849d>] cpu_startup_entry+0x33d/0x630
> [<ffffffff8103ceae>] start_secondary+0x12e/0x140
> ---[ end trace 0000000000000002 ]---
>
> I didn't know what's the problem here, so I thought it is caused by
> the same issue.
>
> Now with 1st issue resolved, I am digging the "mce hardware error".
> Do you think this is a hardware issue?
I cannot claim to be an MCE expert. But I am curious. What do you get
when you run the lines through "mcelog --ascii" like it suggests?
Thanx, Paul
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