Re: [PATCH 4/6] cgroups: forbid pre_destroy callback to fail

From: Tejun Heo
Date: Thu Oct 18 2012 - 18:42:39 EST

Hello, Michal.

On Wed, Oct 17, 2012 at 03:30:46PM +0200, Michal Hocko wrote:
> Now that mem_cgroup_pre_destroy callback doesn't fail finally we can
> safely move on and forbit all the callbacks to fail. The last missing
> piece is moving cgroup_call_pre_destroy after cgroup_clear_css_refs so
> that css_tryget fails so no new charges for the memcg can happen.
> The callbacks are also called from within cgroup_lock to guarantee that
> no new tasks show up. We could theoretically call them outside of the
> lock but then we have to move after CGRP_REMOVED flag is set.
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>

So, the plan is to do something like the following once memcg is

Note that the patch is broken in a couple places but it does show the
general direction. I'd prefer if patch #3 simply makes pre_destroy()
return 0 and drop __DEPRECATED_clear_css_refs from mem_cgroup_subsys.
Then, I can pull the branch in and drop all the unnecessary cruft.


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