Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754810AbbLKNJY (ORCPT ); Fri, 11 Dec 2015 08:09:24 -0500 Received: from mx4-phx2.redhat.com ([209.132.183.25]:38469 "EHLO mx4-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750987AbbLKNJV (ORCPT ); Fri, 11 Dec 2015 08:09:21 -0500 Date: Fri, 11 Dec 2015 08:08:36 -0500 (EST) From: Jan Stancek To: Peter Zijlstra Cc: Paul Turner , NeilBrown , Linus Torvalds , Thomas Gleixner , LKML , Mike Galbraith , Ingo Molnar , Peter Anvin , vladimir murzin , linux-tip-commits@vger.kernel.org, Oleg Nesterov Message-ID: <285059043.27110857.1449839316960.JavaMail.zimbra@redhat.com> In-Reply-To: <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> <20151211113959.GI6356@twins.programming.kicks-ass.net> Subject: Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.34.26.57] X-Mailer: Zimbra 8.0.6_GA_5922 (ZimbraWebClient - FF38 (Linux)/8.0.6_GA_5922) Thread-Topic: locking/core] sched/wait: Fix signal handling in bit wait helpers Thread-Index: lkOpKyTgsO6dS2nuR1nO895Q/1Y46A== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2663 Lines: 75 ----- Original Message ----- > From: "Peter Zijlstra" > To: "Paul Turner" > Cc: "NeilBrown" , "Linus Torvalds" , "Thomas Gleixner" > , "LKML" , "Mike Galbraith" , "Ingo Molnar" > , "Peter Anvin" , "vladimir murzin" , > linux-tip-commits@vger.kernel.org, jstancek@redhat.com, "Oleg Nesterov" > Sent: Friday, 11 December, 2015 12:39:59 PM > Subject: Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers > > 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 This appears to exactly match patch I tested against v4.4-rc4 here: http://marc.info/?l=linux-mm&m=144950957622869&w=2 Anyway, I repeated the test with v4.4-rc4-113-g0bd0f1e as base. Results look good. With patch applied, I can't trigger "kernel BUG at mm/filemap.c:238!" anymore. Regards, Jan > > > 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/