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Date: Thu, 4 May 2017 13:31:38 -0400
From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
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Subject: Re: [PATCH 1/2] sched/fair: Use task_groups instead of
 leaf_cfs_rq_list to walk all cfs_rqs
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Hello, Peter.

On Thu, May 04, 2017 at 03:31:22PM +0200, Peter Zijlstra wrote:
> Yes we can hit an (almost) dead cfs_rq, but poking the bandwidth
> variables thereof is harmless.
> 
> unthrottle_cfs_rq() also stops doing anything much when it finds the
> cfs_rq is empty, which must be the case if we're removing it.

Yeah, if you're okay with calling the functions on dead cfs_rq's, just
wrapping with rcu_read_lock should be enough.

> I don't know Paul's opinion on RCU GPs happening while stop_machine(),
> but just in case he feels that's fair game, I did add the
> rcu_read_lock() thingies.
> 
> The lockdep assert is mostly documentation, to more easily see
> it is indeed held when we get there.
> 
> I left print_cfs_stats using the leaf list, no point in printing stuff
> that's empty.
> 
> This way we can avoid taking all RQ locks on cgroup destruction.

Looks good to me.

Thanks.

-- 
tejun