[PATCH 6.18.y 1/2] sched_ext: Fix missing warning in scx_set_task_state() default case

[Sasha Levin <sashal@kernel.org>]

From: Samuele Mariotti <smariotti@disroot.org>

[ Upstream commit b905ee77d5f557a83a485b4146210f54f13365fc ]

In scx_set_task_state(), the default case was setting the
warn flag, but then returning immediately. This is problematic
because the only purpose of the warn flag is to trigger
WARN_ONCE, but the early return prevented it from ever firing,
leaving invalid task states undetected and untraced.

To fix this, a WARN_ONCE call is now added directly in the
default case.

The fix addresses two aspects:

 - Guarantees the invalid task states are properly logged
   and traced.

 - Provides a distinct warning message
   ("sched_ext: Invalid task state") specifically for
   states outside the defined scx_task_state enum values,
   making it easier to distinguish from other transition
   warnings.

This ensures proper detection and reporting of invalid states.

Signed-off-by: Samuele Mariotti <smariotti@disroot.org>
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Stable-dep-of: 9a415cc53711 ("sched_ext: Avoid UAF in scx_root_enable_workfn() init failure path")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/sched/ext.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 177bbf31116d0..54621f6226886 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2800,7 +2800,8 @@ static void scx_set_task_state(struct task_struct *p, enum scx_task_state state)
 		warn = prev_state != SCX_TASK_READY;
 		break;
 	default:
-		warn = true;
+		WARN_ONCE(1, "sched_ext: Invalid task state %d -> %d for %s[%d]",
+			  prev_state, state, p->comm, p->pid);
 		return;
 	}
 
-- 
2.53.0