From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Tejun Heo <tj@kernel.org>, Michal Hocko <mhocko@kernel.org>,
Jiri Slaby <jslaby@suse.cz>, Petr Mladek <pmladek@suse.com>,
Jan Kara <jack@suse.cz>, Ben Hutchings <ben@decadent.org.uk>,
Sasha Levin <sasha.levin@oracle.com>, Shaohua Li <shli@fb.com>,
LKML <linux-kernel@vger.kernel.org>,
stable@vger.kernel.org, Daniel Bilik <daniel.bilik@neosystem.cz>
Subject: Re: Crashes with 874bbfe600a6 in 3.18.25
Date: Thu, 04 Feb 2016 12:07:16 +0100 [thread overview]
Message-ID: <1454584036.3407.121.camel@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1602041130380.25254@nanos>
On Thu, 2016-02-04 at 11:46 +0100, Thomas Gleixner wrote:
> On Thu, 4 Feb 2016, Mike Galbraith wrote:
> > I'm also wondering why 22b886dd only applies to kernels >= 4.2.
> >
> >
> > Regardless of the previous CPU a timer was on, add_timer_on()
> > currently simply sets timer->flags to the new CPU. As the caller must
> > be seeing the timer as idle, this is locally fine, but the timer
> > leaving the old base while unlocked can lead to race conditions as
> > follows.
> >
> > Let's say timer was on cpu 0.
> >
> > cpu 0 cpu 1
> > -----------------------------------------------------------------------------
> > del_timer(timer) succeeds
> > del_timer(timer)
> > lock_timer_base(timer) locks cpu_0_base
> > add_timer_on(timer, 1)
> > spin_lock(&cpu_1_base->lock)
> > timer->flags set to cpu_1_base
> > operates on @timer operates on @timer
> >
> >
> > What's the difference between...
> > timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
> > and...
> > timer_set_base(timer, base);
> >
> > ...that makes that fix unneeded prior to 4.2? We take the same locks
> > in < 4.2 kernels, so seemingly both will diddle concurrently above.
>
> Indeed, you are right.
Whew, thanks for confirming, looking for what the hell I was missing
wasn't going well at all, ate most of my day.
> The same can happen on pre 4.2, just the fix does not apply as we changed the
> internals how the base is managed in the timer itself. Backport below.
Exactly what I did locally.
-Mike
next prev parent reply other threads:[~2016-02-04 11:07 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-20 21:19 Crashes with 874bbfe600a6 in 3.18.25 Jan Kara
2016-01-20 21:39 ` Shaohua Li
2016-01-21 9:52 ` Jan Kara
2016-01-21 13:29 ` Sasha Levin
2016-01-22 1:10 ` Sasha Levin
2016-01-22 16:09 ` Tejun Heo
2016-01-23 2:20 ` Ben Hutchings
2016-01-23 16:11 ` Thomas Gleixner
2016-01-26 9:34 ` Jan Kara
2016-01-26 9:49 ` Thomas Gleixner
2016-01-26 11:14 ` Petr Mladek
2016-01-26 13:09 ` Thomas Gleixner
2016-02-03 9:35 ` Jiri Slaby
2016-02-03 10:41 ` Thomas Gleixner
2016-02-03 12:28 ` Michal Hocko
2016-02-03 16:24 ` Tejun Heo
2016-02-03 16:48 ` Michal Hocko
2016-02-03 16:59 ` Tejun Heo
2016-02-04 6:37 ` Michal Hocko
2016-02-04 7:40 ` Michal Hocko
2016-02-03 17:01 ` Mike Galbraith
2016-02-03 17:06 ` Tejun Heo
2016-02-03 17:13 ` Mike Galbraith
2016-02-03 17:15 ` Tejun Heo
2016-02-04 2:00 ` Mike Galbraith
2016-02-05 16:49 ` Tejun Heo
2016-02-05 20:47 ` Mike Galbraith
2016-02-05 20:54 ` Tejun Heo
2016-02-05 20:59 ` Mike Galbraith
2016-02-05 21:06 ` Tejun Heo
2016-02-06 13:07 ` Henrique de Moraes Holschuh
2016-02-07 5:19 ` Mike Galbraith
2016-02-07 5:59 ` Mike Galbraith
2016-02-09 15:31 ` Mike Galbraith
2016-02-09 16:39 ` Linus Torvalds
2016-02-09 16:50 ` Tejun Heo
2016-02-09 17:04 ` Mike Galbraith
2016-02-09 17:54 ` Tejun Heo
2016-02-09 17:56 ` Mike Galbraith
2016-02-09 18:02 ` Mike Galbraith
2016-02-09 18:27 ` Tejun Heo
2016-02-09 17:04 ` Linus Torvalds
2016-02-09 17:51 ` Tejun Heo
2016-02-09 18:06 ` Linus Torvalds
2016-02-04 10:04 ` Mike Galbraith
2016-02-04 10:46 ` Thomas Gleixner
2016-02-04 11:07 ` Mike Galbraith [this message]
2016-02-04 11:20 ` Jan Kara
2016-02-04 16:39 ` Daniel Bilik
2016-02-05 2:40 ` Mike Galbraith
2016-02-05 8:11 ` Daniel Bilik
2016-02-05 8:33 ` Mike Galbraith
2016-02-03 18:46 ` Thomas Gleixner
2016-02-03 19:01 ` Tejun Heo
2016-02-03 19:05 ` Thomas Gleixner
2016-02-03 19:15 ` Tejun Heo
2016-02-05 5:44 ` Mike Galbraith
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