On Tue, Aug 16, 2011 at 12:50:06AM +0200, Frederic Weisbecker wrote: > On Mon, Aug 15, 2011 at 08:49:57PM +0200, Oleg Nesterov wrote: > > On 07/29, Ben Blum wrote: > > > > > > According to this thread - https://lkml.org/lkml/2011/7/27/243 - RCU is > > > not sufficient to guarantee the tasklist is stable w.r.t. de_thread and > > > exit. Taking tasklist_lock for reading, instead of rcu_read_lock, > > > ensures proper exclusion. > > > > Yes. > > > > So far I still think we should fix while_each_thread() so that it works > > under rcu_read_lock() "as exepected", I'll try to think more. > > > > But whatever we do with while_each_thread(), this can't help > > cgroup_attach_proc(), it needs the locking. > > > > > - rcu_read_lock(); > > > + read_lock(&tasklist_lock); > > > if (!thread_group_leader(leader)) { > > > > Agreed, this should work. > > > > But can't we avoid the global list? thread_group_leader() or not, we do > > not really care. We only need to ensure we can safely find all threads. > > > > How about the patch below? > > > > > > With or without this/your patch this leader can die right after we > > drop the lock. ss->can_attach(leader) and ss->attach(leader) look > > suspicious. If a sub-thread execs, this task_struct has nothing to > > do with the threadgroup. > > > > > > > > Also. This is off-topic, but... Why cgroup_attach_proc() and > > cgroup_attach_task() do ->attach_task() + cgroup_task_migrate() > > in the different order? cgroup_attach_proc() looks wrong even > > if currently doesn't matter. > > Right. As we concluded in our off-list discussion, if there > is no strong reason for that, I'm going to fix that in my task > counter patchset because there it really matters. If we can't > migrate the thread because it has already exited, we really > don't want to call ->attach_task() but rather cancel_attach_task(). > > Thanks. > Yes. Um, this must have been a mistake on my part. The lines of code should be the other way around. It should be done in a separate bugfix patch, though, so it goes through faster... -- Ben _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
