linux-kernel - [PATCH] sched_ext: idle: Fix return code of scx_select_cpu

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Message-ID: <20250326191849.195303-1-arighi@nvidia.com>
Date: Wed, 26 Mar 2025 20:18:49 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched_ext: idle: Fix return code of scx_select_cpu_dfl()

Return -EBUSY when using %SCX_PICK_IDLE_CORE with scx_select_cpu_dfl()
if a fully idle SMT core cannot be found, instead of falling back to
@prev_cpu, which is not a fully idle SMT core in this case.

Fixes: c414c2171cd9e ("sched_ext: idle: Honor idle flags in the built-in idle selection policy")
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/ext_idle.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 52c36a70a3d04..45061b5843806 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -544,7 +544,7 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, u64
 		 * core.
 		 */
 		if (flags & SCX_PICK_IDLE_CORE) {
-			cpu = prev_cpu;
+			cpu = -EBUSY;
 			goto out_unlock;
 		}
 	}
-- 
2.49.0