linux-kernel - Re: [PATCH 5/5] futex: fix miss ordered wakeups

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Message-ID: <alpine.LFD.1.10.0806130023440.3193@apollo.tec.linutronix.de>
Date:	Fri, 13 Jun 2008 00:43:38 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Walker <dwalker@...sta.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Ulrich Drepper <drepper@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 5/5] futex: fix miss ordered wakeups

On Thu, 12 Jun 2008, Daniel Walker wrote:

> 
> On Thu, 2008-06-12 at 21:55 +0200, Thomas Gleixner wrote:
> > Also your interpretation of the POSIX requirement is very
> > questionable:
> > 
> >  "If there are threads blocked on the mutex object referenced by mutex
> >  when pthread_mutex_unlock() is called, resulting in the mutex
> >  becoming available, the scheduling policy shall determine which
> >  thread shall acquire the mutex."
> 
> The key is "scheduling policy" .. When the mutex is un-blocked the next
> task to run is the same as if the scheduler was selecting tasks from the
> list of blocked tasks .. For Linux, that means the highest priority
> tasks should be selected.. So it's no more acceptable for the scheduler
> to priority invert some tasks than it is for the futex to do it.

Sigh, when do you actually get a gripe that the default futex
implementation does not and can not guarantee that at all and therefor
your "correctness" patch is as important as a bag of rice which
toopled over in China ?

Provide answers to the real questions I asked more than once: 

What's the real world problem ? Who cares about that - except you ?

Up to the point where you are actually able to come up with that
answers please direct your replies to /dev/null. That avoids that I
have to touch my .procmailrc.

Thanks,

	tglx
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