On 10/29/2012 06:04 PM, Glauber Costa wrote: > On 10/26/2012 03:37 PM, Michal Hocko wrote: >> Now that mem_cgroup_pre_destroy callback doesn't fail (other than a race >> with a task attach resp. child group appears) 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. >> We cannot, however, move cgroup_call_pre_destroy right after because we >> cannot call mem_cgroup_pre_destroy with the cgroup_lock held (see >> 3fa59dfb cgroup: fix potential deadlock in pre_destroy) so we have to >> move it after the lock is released. >> > > If we don't have the cgroup lock held, how safe is the following > statement in mem_cgroup_reparent_charges(): > > if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children)) > return -EBUSY; > > ? > > IIUC, although this is not generally safe, but it would be safe here > because at this point we are expected to had already set the removed bit > in the css. If this is the case, however, this condition is impossible > and becomes useless - in which case you may want to remove it from Patch1. > Which I just saw you doing in patch5... =)
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