Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760968AbZJMSqM (ORCPT ); Tue, 13 Oct 2009 14:46:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760954AbZJMSqL (ORCPT ); Tue, 13 Oct 2009 14:46:11 -0400 Received: from www.tglx.de ([62.245.132.106]:44688 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760087AbZJMSqK (ORCPT ); Tue, 13 Oct 2009 14:46:10 -0400 Date: Tue, 13 Oct 2009 20:45:03 +0200 (CEST) From: Thomas Gleixner To: Darren Hart cc: Blaise Gassend , Jeremy Leibs , Peter Zijlstra , "lkml," Subject: Re: ERESTARTSYS escaping from sem_wait with RTLinux patch In-Reply-To: <4AD49928.40600@us.ibm.com> Message-ID: References: <1255165747.6385.117.camel@doodleydee> <92be2ef30910102248t70d5e683tc525580fbf902af1@mail.gmail.com> <4AD33A4D.4070006@us.ibm.com> <1255384010.10236.123.camel@lts.willowgarage.com> <4AD3BD57.6080703@us.ibm.com> <4AD3D6AE.2050609@us.ibm.com> <4AD3FFB0.5030405@us.ibm.com> <4AD4080C.20703@us.ibm.com> <1255424204.12737.233.camel@doodleydee> <4AD49928.40600@us.ibm.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1244 Lines: 27 On Tue, 13 Oct 2009, Darren Hart wrote: > Talking with Thomas a bit more we're not sure the patch that introduced this > lockless waking actually does any good, as the normal wakeup path doesn't take > the hb->lock anyway, it's more likely the contention was due to an app like > this that wakes a task and almost immediately puts it back to sleep on a futex > before the waker has a chance to drop the hb->lock. The patch was done before we restructured the wakeup code in mainline and it's not necessary anymore. > The futex wake-up path is complicated enough as it is, in my personal opinion, > we are better off dropping the "lockless wake-up" patch and removing the race > and simplifying the wake-up path at the same time. Nevertheless we need graceful handling of spurious wakeups in the waiter code. I'm working on a fix for mainline, which will be in the next -rt release as well (after I reverted the no longer valid wakeup optimization) Thanks folks for debugging that. tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/