linux-kernel - Re: [PATCH 2.6.27-rc5 incremental re-resubmit] Fix itimer/many thread hang.

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Message-Id: <1222792590.18031.9.camel@bobble.smo.corp.google.com>
Date:	Tue, 30 Sep 2008 09:36:30 -0700
From:	Frank Mayhar <fmayhar@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [PATCH 2.6.27-rc5 incremental re-resubmit] Fix itimer/many
	thread hang.

On Tue, 2008-09-30 at 08:33 +0200, Ingo Molnar wrote:
> * Frank Mayhar <fmayhar@...gle.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@...gle.com>
Google, Inc.

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