From: Andrea Righi <arighi@nvidia.com>
Date: Thu, 4 Sep 2025 05:57:16 +0000 (+0200)
Subject: sched_ext: Exit early on hotplug events during attach
X-Git-Tag: v6.19-rc1~177^2~47
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0128c850513a7f5199397a79da9c39558a5558cb;p=thirdparty%2Fkernel%2Flinux.git

sched_ext: Exit early on hotplug events during attach

There is no need to complete the entire scx initialization if a
scheduler is failing to be attached due to a hotplug event.

Exit early to avoid unnecessary work and simplify the attach flow.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index c645d47124e72..9b2ab67951e68 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4513,7 +4513,7 @@ err_free_sch:
 	return ERR_PTR(ret);
 }
 
-static void check_hotplug_seq(struct scx_sched *sch,
+static int check_hotplug_seq(struct scx_sched *sch,
 			      const struct sched_ext_ops *ops)
 {
 	unsigned long long global_hotplug_seq;
@@ -4530,8 +4530,11 @@ static void check_hotplug_seq(struct scx_sched *sch,
 				 SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
 				 "expected hotplug seq %llu did not match actual %llu",
 				 ops->hotplug_seq, global_hotplug_seq);
+			return -EBUSY;
 		}
 	}
+
+	return 0;
 }
 
 static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
@@ -4633,7 +4636,11 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
 		if (((void (**)(void))ops)[i])
 			set_bit(i, sch->has_op);
 
-	check_hotplug_seq(sch, ops);
+	ret = check_hotplug_seq(sch, ops);
+	if (ret) {
+		cpus_read_unlock();
+		goto err_disable;
+	}
 	scx_idle_update_selcpu_topology(ops);
 
 	cpus_read_unlock();