Subject: Re: rcu_sched stall while waiting in csd_lock_wait()
To: Will Deacon <will.deacon@arm.com>, Pratyush Anand <panand@redhat.com>
References: <da7c56d6-066a-d123-f0cf-d9a3b97b001e@redhat.com>
 <20170802080827.GA15219@arm.com>
Cc: linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, mark.rutland@arm.com
From: Marc Zyngier <marc.zyngier@arm.com>
Organization: ARM Ltd
Message-ID: <f0fa028b-b690-2b85-ca01-3642ff883e30@arm.com>
Date: Wed, 2 Aug 2017 09:44:14 +0100
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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?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...