Re: [PATCH] cgroup: Don't drop the cgroup_mutex in cgroup_rmdir

[Glauber Costa <glommer@parallels.com>]

On 07/20/2012 05:05 PM, Tejun Heo wrote:
> Hey, Peter.
> 
> On Fri, Jul 20, 2012 at 05:45:40PM +0200, Peter Zijlstra wrote:
>>> So, Peter, why does cpuset mangle with cgroup_mutex?  What guarantees
>>> does it need?  Why can't it work on "changed" notification while
>>> caching the current css like blkcg does?
>>
>> I've no clue sorry.. /me goes stare at this stuff.. Looks like something
>> Paul Menage did when he created cgroups. I'll have to have a hard look
>> at all that to untangle this. Not something obvious to me.
> 
> Yeah, it would be great if this can be untangled.  I really don't see
> any other reasonable way out of this circular locking mess.  If cpuset
> needs stable css association across certain period, the RTTD is
> caching the css by holding its ref and synchronize modifications to
> that cache, rather than synchronizing cgroup operations themselves.
> 
> Thanks.
> 
IIRC, cpuset can insert a task into an existing cgroup itself. Besides
that, it needs go have a stable vision of the cpumask used by all tasks
in the cgroup.

But this is what I remember from the top of my head, and I am still
officially on vacations....

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