linux-kernel - Re: rcu_prempt stalls / lockup

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Message-ID: <20140401150849.GA14757@redhat.com>
Date:	Tue, 1 Apr 2014 11:08:49 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: rcu_prempt stalls / lockup

On Mon, Mar 31, 2014 at 05:48:01PM -0700, Paul E. McKenney wrote:
 
 > Alternatively, I suppose a wakeup could be getting lost.  The main change
 > related to that this merge window was ffa83fb565fb, which eliminated
 > idle wakeups from RCU in the CONFIG_RCU_NOCB_CPU_ALL=y case.
 > 
 > So, could you please try reverting ffa83fb565fb?

Did a run overnight with that reverted, no luck..

[11869.580161] INFO: rcu_preempt detected stalls on CPUs/tasks:
[11869.581245]  (detected by 0, t=6502 jiffies, g=449892, c=449891, q=0)
[11869.582047] INFO: Stall ended before state dump start
[12064.517461] INFO: rcu_preempt detected stalls on CPUs/tasks:
[12064.518539]  (detected by 0, t=26007 jiffies, g=449892, c=449891, q=0)
[12064.519347] INFO: Stall ended before state dump start
[12259.454767] INFO: rcu_preempt detected stalls on CPUs/tasks:
[12259.455818]  (detected by 0, t=45512 jiffies, g=449892, c=449891, q=0)
[12259.456602] INFO: Stall ended before state dump start
[12454.392112] INFO: rcu_preempt detected stalls on CPUs/tasks:
[12454.393131]  (detected by 0, t=65017 jiffies, g=449892, c=449891, q=0)
[12454.393942] INFO: Stall ended before state dump start
[12649.329446] INFO: rcu_preempt detected stalls on CPUs/tasks:
[12649.330446]  (detected by 0, t=84522 jiffies, g=449892, c=449891, q=0)
[12649.331267] INFO: Stall ended before state dump start
[12844.266776] INFO: rcu_preempt detected stalls on CPUs/tasks:
[12844.267695]  (detected by 0, t=104027 jiffies, g=449892, c=449891, q=0)
[12844.268571] INFO: Stall ended before state dump start
[13039.204102] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13039.205119]  (detected by 0, t=123532 jiffies, g=449892, c=449891, q=0)
[13039.205871] INFO: Stall ended before state dump start
[13234.141424] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13234.141424] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13234.142448]  (detected by 0, t=143037 jiffies, g=449892, c=449891, q=0)
[13234.143339] INFO: Stall ended before state dump start
[13429.078730] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13429.079771]  (detected by 0, t=162542 jiffies, g=449892, c=449891, q=0)
[13429.080591] INFO: Stall ended before state dump start
[13624.016058] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13624.017116]  (detected by 0, t=182047 jiffies, g=449892, c=449891, q=0)
[13624.018033] INFO: Stall ended before state dump start
[13818.953370] INFO: rcu_preempt detected stalls on CPUs/tasks:
[13818.954437]  (detected by 0, t=201552 jiffies, g=449892, c=449891, q=0)
[13818.955334] INFO: Stall ended before state dump start
[14013.890682] INFO: rcu_preempt detected stalls on CPUs/tasks:
[14013.891761]  (detected by 0, t=221057 jiffies, g=449892, c=449891, q=0)
[14013.892691] INFO: Stall ended before state dump start
[14208.827993] INFO: rcu_preempt detected stalls on CPUs/tasks:
[14208.829088]  (detected by 0, t=240562 jiffies, g=449892, c=449891, q=0)
[14208.829977] INFO: Stall ended before state dump start
[14403.765300] INFO: rcu_preempt detected stalls on CPUs/tasks:
[14403.766405]  (detected by 0, t=260067 jiffies, g=449892, c=449891, q=0)
and on and on..

so kernel space still works like before, but userspace is locked up.

 > If that doesn't work, I will need to put together some diagnostic patches.
 > Starting with the one below.

bugger, I forgot to apply this last night. I'll do it on the next run.

	Dave

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