From: Thomas Gleixner <tglx@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Jan Kara <jack@suse.cz>, Ben Hutchings <ben@decadent.org.uk>,
Tejun Heo <tj@kernel.org>, 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: Tue, 26 Jan 2016 14:09:36 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1601261352010.3886@nanos> (raw)
In-Reply-To: <20160126111438.GA731@pathway.suse.cz>
[-- Attachment #1: Type: TEXT/PLAIN, Size: 2333 bytes --]
On Tue, 26 Jan 2016, Petr Mladek wrote:
> On Tue 2016-01-26 10:34:00, Jan Kara wrote:
> > On Sat 23-01-16 17:11:54, Thomas Gleixner wrote:
> > > On Sat, 23 Jan 2016, Ben Hutchings wrote:
> > > > On Fri, 2016-01-22 at 11:09 -0500, Tejun Heo wrote:
> > > > > > Looks like it requires more than trivial backport (I think). Tejun?
> > > > >
> > > > > The timer migration has changed quite a bit. Given that we've never
> > > > > seen vmstat work crashing in 3.18 era, I wonder whether the right
> > > > > thing to do here is reverting 874bbfe600a6 from 3.18 stable?
> > > >
> > > > It's not just 3.18 that has this; 874bbfe600a6 was backported to all
> > > > stable branches from 3.10 onward. Only the 4.2-ckt branch has
> > > > 22b886dd10180939.
> > >
> > > 22b886dd10180939 fixes a bug which was introduced with the timer wheel
> > > overhaul in 4.2. So only 4.2/3 should have it backported.
> >
> > Thanks for explanation. So do I understand right that timers are always run
> > on the calling CPU in kernels prior to 4.2 and thus commit 874bbfe600a6 (to
> > run timer for delayed work on the calling CPU) doesn't make sense there? If
> > that is true than reverting the commit from older stable kernels is
> > probably the easiest way to resolve the crashes.
>
> The commit 874bbfe600a6 ("workqueue: make sure delayed work run in
> local cpu") forces the timer to run on the local CPU. It might be correct
> for vmstat. But I wonder if it might break some other delayed work
> user that depends on running on different CPU.
The default of add_timer() is to run on the current cpu. It only moves the
timer to a different cpu when the power saving code says so. So 874bbfe600a6
enforces that the timer runs on the cpu on which queue_delayed_work() is
called, but before that commit it was likely that the timer was queued on the
calling cpu. So there is nothing which can depend on running on a different
CPU, except callers of queue_delayed_work_on() which provide the target cpu
explicitely. 874bbfe600a6 does not affect those callers at all.
Now, what's different is:
+ if (cpu == WORK_CPU_UNBOUND)
+ cpu = raw_smp_processor_id();
dwork->cpu = cpu;
So before that change dwork->cpu was set to WORK_CPU_UNBOUND. Now it's set to
the current cpu, but I can't see how that matters.
Thanks,
tglx
next prev parent reply other threads:[~2016-01-26 13:10 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 [this message]
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
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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