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sched_ext: Fix the running task keeping its protection into bypass

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Protection ends when the scheduler enters bypass, so that bypass scheduling
can cut every task's slice. scx_bypass() clears it for the queued tasks by
cycling them, and strips the running task's in the same walk over
rq->scx.runnable_list. The running task is never on that list.
set_next_task_scx() takes it off and put_prev_task_scx() puts it back, so
the strip never runs. A protected running task then keeps its slice into
bypass, where the tick's attempts to cut it are refused.

Strip the running task's protection outside the walk.

Fixes: 9cfc6ab34a ("sched_ext: Add SCX_TASK_PROTECTED")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-10-16 19:37:16 -10:00
parent 43e1ef14a4
commit 30fb2b1e4d
1 changed files with 10 additions and 7 deletions
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17
kernel/sched/ext/ext.c
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@ -6318,6 +6318,16 @@ void scx_bypass(struct scx_sched *sch, bool bypass)
continue;
}
/*
* Bypass trumps protection. Cycling the queued tasks below
* clears theirs. The current task isn't on the runnable list,
* so strip its protection here.
*/
p = rq->curr;
if (bypass && p->sched_class == &ext_sched_class &&
scx_is_descendant(scx_task_sched(p), sch))
scx_task_slice_ended(rq, p);
/*
* The use of list_for_each_entry_safe_reverse() is required
* because each task is going to be removed from and added back
@ -6330,13 +6340,6 @@ void scx_bypass(struct scx_sched *sch, bool bypass)
if (!scx_is_descendant(scx_task_sched(p), sch))
continue;
/*
* Bypass trumps protection. Cycling clears for queued
* tasks but current task needs explicit stripping.
*/
if (bypass && task_current(rq, p))
scx_task_slice_ended(rq, p);
/* cycling deq/enq is enough, see the function comment */
scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
/* nothing */ ;