Re: [PATCH] cpu_up: hold zonelists_mutex when build_all_zonelists

[Haicheng Li]

Andrew Morton wrote:
> On Thu, 20 May 2010 11:23:16 +0800
> Haicheng Li <haicheng.li@xxxxxxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/