Messages in this thread | | | From | Mathias Krause <> | Subject | Re: [PATCH] sched/fair: Prevent dead task groups from regaining cfs_rq's | Date | Thu, 4 Nov 2021 18:37:50 +0100 |
| |
Am 04.11.21 um 17:49 schrieb Vincent Guittot: > [snip] > > Ok so we must have 2 GPs: > > list_del_rcu(&tg->siblings); > GP to wait for the end of ongoing walk_tg_tree_from : synchronize_rcu > in your patch > list_del_leaf_cfs_rq(tg->cfs_rq[cpu]); if on_list > remove_entity_load_avg(tg->se[cpu]); > GP to wait for the end of ongoing for_each_leaf_cfs_rq_safe (print_cfs_stats) > kfree everything
Basically yes, but with my patch we already have these two, as there's at least one RCU GP between after sched_offline_group() finishes and sched_free_group() / cpu_cgroup_css_free() starts.
So we either use my patch as-is or move unregister_fair_sched_group() to free_fair_sched_group() and use kfree_rcu() instead of kfree(). Both approaches have pros and cons.
Pro for my version is the early unlinking of cfs_rq's for dead task groups, so no surprises later on. Con is the explicit synchronize_rcu().
Pro for the kfree_rcu() approach is the lack of the explicit synchronize_rcu() call, so no explicit blocking operation. Con is that we have cfs_rq's re-added to dead task groups which feels wrong and need to find a suitable member to overlap with the rcu_head in each involved data type.
Which one do you prefer?
Thanks, Mathias
| |