On Mon, 25 May 2020 at 16:42, gregkh@linuxfoundation.org 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@vger.kernel.org.

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@redhat.com 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@linaro.org Signed-off-by: Phil Auld pauld@redhat.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Link: https://lkml.kernel.org/r/20200512135222.GC2201@lorien.usersys.redhat.com

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: