linux-kernel - [RFC PATCH 12/19] sched/fair: Reorder the barrier in nohz_balance_enter

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

Message-ID: <20250904041516.3046-13-kprateek.nayak@amd.com>
Date: Thu, 4 Sep 2025 04:15:08 +0000
From: K Prateek Nayak <kprateek.nayak@....com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner
	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
CC: Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
	<rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman
	<mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, K Prateek Nayak
	<kprateek.nayak@....com>, "Gautham R. Shenoy" <gautham.shenoy@....com>,
	Swapnil Sapkal <swapnil.sapkal@....com>
Subject: [RFC PATCH 12/19] sched/fair: Reorder the barrier in nohz_balance_enter_idle()

The smp_mb__after_atomic() in nohz_balance_enter_idle() is used to order
the setting of the nohz idle CPU on the "nohz.idle_cpus_mask" with the
write to "nohz.needs_update" as per the comment.

Since set_cpu_sd_state_idle() is now responsible for idle tracking using
"sd_nohz->shared", reorder the call to set_cpu_sd_state_idle() to come
before the barrier ensuring the CPU is tracked on the idle mask before
the update to "nohz.needs_update" is observed.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8226520758d..d13de6feb467 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12544,6 +12544,8 @@ void nohz_balance_enter_idle(int cpu)
 	cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
 	atomic_inc(&nohz.nr_cpus);
 
+	set_cpu_sd_state_idle(cpu);
+
 	/*
 	 * Ensures that if nohz_idle_balance() fails to observe our
 	 * @idle_cpus_mask store, it must observe the @has_blocked
@@ -12551,8 +12553,6 @@ void nohz_balance_enter_idle(int cpu)
 	 */
 	smp_mb__after_atomic();
 
-	set_cpu_sd_state_idle(cpu);
-
 	WRITE_ONCE(nohz.needs_update, 1);
 out:
 	/*
-- 
2.34.1