linux-kernel - Re: 4.2-rc5 rcu stalls.

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Message-ID: <20150805143813.GF7051@lerouge>
Date:	Wed, 5 Aug 2015 16:38:14 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Jones <davej@...emonkey.org.uk>,
	Sasha Levin <sasha.levin@...cle.com>,
	paulmck@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: 4.2-rc5 rcu stalls.

On Wed, Aug 05, 2015 at 09:18:57AM -0400, Dave Jones wrote:
> On Wed, Aug 05, 2015 at 02:37:59PM +0200, Frederic Weisbecker wrote:
>  > On Tue, Aug 04, 2015 at 08:12:50PM -0400, Dave Jones wrote:
>  > > On Tue, Aug 04, 2015 at 12:54:35AM -0400, Sasha Levin wrote:
>  > >  > On 08/03/2015 06:03 PM, Paul E. McKenney wrote:
>  > >  > >> > Ugh, that doesn't revert cleanly.  Got something handy ?
>  > >  > > I do not, but perhaps either Sasha or Frederic do.
>  > >  > 
>  > >  > I've attached a revert courtesy of Peter.
>  > > 
>  > > Thanks.  At first I thought this was doing the trick, but then I hit this again.
>  > > 
>  > > 
>  > > [23643.545873] INFO: rcu_preempt detected stalls on CPUs/tasks:
>  > 
>  > If it still happens after Sasha's revert, which basically revert all the offending
>  > patches related to preempt lately, then the reason might be elsewhere.
>  > 
>  > How hard was it to reproduce? I see 23000 secs in your dmesg logs which is around 6 hours.
> 
> yeah. That's why I thought it had fixed it up until that point.
> My subsequent overnight run hit a different bug (that unpinning an unpinned lock bug in the scheduler)
> so I haven't had it happen since.
> 
>  > Also did you just launch trinity? no specific options?
>  
> basically
> 
> while [ 1 ];
> do
>   trinity -N 1000000 -q -l off -C256 -a64 -x fsync -x fdatasync -x syncfs -x sync -P INET --enable-fds=sockets
>   sudo ipcrm -a
> done
> 
> (The ipcrm thing is needed for long runs or eventually you oom, because trinity lacks the cleanup smarts)

Ok, can I run that safely on my testbox without it eating some of my files or should
I use some special purposed guest?

Thanks!
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