Re: rcu_preempt detected stalls.

[Sasha Levin]

On 10/24/2014 12:13 PM, Paul E. McKenney wrote:
> On Fri, Oct 24, 2014 at 08:28:40AM -0400, Sasha Levin wrote:
>> > On 10/23/2014 03:58 PM, Paul E. McKenney wrote:
>>> > > On Thu, Oct 23, 2014 at 02:55:43PM -0400, Sasha Levin wrote:
>>>>> > >> > On 10/23/2014 02:39 PM, Paul E. McKenney wrote:
>>>>>>> > >>> > > On Tue, Oct 14, 2014 at 10:35:10PM -0400, Sasha Levin wrote:
>>>>>>>>> > >>>> > >> On 10/13/2014 01:35 PM, Dave Jones wrote:
>>>>>>>>>>> > >>>>> > >>> oday in "rcu stall while fuzzing" news:
>>>>>>>>>>> > >>>>> > >>>
>>>>>>>>>>> > >>>>> > >>> INFO: rcu_preempt detected stalls on CPUs/tasks:
>>>>>>>>>>> > >>>>> > >>> 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646
>>>>>>>>>>> > >>>>> > >>> 	Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646
>>>>>>>>>>> > >>>>> > >>> 	(detected by 0, t=6502 jiffies, g=75434, c=75433, q=0)
>>>>>>>>> > >>>> > >>
>>>>>>>>> > >>>> > >> I've complained about RCU stalls couple days ago (in a different context)
>>>>>>>>> > >>>> > >> on -next. I guess whatever causing them made it into Linus's tree?
>>>>>>>>> > >>>> > >>
>>>>>>>>> > >>>> > >> https://lkml.org/lkml/2014/10/11/64
>>>>>>> > >>> > > 
>>>>>>> > >>> > > And on that one, I must confess that I don't see where the RCU read-side
>>>>>>> > >>> > > critical section might be.
>>>>>>> > >>> > > 
>>>>>>> > >>> > > Hmmm...  Maybe someone forgot to put an rcu_read_unlock() somewhere.
>>>>>>> > >>> > > Can you reproduce this with CONFIG_PROVE_RCU=y?
>>>>> > >> > 
>>>>> > >> > Paul, if that was directed to me - Yes, I see stalls with CONFIG_PROVE_RCU
>>>>> > >> > set and nothing else is showing up before/after that.
>>> > > Indeed it was directed to you.  ;-)
>>> > > 
>>> > > Does the following crude diagnostic patch turn up anything?
>> > 
>> > Nope, seeing stalls but not seeing that pr_err() you added.
> OK, color me confused.  Could you please send me the full dmesg or a
> pointer to it?

Attached.


Thanks,
Sasha

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