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

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Date:	Fri, 6 Jun 2014 07:40:10 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
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 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.

Thanks,

	tglx
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