On Fri, Apr 13, 2012 at 02:38:52PM -0700, Tejun Heo wrote: > On Fri, Apr 13, 2012 at 05:33:44PM -0400, Vivek Goyal wrote: > > On Fri, Apr 13, 2012 at 02:05:48PM -0700, Tejun Heo wrote: > > > On Fri, Apr 13, 2012 at 04:55:01PM -0400, Vivek Goyal wrote: > > > > But neither seems to be the case here. So to make sure that blkg_lookup() > > > > under rcu will see the updated value of queue flag (bypass), are we > > > > relying on the fact that caller should see the DEAD flag and not go > > > > ahead with blkg_lookup()? If yes, atleast it is not obivious. > > > > > > We're relying on the fact that it doesn't matter anymore because all > > > blkgs will be shoot down in queue cleanup path which goes through rcu > > > free, which is different from deactivating individual policies. It > > > indeed is subtle. Umm... this is starting to get ridiculous. Why the > > > hell was megaraid messing with so many queues anyways? > > > > Well, blkcg_deactivate_policy() frees the policy data in a non-rcu > > manner. So group is around but policy data is gone. So technically if some > > IO submitter does not see the queue bypass flag, he might still try to > > access blkg->pd[pol->plid] after being freed. > > No, we always go through blkg_destroy_all() and each blkg along with > any attached policy_data will go through RCU grace period before > getting destroyed. It is stupid subtle but nevertheless correct. Ok, I see that we are calling blkg_destroy_all() before we call blk_throtl_exit() or elevator_exit(). So yes, this should be fine. Thanks Vivek _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
