linux-kernel - Re: [PATCH 2/3 v2] futex: avoid double wake up in futex

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Message-ID: <20150416101637.GC5029@twins.programming.kicks-ass.net>
Date:	Thu, 16 Apr 2015 12:16:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Davidlohr Bueso <dave@...olabs.net>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Darren Hart <darren@...art.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	fredrik.markstrom@...driver.com,
	Manfred Spraul <manfred@...orfullife.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 2/3 v2] futex: avoid double wake up in futex_wake() on -RT

On Thu, Apr 16, 2015 at 11:19:41AM +0200, Thomas Gleixner wrote:
> So any code which does not handle a spurious wakeup is broken
> independent of the futex changes. So really nothing to worry about.

Back when we did this:

 http://lkml.iu.edu/hypermail/linux/kernel/1109.1/01941.html
 http://lkml.iu.edu/hypermail/linux/kernel/1109.1/01943.html

Things came apart -- notably sysvsems.

And yes its true that anything not dealing with spuriuos wakups is
borken, but there's still quite a lot of borken out there, although I
think we fixed all the really common ones.

But if we decide we want to go do this, I'd propose we reintroduce this
delayed wake list thing again.
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