On Mon, 25 May 2020 at 16:42, <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
>
> The patch below does not apply to the 5.6-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
This patch applies on top of
commit 6d4d22468dae ("sched/fair: Reorder enqueue/dequeue_task_fair path")
commit 5ab297bab984 ("sched/fair: Fix reordering of
enqueue/dequeue_task_fair()")
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From b34cb07dde7c2346dec73d053ce926aeaa087303 Mon Sep 17 00:00:00 2001
> From: Phil Auld <pauld@xxxxxxxxxx>
> Date: Tue, 12 May 2020 09:52:22 -0400
> Subject: [PATCH] sched/fair: Fix enqueue_task_fair() warning some more
>
> 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.
>
> Fixes: fe61468b2cb ("sched/fair: Fix enqueue_task_fair warning")
> Suggested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Signed-off-by: Phil Auld <pauld@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Link: https://lkml.kernel.org/r/20200512135222.GC2201@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 02f323b85b6d..c6d57c334d51 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5479,6 +5479,13 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> /* end evaluation on encountering a throttled cfs_rq */
> if (cfs_rq_throttled(cfs_rq))
> goto enqueue_throttle;
> +
> + /*
> + * One parent has been throttled and cfs_rq removed from the
> + * list. Add it back to not break the leaf list.
> + */
> + if (throttled_hierarchy(cfs_rq))
> + list_add_leaf_cfs_rq(cfs_rq);
> }
>
> enqueue_throttle:
>
