linux-kernel - Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM

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Message-ID: <1306426823.27474.241.camel@e102391-lin.cambridge.arm.com>
Date:	Thu, 26 May 2011 17:20:23 +0100
From:	Marc Zyngier <Marc.Zyngier@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Yong Zhang <yong.zhang0@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Frank Rowand <frank.rowand@...sony.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()"
 locks up on ARM

On Thu, 2011-05-26 at 18:09 +0200, Peter Zijlstra wrote:
> On Thu, 2011-05-26 at 17:59 +0200, Peter Zijlstra wrote:
> > On Thu, 2011-05-26 at 17:45 +0200, Oleg Nesterov wrote:
> > > Stupid question. Can't we fix this problem if we do
> > > 
> > >         -       if (p == current)
> > >         +       if (cpu == raw_smp_processor_id())
> > > 
> > > ?
> > > 
> > > I forgot the rules... but iirc task_cpu(p) can't be changed under us?
> > 
> > Easy enough to test.. brain gave out again,. hold on ;-)
> 
> The below seems to run all-right so far, I'll let it run for a while.

Doesn't look very good here. The serial console basically locks up as
soon as the system gets busy, even if the kernel compilation seem to
progress at a decent pace.

	M.

-- 
Reality is an implementation detail.


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