rcu_sched stall while waiting in csd_lock_wait()

[Peter Zijlstra]

On Thu, Aug 03, 2017 at 09:26:06AM +0530, Pratyush Anand wrote:
> Hi Peter,
> 
> On Wednesday 02 August 2017 01:44 PM, Peter Zijlstra wrote:
> > On Wed, Aug 02, 2017 at 09:01:19AM +0530, Pratyush Anand wrote:
> > > Hi,
> > > 
> > > I am observing following rcu_sched stall while executing `perf record -a  --
> > > sleep 1` with one of the arm64 platform. It looks like that stalled cpu was
> > > waiting in csd_lock_wait() from where it never came out,and so the stall.
> > > Any help/pointer for further debugging would be very helpful. Problem also
> > > reproduced with 4.13.0-rc3.
> > 
> > I'm sitting on this patch:
> > 
> >    https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=locking/core&id=15377ef4fe0c86eb7fa1099575b2e86357d99e42
> > 
> > please give that a spin.
> 
> Thanks for the pointer.

Seems like my brain misfired in any case. That's the OSQ lock not the
CSD one ;-) Let me go stare at your traces with hopefully more
wakefulness.