On Wed, Jun 22, 2016 at 11:10:46AM +0300, Konstantin Khlebnikov wrote: > On 22.06.2016 00:10, Peter Zijlstra wrote: > >On Thu, Jun 16, 2016 at 03:57:01PM +0300, Konstantin Khlebnikov wrote: > >>Cgroup created inside throttled group must inherit current throttle_count. > >>Broken throttle_count allows to nominate throttled entries as a next buddy, > >>later this leads to null pointer dereference in pick_next_task_fair(). > >> > >>This patch initialize cfs_rq->throttle_count at first enqueue: laziness > >>allows to skip locking all rq at group creation. Lazy approach also allows > >>to skip full sub-tree scan at throttling hierarchy (not in this patch). > > > >You're talking about taking rq->lock in alloc_fair_sched_group(), right? > > > >We're about to go do that anyway... But I suppose for backports this > >makes sense. Doing it at creation time also avoids the issues Ben > >raised, right? > > Yes, all will be fine. But for 8192-cores this will be disaster =) Well, creating cgroups isn't something you do much of, and creating them will be proportionally expensive already, as we allocate all kinds of per-cpu data. In any case, we 'need' to do this because of the per entity load tracking stuff, entities, even blocked, should be added to the cfs_rq. > throttle_count must be initialized after linking tg into lists. obviously. Crud, that's later than we currently take the rq lock. Let me see how much pain it is to re-order all that. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html