Quoting Serge E. Hallyn (serue@xxxxxxxxxx): > Quoting Benjamin Blum (bblum@xxxxxxxxxx): > > On Mon, Aug 3, 2009 at 1:54 PM, Serge E. Hallyn<serue@xxxxxxxxxx> wrote: > > > Quoting Ben Blum (bblum@xxxxxxxxxx): > > > What *exactly* is it we are protecting with cgroup_fork_mutex? > > > 'fork' (as the name implies) is not a good answer, since we should be > > > protecting data, not code. If it is solely tsk->cgroups, then perhaps > > > we should in fact try switching to (s?)rcu. Then cgroup_fork() could > > > just do rcu_read_lock, while cgroup_task_migrate() would make the change > > > under a spinlock (to protect against concurrent cgroup_task_migrate()s), > > > and using rcu_assign_pointer to let cgroup_fork() see consistent data > > > either before or after the update... That might mean that any checks done > > > before completing the migrate which involve the # of tasks might become > > > invalidated before the migration completes? Seems acceptable (since > > > it'll be a small overcharge at most and can be quickly remedied). > > > > You'll notice where the rwsem is released - not until cgroup_post_fork > > or cgroup_fork_failed. It doesn't just protect the tsk->cgroups > > pointer, but rather guarantees atomicity between adjusting > > tsk->cgroups and attaching it to the cgroups lists with respect to the > > critical section in attach_proc. If you've a better name for the lock > > for such a race condition, do suggest. > > No the name is pretty accurate - it's the lock itself I'm objecting > to. Maybe it's the best we can do, though. This is probably a stupid idea, but... what about having zero overhead at clone(), and instead, at cgroup_task_migrate(), dequeue_task()ing all of the affected threads for the duration of the migrate? /me prepares to be hit by blunt objects -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
