Re: [PATCH 1/3] sched/core: Avoid requeueing a singleton balance callback

[Tejun Heo]

On Tue, Oct 20, 2026 at 10:43:19AM +0200, Andrea Righi wrote:
> With proxy execution, __schedule() can call set_next_task_scx() with
> SNT_REPICK and then SNT_PICK for the same donor. Both calls queue the
> kick_sync balance callback while kick_sync_pending remains set.
> 
> When the callback is the only list entry, its next pointer is NULL, so
> the existing duplicate check misses it. Queueing it again links it to
> itself and causes the wait to run twice.
> 
> Also check whether the callback is already the head of the list to
> reject the second insertion.
> 
> Fixes: e2859566ffbc ("sched_ext: Queue the kick_sync wait from set_next_task_scx()")
> Reported-by: Tejun Heo <tj@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/08cac02c604dd73ef96fc92eb29d692b@xxxxxxxxxx
> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>

Can you resend this to Peter? Please feel free to add

 Acked-by: Tejun Heo <tj@xxxxxxxxxx>

Thanks.

-- 
tejun