| Re: bind() call in cgroup's css structure [message #45972 is a reply to message #45854] |
Tue, 10 April 2012 00:59  |
Li Zefan
Messages: 90
Registered: February 2008
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Member |
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Glauber Costa wrote:
> Hello Tejun,
>
> During your cgroup refactor, I was wondering if you have any plans to get rid of the bind() callback that is called when hierarchies are moved?
I planned to remove it long ago, and Paul M agreed. But after some time, I was
trying to make use of it in a patchset, which was used to fix the problem that
remount with different subsys bits will fail for !root cgroups.
>
> At least in tree, there seems to be no users for that.
> I actually planned to use it myself, to start or remove a jump label
> when cpuacct and cpu cgroups were comounted.
>
> Problem is, because we have some calls in the cpuset cgroup from inside the cpu hotplug handler, we end up taking the almighty cgroup_mutex from inside the cpu_hotplug.lock.
>
> jump labels take it in most arches through the get_online_cpus() function call. This means we effectively can't apply jump labels with the cgroup_mutex held, which is the case throughout the whole bind() call.
>
> All that explained, I figured I might as well ask before I attempted a solution to that myself: as much as populate(), bind seems to be one of the overly complicated callbacks, designed for a scenario in which everything can come and go at will, which is something we're trying to fix.
>
As we aim for single hierarchy, it defenitely should be removed.
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