Re: [PATCH sched/urgent] sched/deadline: Fix stale rq->dl_server after a server pick returns RETRY_TASK

[Tejun Heo]

On Fri, Oct 30, 2026 at 12:18:42PM -1000, Tejun Heo wrote:
> __pick_task_dl() records the server in rq->dl_server whenever the server's
> pick returns non-NULL, RETRY_TASK included. __pick_next_task() clears
> rq->dl_server at its top, but a RETRY_TASK restarts the pick below that
> clear. put_prev_set_next_task() then hands the stale server to whatever the
> restarted pick takes.
> 
> Since b3a2dfa8b42e ("sched/fair: Add newidle balance to pick_task_fair()"),
> fair_server_pick_task() returns RETRY_TASK when the newidle balance released
> the rq lock and a higher class task was enqueued meanwhile.
> 
> That task, an RT task for example, then carries the fair server in
> p->dl_server until it is next put. The RV deadline monitors see the fair
> server switch in with it, and core scheduling, if enabled meanwhile, treats
> the task as deadline priority.
> 
> Don't record the server when its pick returns RETRY_TASK. The restarted pick
> records whichever server it goes through, if any.
> 
> Verified with a synthetic reproducer.
> 
> Fixes: b3a2dfa8b42e ("sched/fair: Add newidle balance to pick_task_fair()")
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>

Ugh, please ignore this one. Sent out the wrong patch. I'll test Juri's.

Thanks.

-- 
tejun