[PATCH] sched_ext: Fix stale errno in scx_sub_enable_workfn()

[Cui Jian]

scx_sub_enable_workfn() drops the return value of validate_ops().
When validate_ops() fails, the function jumps to err_disable with
ret still holding 0 from the previous call, so the fallback error
added by commit db4e9defd2e8 ("sched_ext: Record an error on
errno-only sub-enable failure") reports "scx_sub_enable() failed
(0)".

This is currently harmless because validate_ops() records its own
scx_error() first and the first error wins, but it leaves the
fallback broken for this path. Save the return value into ret,
like scx_root_enable_workfn() already does.

The nesting depth check and the cgroup online check also reach
err_disable without setting ret. Set -EINVAL and -ENODEV there so
the fallback always reports a real errno.

Signed-off-by: Cui Jian <cjian720@xxxxxxx>
---
 kernel/sched/ext/ext.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index e3fa7b2fac9d..e623d6375f66 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -7559,6 +7559,7 @@ static void scx_sub_enable_workfn(struct kthread_work *work)
 	if (sch->level >= SCX_SUB_MAX_DEPTH) {
 		scx_error(sch, "max nesting depth %d violated",
 			  SCX_SUB_MAX_DEPTH);
+		ret = -EINVAL;
 		goto err_disable;
 	}
 
@@ -7580,7 +7581,8 @@ static void scx_sub_enable_workfn(struct kthread_work *work)
 	if (ret)
 		goto err_disable;
 
-	if (validate_ops(sch, ops))
+	ret = validate_ops(sch, ops);
+	if (ret)
 		goto err_disable;
 
 	struct scx_sub_attach_args sub_attach_args = {
@@ -7613,6 +7615,7 @@ static void scx_sub_enable_workfn(struct kthread_work *work)
 	set_cgroup_sched(sch_cgroup(sch), sch);
 	if (!(cgrp->self.flags & CSS_ONLINE)) {
 		scx_error(sch, "cgroup is not online");
+		ret = -ENODEV;
 		goto err_unlock_and_disable;
 	}
 

base-commit: 1229e2e57a5c2980ccd457b9b53ea0eed5a22ab3
-- 
2.34.1