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    Subject[PATCH AUTOSEL 5.8 25/72] sched/uclamp: Fix initialization of struct uclamp_rq
    Date
    From: Qais Yousef <qais.yousef@arm.com>

    [ Upstream commit d81ae8aac85ca2e307d273f6dc7863a721bf054e ]

    struct uclamp_rq was zeroed out entirely in assumption that in the first
    call to uclamp_rq_inc() they'd be initialized correctly in accordance to
    default settings.

    But when next patch introduces a static key to skip
    uclamp_rq_{inc,dec}() until userspace opts in to use uclamp, schedutil
    will fail to perform any frequency changes because the
    rq->uclamp[UCLAMP_MAX].value is zeroed at init and stays as such. Which
    means all rqs are capped to 0 by default.

    Fix it by making sure we do proper initialization at init without
    relying on uclamp_rq_inc() doing it later.

    Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
    Signed-off-by: Qais Yousef <qais.yousef@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
    Tested-by: Lukasz Luba <lukasz.luba@arm.com>
    Link: https://lkml.kernel.org/r/20200630112123.12076-2-qais.yousef@arm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/sched/core.c | 21 ++++++++++++++++-----
    1 file changed, 16 insertions(+), 5 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 2142c67676826..c3cbdc436e2e4 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -1237,6 +1237,20 @@ static void uclamp_fork(struct task_struct *p)
    }
    }

    +static void __init init_uclamp_rq(struct rq *rq)
    +{
    + enum uclamp_id clamp_id;
    + struct uclamp_rq *uc_rq = rq->uclamp;
    +
    + for_each_clamp_id(clamp_id) {
    + uc_rq[clamp_id] = (struct uclamp_rq) {
    + .value = uclamp_none(clamp_id)
    + };
    + }
    +
    + rq->uclamp_flags = 0;
    +}
    +
    static void __init init_uclamp(void)
    {
    struct uclamp_se uc_max = {};
    @@ -1245,11 +1259,8 @@ static void __init init_uclamp(void)

    mutex_init(&uclamp_mutex);

    - for_each_possible_cpu(cpu) {
    - memset(&cpu_rq(cpu)->uclamp, 0,
    - sizeof(struct uclamp_rq)*UCLAMP_CNT);
    - cpu_rq(cpu)->uclamp_flags = 0;
    - }
    + for_each_possible_cpu(cpu)
    + init_uclamp_rq(cpu_rq(cpu));

    for_each_clamp_id(clamp_id) {
    uclamp_se_set(&init_task.uclamp_req[clamp_id],
    --
    2.25.1
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