Linux-rt-users archive on lore.kernel.org
 help / color / Atom feed
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
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

  reply index

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

Reply instructions:

You may reply publically 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=20191009072745.GI19588@localhost.localdomain \
    --to=juri.lelli@redhat.com \
    --cc=bigeasy@linutronix.de \
    --cc=bristot@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=swood@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=williams@redhat.com \
    /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

Linux-rt-users archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rt-users/0 linux-rt-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rt-users linux-rt-users/ https://lore.kernel.org/linux-rt-users \
		linux-rt-users@vger.kernel.org
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rt-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git