Commit eaf5a92e authored Apr 16, 2020 by Quentin Perret Committed by Peter Zijlstra Apr 22, 2020

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: 1a00d999 ("sched/uclamp: Set default clamps for RT tasks")
Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20200416085956.217587-1-qperret@google.com

parent db441bd9

kernel/sched/core.c

+2 −7

Original line number	Diff line number	Diff line
		@@ -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);
		}
		}

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