Messages in this thread | | | Date | Mon, 30 Jan 2023 14:43:01 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] sched: pick_next_rt_entity(): checked list_entry |
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* Pietro Borrello <borrello@diag.uniroma1.it> wrote:
> Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()") > removed any path which could make pick_next_rt_entity() return NULL. > However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of > pick_next_rt_entity()) still checks the error condition, which can > never happen, since list_entry() never returns NULL. Return > list_first_entry_or_null(queue, ...) to allow BUG to check the only > possible error condition here: the queue being empty which should > never happen. > > Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()") > Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it> > --- > kernel/sched/rt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index ed2a47e4ddae..6088d5d83b75 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1777,7 +1777,7 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq) > BUG_ON(idx >= MAX_RT_PRIO); > > queue = array->queue + idx; > - next = list_entry(queue->next, struct sched_rt_entity, run_list); > + next = list_first_entry_or_null(queue, struct sched_rt_entity, run_list); > > return next;
I'd much rather have something like this:
SCHED_WARN_ON(list_empty(next));
So the debug check is part of CONFIG_SCHED_DEBUG=y, and not if it's turned off. Also, this makes sure we don't crash (BUG_ON()) on the error condition, in the hope of getting debug info out of the system.
Thanks,
Ingo
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