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

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Message-ID: <alpine.DEB.2.11.1408060908580.4346@gentwo.org>
Date:	Wed, 6 Aug 2014 09:12:39 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	akpm@...ux-foundation.org, Gilad Ben-Yossef <gilad@...yossef.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tejun Heo <tj@...nel.org>, 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,
	peterz@...radead.org
Subject: Re: vmstat: On demand vmstat workers V8

On Tue, 5 Aug 2014, Sasha Levin wrote:

> I can easily trigger it by cranking up the cpu hotplug code. Just try to
> frequently offline and online cpus, it should reproduce quickly.

Thats what I thought.

The test was done with this fix applied right?


Subject: vmstat ondemand: Fix online/offline races

Do not allow onlining/offlining while the shepherd task is checking
for vmstat threads.

On offlining a processor do the right thing cancelling the vmstat
worker thread if it exista and also exclude it from the shepherd
process checks.

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

Index: linux/mm/vmstat.c
===================================================================
--- linux.orig/mm/vmstat.c	2014-07-30 09:35:54.602662306 -0500
+++ linux/mm/vmstat.c	2014-07-30 09:43:07.109037043 -0500
@@ -1317,6 +1317,7 @@ static void vmstat_shepherd(struct work_
 {
 	int cpu;

+	get_online_cpus();
 	/* Check processors whose vmstat worker threads have been disabled */
 	for_each_cpu(cpu, cpu_stat_off)
 		if (need_update(cpu) &&
@@ -1325,6 +1326,7 @@ static void vmstat_shepherd(struct work_
 			schedule_delayed_work_on(cpu, &per_cpu(vmstat_work, cpu),
 				__round_jiffies_relative(sysctl_stat_interval, cpu));

+	put_online_cpus();

 	schedule_delayed_work(&shepherd,
 		round_jiffies_relative(sysctl_stat_interval));
@@ -1380,8 +1382,8 @@ static int vmstat_cpuup_callback(struct
 		break;
 	case CPU_DOWN_PREPARE:
 	case CPU_DOWN_PREPARE_FROZEN:
-		if (!cpumask_test_and_set_cpu(cpu, cpu_stat_off))
-			cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
+		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
+		cpumask_clear_cpu(cpu, cpu_stat_off);
 		break;
 	case CPU_DOWN_FAILED:
 	case CPU_DOWN_FAILED_FROZEN:
--
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