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Date:   Thu, 16 Apr 2020 09:59:56 +0100
Message-Id: <20200416085956.217587-1-qperret@google.com>
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Subject: [PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp
From:   Quentin Perret <qperret@google.com>
To:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org
Cc:     dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, ctheegal@codeaurora.org, dianders@chromium.org,
        patrick.bellasi@matbug.net, valentin.schneider@arm.com,
        qais.yousef@arm.com, linux-kernel@vger.kernel.org,
        qperret@google.com, kernel-team@android.com
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Sender: linux-kernel-owner@vger.kernel.org
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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@codeaurora.org>
Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
Signed-off-by: Quentin Perret <qperret@google.com>
---
Changes in v2:
 - Added missing 'Fixes:' tag (Patrick)
 - Removed unnecessary local variable (Doug, Patrick)
---
 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 3a61a3b8eaa9..9a2fbf98fd6f 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);
 	}
 }
 
-- 
2.26.1.301.g55bc3eb7cb9-goog