On Wed, Nov 24, 2010 at 4:21 PM, Paul Menage <menage@xxxxxxxxxx> wrote: > On Wed, Nov 24, 2010 at 4:11 PM, Colin Cross <ccross@xxxxxxxxxxx> wrote: >>> >>> We seem to have lost some notify_on_release() checks - maybe move that >>> to check_for_release()? >> check_for_release immediately calls cgroup_is_releasable, which checks >> for the same bit as notify_on_release. There's no need for >> CGRP_RELEASABLE to depend on notify_on_release, or to check >> notify_on_release before calling check_for_release. > > OK. > >> I matched the existing behavior, __css_put sets CGRP_RELEASABLE when >> refcnt goes to 0. >> > > Ah, we do appear to have had that behaviour for a while. I don't > remember the justification for it at this point :-) > >> check_for_release is only called from __css_put, cgroup_rmdir, and >> __put_css_set (or free_css_set_work after my second patch). Those all >> imply that __css_get, get_css_set, or cgroup_create have been >> previously called, which are the functions that set CGRP_RELEASABLE. > > Not in one case - if we create a new cgroup and try to move a thread > into it, but the thread is exiting as we move it, we'll call > put_css_set() on the new css_set, which will drop the refcount on the > target cgroup back to 0. We wouldn't want the auto-release > notification to kick in in that situation, I think. Clearing the CGRP_RELEASABLE bit any time after the tests in check_for_release introduces a race if __css_get is called between the check and clearing the bit - the cgroup will have an entry, but the bit will not be set. Without additional locking in __css_get, I don't see any way to safely clear CGRP_RELEASABLE. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
