Re: Crashes with 874bbfe600a6 in 3.18.25

From	Petr Mladek <pmladek@suse.com>
Newsgroups	linux.kernel
Subject	Re: Crashes with 874bbfe600a6 in 3.18.25
Date	2016-01-26 12:20 +0100
Message-ID	<qV9Pc-3ib-33@gated-at.bofh.it> (permalink)
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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.

Best Regards,
Petr

Thread

Crashes with 874bbfe600a6 in 3.18.25 Jan Kara <jack@suse.cz> - 2016-01-20 22:20 +0100
  Re: Crashes with 874bbfe600a6 in 3.18.25 Shaohua Li <shli@fb.com> - 2016-01-20 22:40 +0100
    Re: Crashes with 874bbfe600a6 in 3.18.25 Jan Kara <jack@suse.cz> - 2016-01-21 11:00 +0100
      Re: Crashes with 874bbfe600a6 in 3.18.25 Sasha Levin <sasha.levin@oracle.com> - 2016-01-21 14:40 +0100
      Re: Crashes with 874bbfe600a6 in 3.18.25 Sasha Levin <sasha.levin@oracle.com> - 2016-01-22 02:20 +0100
        Re: Crashes with 874bbfe600a6 in 3.18.25 Tejun Heo <tj@kernel.org> - 2016-01-22 17:10 +0100
          Re: Crashes with 874bbfe600a6 in 3.18.25 Ben Hutchings <ben@decadent.org.uk> - 2016-01-23 03:30 +0100
            Re: Crashes with 874bbfe600a6 in 3.18.25 Thomas Gleixner <tglx@linutronix.de> - 2016-01-23 17:20 +0100
              Re: Crashes with 874bbfe600a6 in 3.18.25 Jan Kara <jack@suse.cz> - 2016-01-26 10:40 +0100
                Re: Crashes with 874bbfe600a6 in 3.18.25 Thomas Gleixner <tglx@linutronix.de> - 2016-01-26 11:00 +0100
                Re: Crashes with 874bbfe600a6 in 3.18.25 Petr Mladek <pmladek@suse.com> - 2016-01-26 12:20 +0100
                Re: Crashes with 874bbfe600a6 in 3.18.25 Thomas Gleixner <tglx@linutronix.de> - 2016-01-26 14:20 +0100

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