[PATCH BUGFIX] sched_ext: Fix missing warning in scx_set_task_state() default case

Samuele Mariotti
2026-04-02T17:00:57Z

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.

Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class")

Signed-off-by: Samuele Mariotti <smariotti@disroot.org>
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
---
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 1594987d637b..10683ce4e415 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2863,7 +2863,8 @@ 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;
}

--
2.47.3