On 24/07/09 14:57 -0700, Paul Menage wrote: > 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. css_set sharing is the bit I was missing. Thanks! Louis -- Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes
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