From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754780AbaIBQIv (ORCPT ); Tue, 2 Sep 2014 12:08:51 -0400 Received: from mail-vc0-f176.google.com ([209.85.220.176]:63991 "EHLO mail-vc0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753526AbaIBQIt (ORCPT ); Tue, 2 Sep 2014 12:08:49 -0400 MIME-Version: 1.0 In-Reply-To: <5dfbace37c434be58ed26ea524aa0675@AM3PR06MB388.eurprd06.prod.outlook.com> References: <5dfbace37c434be58ed26ea524aa0675@AM3PR06MB388.eurprd06.prod.outlook.com> Date: Tue, 2 Sep 2014 09:08:48 -0700 X-Google-Sender-Auth: NKq6dbpR63VTyoCbPBe93XipauQ Message-ID: Subject: Re: Race condition in HR timers that cause double insertion and hard lockup -- all latest versions From: Linus Torvalds To: Itzcak Pechtalt , Thomas Gleixner Cc: "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 2, 2014 at 8:45 AM, Itzcak Pechtalt wrote: > > I opened a bug in https://bugzilla.kernel.org/show_bug.cgi?id=83601 for this subject with full description. > There is also a short fix patch for kernel/hrtimer.c file. > Even if this bug occurs rary, however it resolves system hard lockup option. The patch is whitespace-damaged, but with a small oneliner like this that doesn't much matter (the timer files moved to kernel/time/ during this merge window, so the patch wouldn't apply as-is anyway). It needs a sign-off (see Documentation/SubmittingPatches), but even more importantly it needs to go to the right people for double-checking. But the patch is more broken than whitespace and even lack of sign-off. It cannot even have compiled. I'm assuming "timer_state" was intended to be "timer->state". Also, every caller but one already has "HRTIMER_STATE_CALLBACK" set unconditionally or to the old state in "newstate", so I suspect if this patch is the real fix (which I'll leave for Thomas to comment more on), afaik the actual problem can only happen through migrate_hrtimer_list() which uconditionally sets the whole state to HRTIMER_STATE_MIGRATE. Thomas? Leaving damaged patch quoted below. Linus > I suspect that it was targeted by mistake to not active list (timers_realtime-clock@kernel-bugs.osdl.org). > Following is the fix patch based on kernel 3.16.1 (just simple): > diff -uNr a/kernel/hrtimer.c b/kernel/hrtimer.c > --- a/kernel/hrtimer.c 2014-08-31 20:59:52.177452123 +0300 > +++ b/kernel/hrtimer.c 2014-08-31 21:02:14.972166540 +0300 > @@ -941,7 +941,7 @@ > if (!timerqueue_getnext(&base->active)) > base->cpu_base->active_bases &= ~(1 << base->index); > out: > - timer->state = newstate; > + timer->state = (newstate | (timer_state & HRTIMER_STATE_CALLBACK)); > } > > /* > > Is there a chance for this patch fix to insert into next kernel release? > > Thanks > > Itzcak Pechtalt >