linux-kernel - Re: [patch 1/5] Fix timeout bug in rtmutex in 2.6.18-rt

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Date:	Mon, 13 Nov 2006 11:39:27 +0100 (CET)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Esben Nielsen <nielsen.esben@...glemail.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch 1/5] Fix timeout bug in rtmutex in 2.6.18-rt

On Fri, 10 Nov 2006, Ingo Molnar wrote:

>
> on SMP i had to remove this assert:
>
> Index: linux/kernel/rtmutex.c
> ===================================================================
> --- linux.orig/kernel/rtmutex.c
> +++ linux/kernel/rtmutex.c
> @@ -823,7 +823,7 @@ rt_spin_lock_slowunlock(struct rt_mutex
> 	}
> 	wakeup_next_waiter(lock, 1);
> 	spin_unlock_irqrestore(&lock->wait_lock, flags);
> -	BUG_ON(current->boosting_prio != MAX_PRIO);
> +//	BUG_ON(current->boosting_prio != MAX_PRIO);
> 	/* Undo pi boosting.when necessary */
> 	rt_mutex_adjust_prio(current);
> }
>
> because it triggered almost immediately after bootup.
>

Hmm, boosting_prio should be MAX_PRIO at that point. boosting_prio should
only be different from MAX_PRIO while a task is trying to lock a mutex - 
i.e. while it is in a *_slowlock() function.

On which kernel have you applied the patch?

I am looking at 2.6.18-rt6 and trying to see if there is a race conditions.
I can't see it that easily (or I would probably have seen it already :-). 
task->boosting_prio is not set when task->pi_lock is not taken. And then 
it is only set to something else than MAX_PRIO if task->pi_blocked_on is 
set.

> 	Ingo
>

Esben
-
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