Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758177Ab1EZRvR (ORCPT ); Thu, 26 May 2011 13:51:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27473 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758012Ab1EZRvQ (ORCPT ); Thu, 26 May 2011 13:51:16 -0400 Date: Thu, 26 May 2011 19:49:03 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Marc Zyngier , Yong Zhang , Ingo Molnar , Frank Rowand , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM Message-ID: <20110526174903.GA19853@redhat.com> References: <1306405979.1200.63.camel@twins> <1306407759.27474.207.camel@e102391-lin.cambridge.arm.com> <1306409575.1200.71.camel@twins> <1306412511.1200.90.camel@twins> <20110526154508.GA13788@redhat.com> <1306425584.2497.81.camel@laptop> <1306426148.2497.83.camel@laptop> <20110526170422.GA18413@redhat.com> <1306430264.2497.88.camel@laptop> <1306430633.2497.91.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1306430633.2497.91.camel@laptop> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1053 Lines: 35 On 05/26, Peter Zijlstra wrote: > > It has the extra cpu == smp_processor_id() check, but I'm not sure this > whole case is worth the trouble. Agreed, this case is very unlikely. Perhaps it makes the code more clear though, up to you. But, if we keep this check, > @@ -2636,9 +2636,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > * to spin on ->on_cpu if p is current, since that would > * deadlock. > */ > - if (p == current) { > - ttwu_queue(p, cpu); > - goto stat; > + if (cpu == smp_processor_id()) { > + struct rq *rq; > + > + rq = __task_rq_lock(p); > + if (p->on_cpu) { > + ttwu_activate(rq, p, ENQUEUE_WAKEUP); > + ttwu_do_wakeup(rq, p, wake_flags); > + __task_rq_unlock(rq); then why we re-check ->on_cpu? Just curious. Oleg. -- 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/