linux-kernel - Re: rcu_sched stall while waiting in csd_lock

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Date:   Thu, 3 Aug 2017 09:26:24 +0530
From:   Pratyush Anand <panand@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        mark.rutland@....com
Subject: Re: rcu_sched stall while waiting in csd_lock_wait()

Hi Marc,

On Wednesday 02 August 2017 02:14 PM, Marc Zyngier wrote:
> On 02/08/17 09:08, Will Deacon wrote:
>> Hi Pratyush,
>>
>> On Wed, Aug 02, 2017 at 09:01:19AM +0530, Pratyush Anand wrote:
>>> 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.
>>
>> When you say "also", which other kernel(s) show the problem? Is this a
>> recent regression? Which platform are you running on?
>>
>> It would be interesting to know what the other CPUs are doing, in particular
>> the target of the cross-call. Either it crashed spectacularly and didn't
>> unlock the csd lock, or the IPI somehow wasn't delivered.
>>
>> Do you see any other splats if you enable lock debugging?
> 
> Also, is that in a guest, or bare metal? If that's a guest, what's the
> host's kernel version?

Its a host.
-- 
Regards
Pratyush