linux-kernel - Re: [GIT PULL] workqueue fixes for v4.3-rc5

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Date:	Wed, 14 Oct 2015 12:57:31 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Shaohua Li <shli@...com>, linux-mm <linux-mm@...ck.org>
Subject: Re: [GIT PULL] workqueue fixes for v4.3-rc5

On Wed, 14 Oct 2015, Linus Torvalds wrote:

> I don't think it's normally a problem. But mm/vmstat.c clearly *is*
> confused, and uses both "schedule_delayed_work_on()" and
> "schedule_delayed_work()" for the same work.

Well yes the schedule_delayed_work_on() call is from another cpu and the
schedule_delayed_work() from the same. No confusion there.

vmstat_update() is run from the cpu where the diffs have to be updated and
if it needs to reschedule itself it relies on schedule_delayed_work() to
stay on the same cpu.

The vmstat_shepherd needs to start work items on remote cpus and therefore
uses xx_work_on().

And yes this relies on work items being executed on the same cpu unless
the queue is decleared to be UNBOUND which is not the case here.

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