linux-kernel - [PATCH] sched/uclamp: Fix rq->uclamp

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Message-Id: <20211125165233.1425633-1-qais.yousef@arm.com>
Date:   Thu, 25 Nov 2021 16:52:33 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org, Qais Yousef <qais.yousef@....com>
Subject: [PATCH] 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. This only
impacts the first wake up 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 we reset rq uclamp_max when waking up from idle.

Fixes: d81ae8aac85c ("sched/uclamp: Fix initialization of struct uclamp_rq")
Signed-off-by: Qais Yousef <qais.yousef@....com>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index beaa8be6241e..52b0c7513a32 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1929,7 +1929,7 @@ 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)
-- 
2.25.1