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When switching from a non-EXT task, such as idle, to an EXT task with a finite slice, sched_update_tick_dependency() checks the outgoing task and can allow the tick to remain stopped. The incoming task can then fail to receive the ticks needed to expire its slice. A finite slice is sufficient by itself to require the tick, so set TICK_DEP_BIT_SCHED directly when transitioning to a finite slice. Keep using sched_update_tick_dependency() when transitioning to an infinite slice so that the scheduler evaluates all runqueue requirements before clearing the dependency. Fixes: 22a920209ab6 ("sched_ext: Implement tickless support") Signed-off-by: Andrea Righi --- kernel/sched/ext/ext.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index e75e2fd5ab7e3..dc20a8eed8f6c 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -2982,12 +2982,20 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) */ if ((p->scx.slice == SCX_SLICE_INF) != (bool)(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) { - if (p->scx.slice == SCX_SLICE_INF) + if (p->scx.slice == SCX_SLICE_INF) { rq->scx.flags |= SCX_RQ_CAN_STOP_TICK; - else + sched_update_tick_dependency(rq); + } else { rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK; - sched_update_tick_dependency(rq); + /* + * The rq still references the outgoing scheduling context. + * A finite slice is sufficient by itself to require the tick. + */ + if (tick_nohz_full_cpu(cpu_of(rq))) + tick_nohz_dep_set_cpu(cpu_of(rq), + TICK_DEP_BIT_SCHED); + } /* * For now, let's refresh the load_avgs just when transitioning -- 2.55.0