Re: RCU stalls when running out of memory on 3.14-rc4 w/ NFS and kernel threads priorities changed

[Eric Dumazet]

On Tue, 2014-03-04 at 15:55 -0800, Florian Fainelli wrote:
> Hi all,
> 
> I am seeing the following RCU stalls messages appearing on an ARMv7
> 4xCPUs system running 3.14-rc4:
> 
> [   42.974327] INFO: rcu_sched detected stalls on CPUs/tasks:
> [   42.979839]  (detected by 0, t=2102 jiffies, g=4294967082,
> c=4294967081, q=516)
> [   42.987169] INFO: Stall ended before state dump start
> 
> this is happening under the following conditions:
> 
> - the attached bumper.c binary alters various kernel thread priorities
> based on the contents of bumpup.cfg and
> - malloc_crazy is running from a NFS share
> - malloc_crazy.c is running in a loop allocating chunks of memory but
> never freeing it
> 
> when the priorities are altered, instead of getting the OOM killer to
> be invoked, the RCU stalls are happening. Taking NFS out of the
> equation does not allow me to reproduce the problem even with the
> priorities altered.
> 
> This "problem" seems to have been there for quite a while now since I
> was able to get 3.8.13 to trigger that bug as well, with a slightly
> more detailed RCU debugging trace which points the finger at kswapd0.
> 
> You should be able to get that reproduced under QEMU with the
> Versatile Express platform emulating a Cortex A15 CPU and the attached
> files.
> 
> Any help or suggestions would be greatly appreciated. Thanks!

Do you have a more complete trace, including stack traces ?




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