linux-kernel - Re: [PATCH] cpu_up: hold zonelists_mutex when build_all

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Date:	Tue, 25 May 2010 13:05:50 +0800
From:	Haicheng Li <haicheng.li@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>, andi.kleen@...el.com,
	cl@...ux-foundation.org, fengguang.wu@...el.com, mel@....ul.ie,
	tj@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	minskey guo <chaohong.guo@...el.com>
Subject: Re: [PATCH] cpu_up: hold zonelists_mutex when build_all_zonelists

Andrew Morton wrote:
> On Thu, 20 May 2010 11:23:16 +0800
> Haicheng Li <haicheng.li@...ux.intel.com> wrote:
> 
>> Here is another issue, we should always hold zonelists_mutex when calling build_all_zonelists
>> unless system_state == SYSTEM_BOOTING.
> 
> Taking a global mutex in the cpu-hotplug code is worrisome.  Perhaps
> because of the two years spent weeding out strange deadlocks between
> cpu-hotplug and cpufreq.
> 
> Has this change been carefully and fully tested with lockdep enabled
> (please)?
Yes, Andrew. I've tested it with lockdep enabled, and there was *no*
issue found for this change in my testing.

My test box: CPUs on node 1~3 are all offlined (16 cpus per node).
Here are my test steps:
on tty0:
# cd /sys/devices/system/node/node1
# for i in cpu*; do echo 1 > $i/online; done

on tty1:
# cd /sys/devices/system/node/node2
# for i in cpu*; do echo 1 > $i/online; done

on tty2:
# cd /sys/devices/system/node/node3
# for i in cpu*; do echo 1 > $i/online; done

on tty3:
# cat zonelist

	#! /bin/bash
	set -x
	while ((1)); do
		echo n > /proc/sys/vm/numa_zonelist_order
		sleep 10
		echo z > /proc/sys/vm/numa_zonelist_order
		sleep 10
	done

# ./zonelist

Besides, I also ran some cpu online/offline tests from LTP/cpu_hotplug test suites.
They worked fine too.

>> --- a/kernel/cpu.c
>> +++ b/kernel/cpu.c
>> @@ -357,8 +357,11 @@ int __cpuinit cpu_up(unsigned int cpu)
>>                  return -ENOMEM;
>>          }
>>
>> -       if (pgdat->node_zonelists->_zonerefs->zone == NULL)
>> +       if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
>> +               mutex_lock(&zonelists_mutex);
>>                  build_all_zonelists(NULL);
>> +               mutex_unlock(&zonelists_mutex);
>> +       }
> 
> Your email client is performing space-stuffing and it replaces tabs
> with spaces.  This requires me to edit the patches rather a lot,
> which is dull.

Really sorry for the inconvenience to you. I'll pay more attention
next time. thank you!

-haicheng
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