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SubjectRe: [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@linux.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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