linux-kernel - Re: Crashes with 874bbfe600a6 in 3.18.25

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Message-ID: <20160126093400.GV24938@quack.suse.cz>
Date:	Tue, 26 Jan 2016 10:34:00 +0100
From:	Jan Kara <jack@...e.cz>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ben Hutchings <ben@...adent.org.uk>, Tejun Heo <tj@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>, Jan Kara <jack@...e.cz>,
	Shaohua Li <shli@...com>, LKML <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, Daniel Bilik <daniel.bilik@...system.cz>
Subject: Re: Crashes with 874bbfe600a6 in 3.18.25

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.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR