linux-kernel - Re: Possible bug with mutex adaptative spinning

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Date:	Sat, 17 Apr 2010 08:01:32 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: Possible bug with mutex adaptative spinning

On Fri, 2010-04-16 at 23:27 +0200, Peter Zijlstra wrote:
> > If the owner is actually running, it may do so for a very long time. It
> > looks to me that everybody trying to take the mutex will thus spin and
> > never get out of the spin loop until the owner stops running.
> 
> The inner-most spin loop breaks out on need_resched():
> 
>                 if (task_thread_info(rq->curr) != owner || need_resched())
>                         return 0; 

You are right, this was only a problem in conjunction with the other bug
returning 1 all the time, causing us to ignore need_resched(). With
that fixed, it looks fine now.

Thanks !

Cheers,
Ben.


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