linux-kernel - Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes

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Date:	Fri, 6 Jun 2014 04:53:14 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Brad Mouring <bmouring@...com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes

On Fri, 6 Jun 2014 07:40:10 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Thu, 5 Jun 2014, Steven Rostedt wrote:
> > On Wed, 4 Jun 2014 17:32:37 +0200 (CEST)
> > Thomas Gleixner <tglx@...utronix.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.
> 

Ah, the lock can be freed (out of memory that is). Why didn't you say
so in the first place ;-)

-- Steve
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