linux-kernel - [PATCH 07/17] sched/core: Set balance

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Message-ID: <20251204175405.1511340-8-srikar@linux.ibm.com>
Date: Thu,  4 Dec 2025 23:23:55 +0530
From: Srikar Dronamraju <srikar@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Peter Zijlstra <peterz@...radead.org>
Cc: Ben Segall <bsegall@...gle.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mel Gorman <mgorman@...e.de>, Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Shrikanth Hegde <sshegde@...ux.ibm.com>,
        Srikar Dronamraju <srikar@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Swapnil Sapkal <swapnil.sapkal@....com>,
        Thomas Huth <thuth@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        virtualization@...ts.linux.dev, Yicong Yang <yangyicong@...ilicon.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH 07/17] sched/core: Set balance_callback only if CPU is dying

Scheduler is suppose to set balance_callback to push tasks out of a
dying CPU. However the current code, unilaterally sets the balance_cpu
and then checks if the CPU is indeed dying.

Remove this anomaly by setting balance_callback only after checking if
the CPU is about to die.

Signed-off-by: Srikar Dronamraju <srikar@...ux.ibm.com>
---
 kernel/sched/core.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f754a60de848..89efff1e1ead 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8173,11 +8173,6 @@ static void balance_push(struct rq *rq)
 
 	lockdep_assert_rq_held(rq);
 
-	/*
-	 * Ensure the thing is persistent until balance_push_set(.on = false);
-	 */
-	rq->balance_callback = &balance_push_callback;
-
 	/*
 	 * Only active while going offline and when invoked on the outgoing
 	 * CPU.
@@ -8185,6 +8180,11 @@ static void balance_push(struct rq *rq)
 	if (!cpu_dying(rq->cpu) || rq != this_rq())
 		return;
 
+	/*
+	 * Ensure the thing is persistent until balance_push_set(.on = false);
+	 */
+	rq->balance_callback = &balance_push_callback;
+
 	/*
 	 * Both the cpu-hotplug and stop task are in this case and are
 	 * required to complete the hotplug process.
-- 
2.43.7