linux-kernel - Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

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Message-ID: <20160325214623.GR4287@linux.vnet.ibm.com>
Date:	Fri, 25 Mar 2016 14:46:23 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Chatre, Reinette" <reinette.chatre@...el.com>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Josh Triplett <josh@...htriplett.org>,
	Ross Green <rgkernel@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	"dipankar@...ibm.com" <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	pranith kumar <bobby.prani@...il.com>
Subject: Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

On Fri, Mar 25, 2016 at 09:24:14PM +0000, Chatre, Reinette wrote:
> Hi  Paul,
> 
> On 2016-03-23, Paul E. McKenney wrote:
> > Please boot with the following parameters:
> > 
> > 	rcu_tree.rcu_kick_kthreads ftrace
> > trace_event=sched_waking,sched_wakeup,sched_wake_idle_without_ipi
> 
> With these parameters I expected more details to show up in the kernel logs but cannot find any. Even so, today I left the machine running again and when this happened I think I was able to capture the trace data for the event. Please find attached the trace information for the kernel message below. Since the complete trace file is very big I trimmed it to show the time around this event - hopefully this will contain the information you need. I would also like to provide some additional information. The system on which I see these events had a time that was _very_ wrong. I noticed that this issue occurs when system-timesynd was one of the tasks calling the functions of interest to your tracing and am wondering if a very out of sync time in process of being corrected could be the cause of this issue? As an experiment I ensured the system time was accurate before leaving the system idle overnight and I did not see the issue the next morning. 

Ah!  Yes, a sudden jump in time or a disagreement about the time among
different components of the system can definitely cause these symptoms.
We have sometimes seen these problems occur when a pair of CPUs have
wildly different ideas about what time it is, for example.  Please let
me know how it goes.

Also, in your trace, there are no sched_waking events for the rcu_preempt
process that are not immediately followed by sched_wakeup, so your trace
isn't showing the problem that I am seeing.

Still beating up on my stress test, which is not yet proving to be all
that stressful.  :-/

							Thanx, Paul

> [  957.396537] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [  957.399933]  1-...: (0 ticks this GP) idle=4d6/0/0 softirq=6311/6311 fqs=0
> [  957.403661]  (detected by 0, t=60002 jiffies, g=3583, c=3582, q=47)
> [  957.407227] Task dump for CPU 1:
> [  957.409964] swapper/1       R  running task        0     0      1 0x00200000
> [  957.413770]  0000039daa9a7eb9 ffff8801785cfed0 ffffffff818af34c ffff880100000000
> [  957.417696]  0000000600000003 ffff8801785d0000 ffff880072f9ea00 ffffffff822dcf80
> [  957.421631]  ffff8801785cc000 ffff8801785cc000 ffff8801785cfee0 ffffffff818af597
> [  957.425562] Call Trace:
> [  957.428124]  [<ffffffff818af34c>] ? cpuidle_enter_state+0xfc/0x310
> [  957.431713]  [<ffffffff818af597>] ? cpuidle_enter+0x17/0x20
> [  957.435122]  [<ffffffff811515ba>] ? call_cpuidle+0x2a/0x40
> [  957.438467]  [<ffffffff8115198d>] ? cpu_startup_entry+0x28d/0x360
> [  957.441949]  [<ffffffff8108c864>] ? start_secondary+0x114/0x140
> [  957.445378] rcu_preempt kthread starved for 60002 jiffies! g3583 c3582 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1
> [  957.449834] rcu_preempt     S ffff8801785b7d68     0     7      2 0x00000000
> [  957.453579]  ffff8801785b7d68 ffff88017dc8cc80 ffff88016fe6bb80 ffff8801785abb80
> [  957.457428]  ffff8801785b8000 ffff8801785b7da0 ffff88017dc8cc80 ffff88017dc8cc80
> [  957.461249]  0000000000000003 ffff8801785b7d80 ffffffff81ab03df 0000000100373021
> [  957.465055] Call Trace:
> [  957.467493]  [<ffffffff81ab03df>] schedule+0x3f/0xa0
> [  957.470613]  [<ffffffff81ab4397>] schedule_timeout+0x127/0x270
> [  957.473976]  [<ffffffff81171a00>] ? detach_if_pending+0x120/0x120
> [  957.477387]  [<ffffffff8116d983>] rcu_gp_kthread+0x6d3/0xa40
> [  957.480659]  [<ffffffff811513a0>] ? wake_atomic_t_function+0x70/0x70
> [  957.484123]  [<ffffffff8116d2b0>] ? force_qs_rnp+0x1b0/0x1b0
> [  957.487392]  [<ffffffff8112f856>] kthread+0xe6/0x100
> [  957.490470]  [<ffffffff8112f770>] ? kthread_worker_fn+0x190/0x190
> [  957.493859]  [<ffffffff81ab5ccf>] ret_from_fork+0x3f/0x70
> [  957.497044]  [<ffffffff8112f770>] ? kthread_worker_fn+0x190/0x190
> 
> Reinette