From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Valentin Schneider <valentin.schneider@arm.com>,
linux-kernel@vger.kernel.org
Cc: John Keeping <john@metanate.com>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [PATCH] sched/rt: Plug rt_mutex_setprio() vs push_rt_task() race
Date: Mon, 24 Jan 2022 10:37:43 +0100 [thread overview]
Message-ID: <aa5bf2d0-bef7-485a-9a51-0da7df67d8c5@arm.com> (raw)
In-Reply-To: <20220120194037.650433-1-valentin.schneider@arm.com>
On 20/01/2022 20:40, Valentin Schneider wrote:
[...]
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 7b4f4fbbb404..48fc8c04b038 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2026,6 +2026,16 @@ static int push_rt_task(struct rq *rq, bool pull)
> return 0;
>
> retry:
> + /*
> + * It's possible that the next_task slipped in of
> + * higher priority than current. If that's the case
> + * just reschedule current.
> + */
> + if (unlikely(next_task->prio < rq->curr->prio)) {
> + resched_curr(rq);
> + return 0;
> + }
If we do this before `is_migration_disabled(next_task), shouldn't then
the related condition in push_dl_task() also be moved up?
if (dl_task(rq->curr) &&
dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
rq->curr->nr_cpus_allowed > 1)
To enforce resched_curr(rq) in the `is_migration_disabled(next_task)`
case there as well?
> +
> if (is_migration_disabled(next_task)) {
> struct task_struct *push_task = NULL;
> int cpu;
> @@ -2033,6 +2043,17 @@ static int push_rt_task(struct rq *rq, bool pull)
> if (!pull || rq->push_busy)
> return 0;
>
> + /*
> + * Per the above priority check, curr is at least RT. If it's
> + * of a higher class than RT, invoking find_lowest_rq() on it
> + * doesn't make sense.
> + *
> + * Note that the stoppers are masqueraded as SCHED_FIFO
> + * (cf. sched_set_stop_task()), so we can't rely on rt_task().
> + */
> + if (rq->curr->sched_class != &rt_sched_class)
s/ != / > / ... since the `unlikely(next_task->prio < rq->curr->prio)`
already filters tasks from lower sched classes (CFS)?
> + return 0;
> +
[...]
next prev parent reply other threads:[~2022-01-24 9:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-20 19:40 [PATCH] sched/rt: Plug rt_mutex_setprio() vs push_rt_task() race Valentin Schneider
2022-01-20 19:47 ` Valentin Schneider
2022-01-21 19:47 ` John Keeping
2022-01-24 12:39 ` Valentin Schneider
2022-01-24 9:37 ` Dietmar Eggemann [this message]
2022-01-24 13:29 ` Valentin Schneider
2022-01-24 15:47 ` Dietmar Eggemann
2022-01-24 16:51 ` Valentin Schneider
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