linux-kernel - Re: vmstat: On demand vmstat workers V8

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Message-ID: <alpine.DEB.2.11.1407291038160.21390@gentwo.org>
Date:	Tue, 29 Jul 2014 10:39:03 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Tejun Heo <tj@...nel.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	akpm@...ux-foundation.org, Gilad Ben-Yossef <gilad@...yossef.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, hughd@...gle.com,
	viresh.kumar@...aro.org, hpa@...or.com, mingo@...nel.org,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: vmstat: On demand vmstat workers V8

On Tue, 29 Jul 2014, Tejun Heo wrote:

> Hmmm, well, then it's something else.  Either a bug in workqueue or in
> the caller.  Given the track record, the latter is more likely.
> e.g. it looks kinda suspicious that the work func is cleared after
> cancel_delayed_work_sync() is called.  What happens if somebody tries
> to schedule it inbetween?

Here is yet another patch to also address this idea:

Subject: vmstat: Clear the work.func before cancelling delayed work

Looks strange to me but Tejun thinks this could do some good.
If this really is the right thing to do then cancel_delayed_work should
zap the work func itselt I think.

Signed-off-by: Christoph Lameter <cl@...ux.com>


Index: linux/mm/vmstat.c
===================================================================
--- linux.orig/mm/vmstat.c	2014-07-29 10:22:45.073884943 -0500
+++ linux/mm/vmstat.c	2014-07-29 10:34:45.083369228 -0500
@@ -1277,8 +1277,8 @@ static int vmstat_cpuup_callback(struct
 		break;
 	case CPU_DOWN_PREPARE:
 	case CPU_DOWN_PREPARE_FROZEN:
-		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
 		per_cpu(vmstat_work, cpu).work.func = NULL;
+		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
 		break;
 	case CPU_DOWN_FAILED:
 	case CPU_DOWN_FAILED_FROZEN:
--
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