linux-kernel - [PATCH 1/2] sched/uclamp: Fix initialization of strut uclamp

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Message-Id: <20200618195525.7889-2-qais.yousef@arm.com>
Date:   Thu, 18 Jun 2020 20:55:24 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Qais Yousef <qais.yousef@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Chris Redpath <chrid.redpath@....com>,
        Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] sched/uclamp: Fix initialization of strut 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>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
CC: Patrick Bellasi <patrick.bellasi@...bug.net>
Cc: Chris Redpath <chrid.redpath@....com>
Cc: Lukasz Luba <lukasz.luba@....com>
Cc: linux-kernel@...r.kernel.org
---
 kernel/sched/core.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a43c84c27c6f..e19d2b915406 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1248,6 +1248,20 @@ 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) {
+		memset(uc_rq[clamp_id].bucket,
+		       0,
+		       sizeof(struct uclamp_bucket)*UCLAMP_BUCKETS);
+
+		uc_rq[clamp_id].value = uclamp_none(clamp_id);
+	}
+}
+
 static void __init init_uclamp(void)
 {
 	struct uclamp_se uc_max = {};
@@ -1257,8 +1271,7 @@ 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);
+		init_uclamp_rq(cpu_rq(cpu));
 		cpu_rq(cpu)->uclamp_flags = 0;
 	}
 
-- 
2.17.1