Commit 315c4f884800 for kernel

commit 315c4f884800c45cb6bd8c90422fad554a8b9588
Author: Qais Yousef <>
Date:   Thu Dec 2 11:20:33 2021 +0000

    sched/uclamp: Fix rq->uclamp_max not set on first enqueue

    Commit d81ae8aac85c ("sched/uclamp: Fix initialization of struct
    uclamp_rq") introduced a bug where uclamp_max of the rq is not reset to
    match the woken up task's uclamp_max when the rq is idle.

    The code was relying on rq->uclamp_max initialized to zero, so on first

            static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
                                                enum uclamp_id clamp_id)

                    if (uc_se->value > READ_ONCE(uc_rq->value))
                            WRITE_ONCE(uc_rq->value, uc_se->value);

    was actually resetting it. But since commit d81ae8aac85c changed the
    default to 1024, this no longer works. And since rq->uclamp_flags is
    also initialized to 0, neither above code path nor uclamp_idle_reset()
    update the rq->uclamp_max on first wake up from idle.

    This is only visible from first wake up(s) until the first dequeue to
    idle after enabling the static key. And it only matters if the
    uclamp_max of this task is < 1024 since only then its uclamp_max will be
    effectively ignored.

    Fix it by properly initializing rq->uclamp_flags = UCLAMP_FLAG_IDLE to
    ensure uclamp_idle_reset() is called which then will update the rq
    uclamp_max value as expected.

    Fixes: d81ae8aac85c ("sched/uclamp: Fix initialization of struct uclamp_rq")
    Signed-off-by: Qais Yousef <>
    Signed-off-by: Peter Zijlstra (Intel) <>
    Reviewed-by: Valentin Schneider <>
    Tested-by: Dietmar Eggemann <>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 814c52d90c0f..77563109c0ea 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1918,7 +1918,7 @@ static void __init init_uclamp_rq(struct rq *rq)

-	rq->uclamp_flags = 0;
+	rq->uclamp_flags = UCLAMP_FLAG_IDLE;

 static void __init init_uclamp(void)