linux-kernel - [PATCH] sched:pelt: fix pelt clock sync when entering idle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260121163317.505635-1-vincent.guittot@linaro.org>
Date: Wed, 21 Jan 2026 17:33:17 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org,
	wusamuel@...gle.com,
	Alex.Hoh@...iatek.com,
	qyousef@...alina.io
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] sched:pelt: fix pelt clock sync when entering idle

Samuel and Alex reported regressions of the util_avg of RT rq with
commit 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection").
It happens that fair is updating and syncing the pelt clock with task one
when pick_next_task_fair() fails to pick a task but before the prev
scheduling class got a chance to update its pelt signals.

Move update_idle_rq_clock_pelt() in set_next_task_idle() which is called
after prev class has been called.

Fixes: 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection")
Reported-by: Samuel Wu <wusamuel@...gle.com>
Closes: https://lore.kernel.org/all/CAG2KctpO6VKS6GN4QWDji0t92_gNBJ7HjjXrE+6H+RwRXt=iLg@mail.gmail.com/
Tested-by: Samuel Wu <wusamuel@...gle.com>
Reported-by: Alex Hoh <Alex.Hoh@...iatek.com>
Closes: https://lore.kernel.org/all/8cf19bf0e0054dcfed70e9935029201694f1bb5a.camel@mediatek.com/
Tested-by: Alex Hoh <Alex.Hoh@...iatek.com>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 6 ------
 kernel/sched/idle.c | 6 ++++++
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 108213e94158..bea71564d3da 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8989,12 +8989,6 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 			goto again;
 	}
 
-	/*
-	 * rq is about to be idle, check if we need to update the
-	 * lost_idle_time of clock_pelt
-	 */
-	update_idle_rq_clock_pelt(rq);
-
 	return NULL;
 }
 
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 65eb8f8c1a5d..a7c5676b9abe 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -468,6 +468,12 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
 	scx_update_idle(rq, true, true);
 	schedstat_inc(rq->sched_goidle);
 	next->se.exec_start = rq_clock_task(rq);
+
+	/*
+	 * rq is about to be idle, check if we need to update the
+	 * lost_idle_time of clock_pelt
+	 */
+	update_idle_rq_clock_pelt(rq);
 }
 
 struct task_struct *pick_task_idle(struct rq *rq, struct rq_flags *rf)
-- 
2.43.0