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

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Message-Id: <1213277402.16459.25.camel@localhost.localdomain>
Date:	Thu, 12 Jun 2008 06:30:02 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, Ulrich Drepper <drepper@...il.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 5/5] futex: fix miss ordered wakeups


On Thu, 2008-06-12 at 10:56 +0200, Thomas Gleixner wrote:
> On Wed, 11 Jun 2008, Daniel Walker wrote:
> > Adds an additional function call to the sched_setscheduler to update the
> > waiter position of a task if it happens to be waiting on a futex. This
> > ensures that the kernel level waiter ordering is correctly maintained
> > based on the changed priority of the task.
> > 
> > I fixed the locking issue noticed by Thomas Gleixner.
> > 
> > This doesn't address userspace at all, only the kernel level wakeups and
> > kernel level ordering.
> > 
> > The additional locking added to the futex_wait function has no visible speed
> > impact, and only effects waiters which actual enter the kernel.
> 
> The additional locking is just broken and you did not even bother to
> test your changes with lockdep.

I ran it with lockdep enabled , I didn't get any warnings..

> Aside of this, these patches still add 100 lines of code to achieve
> nothing - as dicussed when you previously submitted your changes. 
> 
> Please stop wasting everyone's time with that.

It achieves correct ordering of the futex waiters inside the kernel,
that is in fact _something_ ..

Daniel


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