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Subject: Re: [PATCH 2.6.27-rc5 incremental re-resubmit] Fix itimer/many
	thread hang.
From: Frank Mayhar <fmayhar@google.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Roland McGrath <roland@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Oleg Nesterov <oleg@tv-sign.ru>
In-Reply-To: <20080930063313.GA23690@elte.hu>
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Content-Type: text/plain
Organization: Google, Inc.
Date: Tue, 30 Sep 2008 09:36:30 -0700
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On Tue, 2008-09-30 at 08:33 +0200, Ingo Molnar wrote:
> * Frank Mayhar <fmayhar@google.com> wrote:
> 
> >  /*
> >   * Return any ns on the sched_clock that have not yet been banked in
> >   * @p in case that task is currently running.
> > - *
> > - * Called with task_rq_lock() held on @rq.
> >   */
> > -static unsigned long long task_delta_exec(struct task_struct *p, struct rq *rq)
> > +unsigned long long task_delta_exec(struct task_struct *p)
> >  {
> > +	struct rq *rq;
> > +	unsigned long flags;
> > +	u64 ns = 0;
> > +
> >  	if (task_current(rq, p)) {
> >  		u64 delta_exec;
> 
> hmmm ... where do we get 'rq' from?
> 
> in v3 you did this:
> 
> -       rq = task_rq_lock(p, &flags);
> 
> which removed the deadlock but left us with a random uninitialized rq 
> variable ...

You know, I just knew I had a brain around here _somewhere_.

Weirdly, this didn't fall over on any of my testing.  The gods know what
it was actually doing, though.

I'm picking up tip/master right now and will test your fix for this
shortly.
-- 
Frank Mayhar <fmayhar@google.com>
Google, Inc.