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A retained proxy donor keeps both the donor and mutex owner queued. The check therefore misses a constrained FAIR donor and may stop the tick while its runtime still needs to be enforced. Check the selected donor instead and remove the nr_running restriction. The donor being a queued FAIR task is sufficient to require bandwidth accounting regardless of other runnable tasks. Fixes: af0c8b2bf67b ("sched: Split scheduler and execution contexts") Reported-by: Sashiko Link: https://lore.kernel.org/r/20260713164807.E5ED21F00A3A@smtp.kernel.org Acked-by: John Stultz Signed-off-by: Andrea Righi --- kernel/sched/core.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a0e813abddc28..074dc14c22d5d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1409,11 +1409,8 @@ static void nohz_csd_func(void *info) #endif /* CONFIG_NO_HZ_COMMON */ #ifdef CONFIG_NO_HZ_FULL -static inline bool __need_bw_check(struct rq *rq, struct task_struct *p) +static inline bool __need_bw_check(struct task_struct *p) { - if (rq->nr_running != 1) - return false; - if (p->sched_class != &fair_sched_class) return false; @@ -1462,14 +1459,17 @@ bool sched_can_stop_tick(struct rq *rq) return false; /* - * If there is one task and it has CFS runtime bandwidth constraints - * and it's on the cpu now we don't want to stop the tick. + * If the selected scheduling context has CFS runtime bandwidth + * constraints, don't stop the tick. With proxy execution, rq->donor is + * the selected scheduling context while rq->curr is the task physically + * executing on its behalf. + * * This check prevents clearing the bit if a newly enqueued task here is - * dequeued by migrating while the constrained task continues to run. + * dequeued by migrating while the constrained donor continues to run. * E.g. going from 2->1 without going through pick_next_task(). */ - if (__need_bw_check(rq, rq->curr)) { - if (cfs_task_bw_constrained(rq->curr)) + if (__need_bw_check(rq->donor)) { + if (cfs_task_bw_constrained(rq->donor)) return false; } -- 2.55.0