linux-kernel - Re: [patch 2/4] rt-mutex: Fix chain walk early wakeup bug

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Date:	Fri, 8 Jun 2007 09:18:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [patch 2/4] rt-mutex: Fix chain walk early wakeup bug


* Thomas Gleixner <tglx@...utronix.de> wrote:

> +++ linux-2.6.22-rc4/kernel/rtmutex.c	2007-06-08 01:39:38.000000000 +0200
> @@ -189,6 +189,19 @@ int rt_mutex_adjust_prio_chain(struct ta
>  	if (!waiter || !waiter->task)
>  		goto out_unlock_pi;
>  
> +	/*
> +	 * Check the orig_waiter state. After we dropped the locks,
> +	 * the previous owner of the lock might have released the lock
> +	 * and made us the pending owner:
> +	 */
> +	if (orig_waiter && !orig_waiter->task)
> +		goto out_unlock_pi;
> +
> +	/*
> +	 * Drop out, when the task has no waiters. Note,
> +	 * top_waiter can be NULL, when we are in the deboosting
> +	 * mode!
> +	 */
>  	if (top_waiter && (!task_has_pi_waiters(task) ||
>  			   top_waiter != task_top_pi_waiter(task)))
>  		goto out_unlock_pi;

nice fix! I'm wondering why we never triggered this case with in-kernel 
locks in -rt?

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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