On Fri, Jul 24, 2009 at 2:52 PM, Benjamin Blum<bblum@xxxxxxxxxx> wrote: >> I don't see how css_sets are guaranteed while cgroup_fork_mutex is not held and >> thus does not prevent new threads from being created right now. Could you >> elaborate on that? > > Prefetching the css sets is independent of the fork lock/race issue. > The idea is that we build a list, kept locally, that has references on > all the css_sets we'll need to migrate each thread to the new cgroup. > Since ordinarily we might need to malloc a new css_set for a thread > before moving it, and it's possible that that could fail, we need to > do allocations for all threads to be moved before committing any of > them. As long as we have the list of prefetched css_sets, they'll stay > there, and at the end, we drop the extra references we took on them to > make that guarantee when tearing down the list. And more specifically, since only the holder of cgroup_mutex can move a thread to a new cgroup (and hence a potentially new unique css_set), we know that once we've run through all the threads in the thread_group and verified that we have the appropriate pre-fetched css_set objects for all of them, it doesn't matter if any new threads are created - they'll share one of the pre-fetched css_sets. Paul _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
