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    Subject[PATCH 5.4 41/83] sched/core: Fix reset-on-fork from RT with uclamp
    Date
    From: Quentin Perret <qperret@google.com>

    commit eaf5a92ebde5bca3bb2565616115bd6d579486cd upstream.

    uclamp_fork() resets the uclamp values to their default when the
    reset-on-fork flag is set. It also checks whether the task has a RT
    policy, and sets its uclamp.min to 1024 accordingly. However, during
    reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
    hence leading to an erroneous uclamp.min setting for the new task if it
    was forked from RT.

    Fix this by removing the unnecessary check on rt_task() in
    uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
    set.

    Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
    Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
    Signed-off-by: Quentin Perret <qperret@google.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
    Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
    Link: https://lkml.kernel.org/r/20200416085956.217587-1-qperret@google.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/sched/core.c | 9 ++-------
    1 file changed, 2 insertions(+), 7 deletions(-)

    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -1233,13 +1233,8 @@ static void uclamp_fork(struct task_stru
    return;

    for_each_clamp_id(clamp_id) {
    - unsigned int clamp_value = uclamp_none(clamp_id);
    -
    - /* By default, RT tasks always get 100% boost */
    - if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
    - clamp_value = uclamp_none(UCLAMP_MAX);
    -
    - uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
    + uclamp_se_set(&p->uclamp_req[clamp_id],
    + uclamp_none(clamp_id), false);
    }
    }


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