From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752638AbaEEPMk (ORCPT ); Mon, 5 May 2014 11:12:40 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:57101 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751826AbaEEPMi convert rfc822-to-8bit (ORCPT ); Mon, 5 May 2014 11:12:38 -0400 Date: Mon, 5 May 2014 17:12:28 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, khilman@linaro.org, tglx@linutronix.de, axboe@fb.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:timers/nohz] nohz: Move full nohz kick to its own IPI Message-ID: <20140505151228.GR26782@laptop.programming.kicks-ass.net> References: <20140505123706.GP17778@laptop.programming.kicks-ass.net> <20140505133113.GD1429@laptop.programming.kicks-ass.net> <20140505150356.GB2099@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20140505150356.GB2099@localhost.localdomain> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Note the current ordering: > > cmpxchg(&qsd->pending, 0, 1) get ipi > csd_lock(qsd->csd) xchg(&qsd->pending, 1) > send ipi csd_unlock(qsd->csd) > > > So there shouldn't be racing updaters. Also ipi sender shouldn't > race with ipi receiver, the update shouldn't always eventually see > the unlock happening. Yeah, I've not spotted how this particular train wreck happens either. The problem is reproduction, it took me 9 hours to confirm I could reproduce the problem on my machine. So how long to I run it with this patch reverted to show its gone..