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    Subject[PATCH 5.6 126/126] sched/fair: Fix enqueue_task_fair() warning some more
    Date
    From: Phil Auld <pauld@redhat.com>

    [ Upstream commit b34cb07dde7c2346dec73d053ce926aeaa087303 ]

    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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/sched/fair.c | 7 +++++++
    1 file changed, 7 insertions(+)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 7cd86641b44b..603d3d3cbf77 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -5298,6 +5298,13 @@ 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:
    --
    2.25.1


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