Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755398AbbLKLkW (ORCPT ); Fri, 11 Dec 2015 06:40:22 -0500 Received: from casper.infradead.org ([85.118.1.10]:44528 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755477AbbLKLkD (ORCPT ); Fri, 11 Dec 2015 06:40:03 -0500 Date: Fri, 11 Dec 2015 12:39:59 +0100 From: Peter Zijlstra To: Paul Turner Cc: NeilBrown , Linus Torvalds , Thomas Gleixner , LKML , Mike Galbraith , Ingo Molnar , Peter Anvin , vladimir.murzin@arm.com, linux-tip-commits@vger.kernel.org, jstancek@redhat.com, Oleg Nesterov Subject: Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers Message-ID: <20151211113959.GI6356@twins.programming.kicks-ass.net> References: <20151201130404.GL3816@twins.programming.kicks-ass.net> <20151208104712.GJ6356@twins.programming.kicks-ass.net> <87zixkph0m.fsf@notabene.neil.brown.name> <20151209074033.GF6357@twins.programming.kicks-ass.net> <87si3bpaxy.fsf@notabene.neil.brown.name> <20151210130948.GW6356@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 1610 Lines: 49 On Fri, Dec 11, 2015 at 03:30:33AM -0800, Paul Turner wrote: > > Blergh, all I've managed to far is to confuse myself further. Even > > something like the original (+- the EINTR) should work when we consider > > the looping, even when mixed with an occasional spurious wakeup. > > > > > > int bit_wait() > > { > > if (signal_pending_state(current->state, current)) > > return -EINTR; > > schedule(); > > } So I asked Vladimir to test that (simply changing the return from 1 to -EINTR) and it made his fail much less likely but it still failed in the same way. So I'm fairly sure I'm still missing something :/ > Hugh asked me about this after seeing a crash, here's another exciting > way in which the current code breaks -- this one actually quite > serious: Yep, this got reported by Jan and I did kick myself for that. > Peter's proposed follow-up above looks strictly more correct. We need > to evaluate the potential existence of a signal, *after* we return > from schedule, but in the context of the state which we previously > _entered_ schedule() on. > > Reviewed-by: Paul Turner Right, its maybe a bit overkill, but at this point I'm a tad conservative/paranoid. Vladimir, Jan could you both please that patch? lkml.kernel.org/r/20151208104712.GJ6356@twins.programming.kicks-ass.net Thanks! -- 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/