[PATCH BUGFIX 1/1] sched_ext: Fix missing warning in scx_set_task_state() default case

[PATCH BUGFIX 1/1] sched_ext: Fix missing warning in scx_set_task_state() default case

[Samuele Mariotti]

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>
---
 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

Re: [PATCH BUGFIX 1/1] sched_ext: Fix missing warning in scx_set_task_state() default case

[Andrea Righi]

Hi Samuele,

On Thu, Apr 02, 2026 at 01:57:07PM +0200, Samuele Mariotti wrote:
> 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>

Nice catch, we should probably add:

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

With that:

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> ---
>  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
>