From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752194AbcHHKWV (ORCPT ); Mon, 8 Aug 2016 06:22:21 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:49887 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751985AbcHHKWU (ORCPT ); Mon, 8 Aug 2016 06:22:20 -0400 Date: Mon, 8 Aug 2016 12:22:13 +0200 From: Peter Zijlstra To: Bart Van Assche Cc: Oleg Nesterov , "mingo@kernel.org" , Andrew Morton , Johannes Weiner , Neil Brown , Michael Shaver , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs Message-ID: <20160808102213.GA6879@twins.programming.kicks-ass.net> References: <20160803181128.GH6879@twins.programming.kicks-ass.net> <11007730-3fa5-139a-8091-655743894ae8@sandisk.com> <20160803213006.GA11712@redhat.com> <17b65ff9-215f-ab74-9f5f-15dbd308d054@sandisk.com> <20160804140938.GB24652@twins.programming.kicks-ass.net> <16207b90-2e6c-fe23-1b4b-3763e5cf0384@sandisk.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <16207b90-2e6c-fe23-1b4b-3763e5cf0384@sandisk.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 05, 2016 at 10:41:33AM -0700, Bart Van Assche wrote: > On 08/04/2016 07:09 AM, Peter Zijlstra wrote: > >But I'd still like to understand where we loose the wakeup. > > My assumption is that __wake_up_common() and signal delivery happen > concurrently, that __wake_up_common() wakes up bit_wait_io() and that signal > delivery happens after bit_wait_io() has been woken up but before it tests > the signal pending state. That would be the exact scenario I drew a picture of, no? I'm still failing to see the hole there. Please draw a picture like that and illustrate the hole.