linux-kernel - Re: [RFC][PATCH RT] rtmutex: Use raw_spin_trylock() in rt_mutex

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Message-ID: <1356026521.5896.55.camel@gandalf.local.home>
Date:	Thu, 20 Dec 2012 13:02:01 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <cbe@...dl.org>,
	Clark Williams <clark@...hat.com>,
	John Kacur <jkacur@...hat.com>,
	Mike Galbraith <bitbucket@...ine.de>
Subject: Re: [RFC][PATCH RT] rtmutex: Use raw_spin_trylock() in
 rt_mutex_slowlock() to ease possible live locks

On Wed, 2012-12-19 at 20:31 -0500, Steven Rostedt wrote:

Talking with Thomas, the proper solution is:

> Then we have this lovely code:
> 
> block/blk-ioc.c: put_io_context_active()
> 
> retry:
>         spin_lock_irqsave_nested(&ioc->lock, flags, 1);
>         hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node) {
>                 if (icq->flags & ICQ_EXITED)
>                         continue;
>                 if (spin_trylock(icq->q->queue_lock)) {
>                         ioc_exit_icq(icq);
>                         spin_unlock(icq->q->queue_lock);
>                 } else {
>                         spin_unlock_irqrestore(&ioc->lock, flags);
>                         cpu_relax();

s/cpu_relax/cpu_chill/

-- Steve

>                         goto retry;
>                 }
>         }
> 


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