From: Valentin Schneider <valentin.schneider@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>,
John Keeping <john@metanate.com>,
linux-rt-users@vger.kernel.org
Cc: 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>,
linux-kernel@vger.kernel.org
Subject: Re: [RT] BUG in sched/cpupri.c
Date: Tue, 21 Dec 2021 16:11:34 +0000 [thread overview]
Message-ID: <87zgou6iq1.mognet@arm.com> (raw)
In-Reply-To: <71ddbe51-2b7f-2b13-5f22-9013506471dc@arm.com>
On 20/12/21 18:35, Dietmar Eggemann wrote:
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index ef8228d19382..798887f1eeff 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1895,9 +1895,17 @@ static int push_rt_task(struct rq *rq, bool pull)
> struct task_struct *push_task = NULL;
> int cpu;
>
> + if (WARN_ON_ONCE(!rt_task(rq->curr))) {
> + printk("next_task=[%s %d] rq->curr=[%s %d]\n",
> + next_task->comm, next_task->pid, rq->curr->comm, rq->curr->pid);
> + }
> +
> if (!pull || rq->push_busy)
> return 0;
>
> + if (!rt_task(rq->curr))
> + return 0;
> +
If current is a DL/stopper task, why not; if that's CFS (which IIUC is your
case), that's buggered: we shouldn't be trying to pull RT tasks when we
have queued RT tasks and a less-than-RT current, we should be rescheduling
right now.
I'm thinking this can happen via rt_mutex_setprio() when we demote an RT-boosted
CFS task (or straight up sched_setscheduler()):
check_class_changed()->switched_from_rt() doesn't trigger a resched_curr(),
so I suspect we get to the push/pull callback before getting a
resched (I actually don't see where we'd get a resched in that case other
than at the next tick).
IOW, feels like we want the below. Unfortunately I can't reproduce the
issue locally (yet), so that's untested.
---
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fd7c4f972aaf..7d61ceec1a3b 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2467,10 +2467,13 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
* this is the right place to try to pull some other one
* from an overloaded CPU, if any.
*/
- if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
+ if (!task_on_rq_queued(p))
return;
- deadline_queue_pull_task(rq);
+ if (!rq->dl.dl_nr_running)
+ deadline_queue_pull_task(rq);
+ else if (task_current(rq, p) && (p->sched_class < &dl_sched_class))
+ resched_curr(rq);
}
/*
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index ef8228d19382..1ea2567612fb 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2322,10 +2322,13 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p)
* we may need to handle the pulling of RT tasks
* now.
*/
- if (!task_on_rq_queued(p) || rq->rt.rt_nr_running)
+ if (!task_on_rq_queued(p))
return;
- rt_queue_pull_task(rq);
+ if (!rq->rt.rt_nr_running)
+ rt_queue_pull_task(rq);
+ else if (task_current(rq, p) && (p->sched_class < &rt_sched_class))
+ resched_curr(rq);
}
void __init init_sched_rt_class(void)
next prev parent reply other threads:[~2021-12-21 16:11 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-18 14:25 [RT] BUG in sched/cpupri.c John Keeping
2021-12-20 17:35 ` Dietmar Eggemann
2021-12-21 16:11 ` Valentin Schneider [this message]
2021-12-21 16:45 ` John Keeping
2021-12-21 17:22 ` Valentin Schneider
2021-12-21 17:42 ` John Keeping
2021-12-22 17:46 ` Dietmar Eggemann
2021-12-22 18:45 ` John Keeping
2021-12-22 19:48 ` Valentin Schneider
2021-12-23 11:58 ` John Keeping
2021-12-23 14:05 ` Valentin Schneider
2022-01-07 10:46 ` Dietmar Eggemann
2022-01-07 11:49 ` John Keeping
2022-01-07 14:25 ` Dietmar Eggemann
2022-01-07 18:35 ` John Keeping
2022-01-14 18:25 ` Valentin Schneider
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87zgou6iq1.mognet@arm.com \
--to=valentin.schneider@arm.com \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=john@metanate.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).