Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755620Ab1EZKzQ (ORCPT ); Thu, 26 May 2011 06:55:16 -0400 Received: from canuck.infradead.org ([134.117.69.58]:50149 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757139Ab1EZKzO convert rfc822-to-8bit (ORCPT ); Thu, 26 May 2011 06:55:14 -0400 X-Greylist: delayed 1295 seconds by postgrey-1.27 at vger.kernel.org; Thu, 26 May 2011 06:55:14 EDT Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM From: Peter Zijlstra To: Yong Zhang Cc: Marc Zyngier , Ingo Molnar , Frank Rowand , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Oleg Nesterov In-Reply-To: References: <1306260792.27474.133.camel@e102391-lin.cambridge.arm.com> <1306272750.2497.79.camel@laptop> <1306343335.21578.65.camel@twins> <1306358128.21578.107.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 26 May 2011 12:32:59 +0200 Message-ID: <1306405979.1200.63.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1182 Lines: 26 On Thu, 2011-05-26 at 15:29 +0800, Yong Zhang wrote: > > Figuring out why the existing condition failed > > Seems 'current' will change before/after switch_to since it's derived from > sp register. > So that means if interrupt come before we switch sp, 'p == current' will > catch it, but if interrupt comes after we switch sp, we will lose a wake up. Well, loosing a wakeup isn't the problem here (although it would be a problem), the immediate problem is that we're getting stuck (life-locked) in that while (p->on_cpu) loop. But yes, I think that explains it, if the interrupts hits context_switch() after current was changed but before clearing p->on_cpu, we would life-lock in interrupt context. Now we could of course go add in_interrupt() checks there, but that would make this already fragile path more interesting, so I think I'll stick with the proposed patch -- again provided it actually works. Marc, any word on that? -- 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/