linux-kernel - Re: [PATCH v3] sched/fair: Fix enqueue_task

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Message-ID: <20200512141048.GL2978@hirez.programming.kicks-ass.net>
Date:   Tue, 12 May 2020 16:10:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Phil Auld <pauld@...hat.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        vincent.guittot@...aro.org, juri.lelli@...hat.com,
        zohooouoto@...o.com.cn, dietmar.eggemann@....com
Subject: Re: [PATCH v3] sched/fair: Fix enqueue_task_fair warning some more

On Tue, May 12, 2020 at 09:52:22AM -0400, Phil Auld wrote:
> sched/fair: Fix enqueue_task_fair warning some more
> 
> The recent patch, fe61468b2cb (sched/fair: Fix enqueue_task_fair warning)
> did not fully resolve the issues with the rq->tmp_alone_branch !=
> &rq->leaf_cfs_rq_list warning in enqueue_task_fair. There is a case where
> the first for_each_sched_entity loop exits due to on_rq, having incompletely
> updated the list.  In this case the second for_each_sched_entity loop can
> further modify se. The later code to fix up the list management fails to do
> what is needed because se does not point to the sched_entity which broke out
> of the first loop. The list is not fixed up because the throttled parent was
> already added back to the list by a task enqueue in a parallel child hierarchy.
> 
> Address this by calling list_add_leaf_cfs_rq if there are throttled parents
> while doing the second for_each_sched_entity loop.
> 
> v3: clean up commit message and add fixes and review tags.

Excellent, ignore what I just sent, I now have this one.