linux-kernel - [tip: sched/core] sched/uclamp: Fix initialization of struct uclamp

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Message-ID: <159428435710.4006.10577558696191415776.tip-bot2@tip-bot2>
Date:   Thu, 09 Jul 2020 08:45:57 -0000
From:   "tip-bot2 for Qais Yousef" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Qais Yousef <qais.yousef@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Lukasz Luba <lukasz.luba@....com>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/uclamp: Fix initialization of struct uclamp_rq

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     d81ae8aac85ca2e307d273f6dc7863a721bf054e
Gitweb:        https://git.kernel.org/tip/d81ae8aac85ca2e307d273f6dc7863a721bf054e
Author:        Qais Yousef <qais.yousef@....com>
AuthorDate:    Tue, 30 Jun 2020 12:21:22 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 08 Jul 2020 11:39:01 +02:00

sched/uclamp: Fix initialization of struct uclamp_rq

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@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@....com>
Tested-by: Lukasz Luba <lukasz.luba@....com>
Link: https://lkml.kernel.org/r/20200630112123.12076-2-qais.yousef@arm.com
---
 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 15c980a..9605db7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1239,6 +1239,20 @@ 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 = {};
@@ -1247,11 +1261,8 @@ 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],