linux-kernel - [tip: sched/urgent] sched/core: Fix reset-on-fork from RT with uclamp

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Message-ID: <158759044717.28353.7054325009828879499.tip-bot2@tip-bot2>
Date:   Wed, 22 Apr 2020 21:20:47 -0000
From:   "tip-bot2 for Quentin Perret" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Chitti Babu Theegala <ctheegal@...eaurora.org>,
        Quentin Perret <qperret@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/urgent] sched/core: Fix reset-on-fork from RT with uclamp

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

Commit-ID:     eaf5a92ebde5bca3bb2565616115bd6d579486cd
Gitweb:        https://git.kernel.org/tip/eaf5a92ebde5bca3bb2565616115bd6d579486cd
Author:        Quentin Perret <qperret@...gle.com>
AuthorDate:    Thu, 16 Apr 2020 09:59:56 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 22 Apr 2020 23:10:13 +02:00

sched/core: Fix reset-on-fork from RT with uclamp

uclamp_fork() resets the uclamp values to their default when the
reset-on-fork flag is set. It also checks whether the task has a RT
policy, and sets its uclamp.min to 1024 accordingly. However, during
reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
hence leading to an erroneous uclamp.min setting for the new task if it
was forked from RT.

Fix this by removing the unnecessary check on rt_task() in
uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
set.

Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
Reported-by: Chitti Babu Theegala <ctheegal@...eaurora.org>
Signed-off-by: Quentin Perret <qperret@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Patrick Bellasi <patrick.bellasi@...bug.net>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Link: https://lkml.kernel.org/r/20200416085956.217587-1-qperret@google.com
---
 kernel/sched/core.c |  9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3a61a3b..9a2fbf9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
 		return;
 
 	for_each_clamp_id(clamp_id) {
-		unsigned int clamp_value = uclamp_none(clamp_id);
-
-		/* By default, RT tasks always get 100% boost */
-		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
-			clamp_value = uclamp_none(UCLAMP_MAX);
-
-		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
+		uclamp_se_set(&p->uclamp_req[clamp_id],
+			      uclamp_none(clamp_id), false);
 	}
 }