On Thu, Dec 16, 2010 at 4:54 PM, Paul Menage <menage@xxxxxxxxxx> wrote: > On Thu, Dec 2, 2010 at 7:07 PM, Colin Cross <ccross@xxxxxxxxxxx> wrote: >>> 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. > > I don't quite follow your argument here. Are you saying that the > problem is that you could end up spawning a release agent for a cgroup > that was no longer releasable since it now had a process in it again? > If so, then I don't think that's a problem - spurious release agent > invocations for non-empty cgroups will always happen occasionally due > to races between the kernel and userspace. But a failed move of a task > into a previously-empty cgroup shouldn't trigger the agent. No, if you add a new process to the group while check_for_release, the bit could get set by the add for the new process, then cleared by the concurrently running check_for_release. The release agent would be spawned with a process in the group, which is fine, but when RELEASABLE bit would be clear. When the new process was removed, check_for_release would not call the release agent at all. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
