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Message-ID: <alpine.LFD.1.10.0805081156450.3318@apollo.tec.linutronix.de> Date: Thu, 8 May 2008 12:06:18 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Daniel Walker <dwalker@...sta.com> cc: Pierre Peiffer <peifferp@...il.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: futex: priority wakeup miss ordering On Wed, 7 May 2008, Daniel Walker wrote: > > from commit ec92d08292d3e9b0823eba138a4564d2d39f25c7 > > The wakeup ordering should be in priority order. However if the priority > of a task is modified while it's waiting on the futex you will get an > out of order wakeup. > > If you use a priority inheriting mutex this is correct. It's because the > rtmutex hooks into sched_setscheduler to catch any priority changes, > then re-queues with the new priority.. But the futex doesn't have this > hook. > > Was this intentionally left out of this priority wake up patch? I > thought I would let you know in case you had a specific reason for not > handling this.. IIRC this has been discussed before. The priority ordering of the plain mutex waiters is an optimization without guarantees of correctness across a priority change. It's simply not worth the additional complexity and overhead for that corner case. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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