linux-kernel - [PATCH] sched_ext: Fix rq lock state in hotplug ops

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Message-ID: <20250428214320.137576-1-arighi@nvidia.com>
Date: Mon, 28 Apr 2025 23:43:20 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] sched_ext: Fix rq lock state in hotplug ops

The ops.cpu_online() and ops.cpu_offline() callbacks incorrectly assume
that the rq involved in the operation is locked, which is not the case
during hotplug, triggering the following warning:

  WARNING: CPU: 1 PID: 20 at kernel/sched/sched.h:1504 handle_hotplug+0x280/0x340

Fix by not tracking the target rq as locked in the context of
ops.cpu_online() and ops.cpu_offline().

Fixes: 18853ba782bef ("sched_ext: Track currently locked rq")
Reported-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/ext.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index ac79067dc87e6..d0f40fd258752 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3477,9 +3477,9 @@ static void handle_hotplug(struct rq *rq, bool online)
 		scx_idle_update_selcpu_topology(&scx_ops);
 
 	if (online && SCX_HAS_OP(cpu_online))
-		SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_online, rq, cpu);
+		SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_online, NULL, cpu);
 	else if (!online && SCX_HAS_OP(cpu_offline))
-		SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_offline, rq, cpu);
+		SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_offline, NULL, cpu);
 	else
 		scx_ops_exit(SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
 			     "cpu %d going %s, exiting scheduler", cpu,
-- 
2.49.0