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Subject: Re: Crashes with 874bbfe600a6 in 3.18.25
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>, Jiri Slaby <jslaby@suse.cz>,
	Thomas Gleixner <tglx@linutronix.de>,
	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>
Date: Wed, 03 Feb 2016 18:13:15 +0100
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On Wed, 2016-02-03 at 12:06 -0500, Tejun Heo wrote:
> On Wed, Feb 03, 2016 at 06:01:53PM +0100, Mike Galbraith wrote:
> > Hm, so it's ok to queue work to an offline CPU?  What happens if it
> > doesn't come back for an eternity or two?
> 
> Right now, it just loses affinity.  A more interesting case is a cpu
> going offline whlie work items bound to the cpu are still running and
> the root problem is that we've never distinguished between affinity
> for correctness and optimization and thus can't flush or warn on the
> stagglers.  The plan is to ensure that all correctness users specify
> the CPU explicitly.  Once we're there, we can warn on illegal usages.

Ah, and the rest (the vast majority) can then be safely deflected away
from nohz_full cpus.

	-Mike