sched_ext: Fix scx_kick_pseqs corruption on concurrent scheduler loads

If we load a BPF scheduler while another scheduler is already running,
alloc_kick_pseqs() would be called again, overwriting the previously
allocated arrays.

Fix by moving the alloc_kick_pseqs() call after the scx_enable_state()
check, ensuring that the arrays are only allocated when a scheduler can
actually be loaded.

Fixes: 14c1da3 ("sched_ext: Allocate scx_kick_cpus_pnt_seqs lazily using kvzalloc()")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: arighi

kernel/sched/ext.c

@@ -4577,15 +4577,15 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
 
 	mutex_lock(&scx_enable_mutex);
 
-	ret = alloc_kick_pseqs();
-	if (ret)
-		goto err_unlock;
-
 	if (scx_enable_state() != SCX_DISABLED) {
 		ret = -EBUSY;
-		goto err_free_pseqs;
+		goto err_unlock;
 	}
 
+	ret = alloc_kick_pseqs();
+	if (ret)
+		goto err_unlock;
+
 	sch = scx_alloc_and_add_sched(ops);
 	if (IS_ERR(sch)) {
 		ret = PTR_ERR(sch);