From: Juri Lelli <juri.lelli@redhat.com>
To: Scott Wood <swood@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Clark Williams <williams@redhat.com>,
linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Subject: Re: [PATCH RT 5/8] sched/deadline: Reclaim cpuset bandwidth in .migrate_task_rq()
Date: Wed, 9 Oct 2019 09:27:45 +0200 [thread overview]
Message-ID: <20191009072745.GI19588@localhost.localdomain> (raw)
In-Reply-To: <a1098e5f95a1ab202fdf79a73aedfeeb8e02dd47.camel@redhat.com>
On 09/10/19 01:25, Scott Wood wrote:
> On Tue, 2019-10-01 at 10:52 +0200, Juri Lelli wrote:
> > On 30/09/19 11:24, Scott Wood wrote:
> > > On Mon, 2019-09-30 at 09:12 +0200, Juri Lelli wrote:
> >
> > [...]
> >
> > > > Hummm, I was actually more worried about the fact that we call
> > > > free_old_
> > > > cpuset_bw_dl() only if p->state != TASK_WAKING.
> > >
> > > Oh, right. :-P Not sure what I had in mind there; we want to call it
> > > regardless.
> > >
> > > I assume we need rq->lock in free_old_cpuset_bw_dl()? So something like
> >
> > I think we can do with rcu_read_lock_sched() (see dl_task_can_attach()).
>
> RCU will keep dl_bw from being freed under us (we're implicitly in an RCU
> sched read section due to atomic context). It won't stop rq->rd from
> changing, but that could have happened before we took rq->lock. If the cpu
> the task was running on was removed from the cpuset, and that raced with the
> task being moved to a different cpuset, couldn't we end up erroneously
> subtracting from the cpu's new root domain (or failing to subtract at all if
> the old cpu's new cpuset happens to be the task's new cpuset)? I don't see
> anything that forces tasks off of the cpu when a cpu is removed from a
> cpuset (though maybe I'm not looking in the right place), so the race window
> could be quite large. In any case, that's an existing problem that's not
> going to get solved in this patchset.
OK. So, mainline has got cpuset_read_lock() which should be enough to
guard against changes to rd(s).
I agree that rq->lock is needed here.
Thanks,
Juri
next prev parent reply other threads:[~2019-10-09 7:27 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-27 5:56 [RT PATCH 0/8] migrate disable fixes and performance Scott Wood
2019-07-27 5:56 ` [PATCH RT 1/8] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Scott Wood
2019-07-29 13:26 ` Steven Rostedt
2019-07-27 5:56 ` [PATCH RT 2/8] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus_ptr Scott Wood
2019-09-17 14:57 ` Sebastian Andrzej Siewior
2019-09-17 15:23 ` Scott Wood
2019-07-27 5:56 ` [PATCH RT 3/8] sched: Remove dead __migrate_disabled() check Scott Wood
2019-07-27 5:56 ` [PATCH RT 4/8] sched: migrate disable: Protect cpus_ptr with lock Scott Wood
2019-09-26 16:39 ` Sebastian Andrzej Siewior
2019-09-26 16:52 ` Scott Wood
2019-09-27 12:19 ` Sebastian Andrzej Siewior
2019-09-27 20:02 ` Scott Wood
2019-07-27 5:56 ` [PATCH RT 5/8] sched/deadline: Reclaim cpuset bandwidth in .migrate_task_rq() Scott Wood
2019-09-17 15:10 ` Sebastian Andrzej Siewior
2019-09-27 8:11 ` Juri Lelli
2019-09-27 16:40 ` Scott Wood
2019-09-30 7:12 ` Juri Lelli
2019-09-30 16:24 ` Scott Wood
2019-10-01 8:52 ` Juri Lelli
2019-10-09 6:25 ` Scott Wood
2019-10-09 7:27 ` Juri Lelli [this message]
2019-10-09 19:12 ` Scott Wood
2019-10-10 8:18 ` Juri Lelli
2019-07-27 5:56 ` [PATCH RT 6/8] sched: migrate_enable: Set state to TASK_RUNNING Scott Wood
2019-09-17 15:31 ` Sebastian Andrzej Siewior
2019-09-17 17:54 ` Scott Wood
2019-07-27 5:56 ` [PATCH RT 7/8] sched: migrate_enable: Use select_fallback_rq() Scott Wood
2019-09-17 16:00 ` Sebastian Andrzej Siewior
2019-09-24 18:05 ` Scott Wood
2019-07-27 5:56 ` [PATCH RT 8/8] sched: Lazy migrate_disable processing Scott Wood
2019-09-17 16:50 ` Sebastian Andrzej Siewior
2019-09-17 17:06 ` Scott Wood
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