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Date: Fri, 6 Jun 2014 07:44:23 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Steven Rostedt <rostedt@goodmis.org>
cc: Brad Mouring <bmouring@ni.com>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Clark Williams <williams@redhat.com>
Subject: Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes
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On Fri, 6 Jun 2014, Thomas Gleixner wrote:
> On Thu, 5 Jun 2014, Steven Rostedt wrote:
> > On Wed, 4 Jun 2014 17:32:37 +0200 (CEST)
> > Thomas Gleixner <tglx@linutronix.de> wrote:
> > +	/*
> > +	 * When we dropped the spinlocks, if the owner of the lock we
> > +	 * are currently processing changed since we chain walked
> > +	 * to that lock, we are done with the chain walk. The previous
> > +	 * owner was obviously running to release it.
> > +	 */
> > +	if (lock && rt_mutex_owner(lock) != task)
> > +		goto out_unlock_pi;
> 
> NO. You CANNOT derefernce lock after dropping the locks. It might be
> gone already.

The only information we can check is, whether @task changed the
blocked on lock, really.

Thanks,

	tglx