LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Chris Metcalf <cmetcalf@ezchip.com>,
	Christoph Lameter <cl@linux.com>, Kirill Tkhai <tkhai@yandex.ru>,
	Mike Galbraith <efault@gmx.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: Re: [PATCH 2/3] task: RCU protect tasks on the runqueue
Date: Tue, 3 Sep 2019 22:06:03 +0200
Message-ID: <20190903200603.GW2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHk-=wjvyRJEdativFqqGGxzSgWnc-m7b+B04iQBMcZV4uM=hA@mail.gmail.com>

On Tue, Sep 03, 2019 at 12:18:47PM -0700, Linus Torvalds wrote:
> Now, if you can point to some particular field where that ordering
> makes sense for the particular case of "make it active on the
> runqueue" vs "look up the task from the runqueue using RCU", then I do
> think that the whole release->acquire consistency makes sense.
> 
> But it's not clear that such a field exists, particularly when this is
> in no way the *common* way to even get a task pointer, and other paths
> do *not* use the runqueue as the serialization point.

Even if we could find a case (and I'm not seeing one in a hurry), I
would try really hard to avoid adding extra barriers here and instead
make the consumer a little more complicated if at all possible.

The Power folks got rid of a SYNC (yes, more expensive than LWSYNC) from
their __switch_to() implementation and that had a measurable impact.

9145effd626d ("powerpc/64: Drop explicit hwsync in context switch")

  reply index

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30 14:08 [BUG] Use of probe_kernel_address() in task_rcu_dereference() without checking return value Russell King - ARM Linux admin
2019-08-30 15:24 ` Oleg Nesterov
2019-08-30 15:30 ` Linus Torvalds
2019-08-30 15:40   ` Russell King - ARM Linux admin
2019-08-30 15:43     ` Linus Torvalds
2019-08-30 15:41   ` Linus Torvalds
2019-08-30 16:09     ` Oleg Nesterov
2019-08-30 16:21       ` Linus Torvalds
2019-08-30 16:44         ` Oleg Nesterov
2019-08-30 16:58           ` Linus Torvalds
2019-08-30 19:36         ` Eric W. Biederman
2019-09-02 13:40           ` Oleg Nesterov
2019-09-02 13:53             ` Peter Zijlstra
2019-09-02 14:44               ` Oleg Nesterov
2019-09-02 16:20                 ` Peter Zijlstra
2019-09-02 17:04             ` Eric W. Biederman
2019-09-02 17:34               ` Linus Torvalds
2019-09-03  4:50                 ` [PATCH 0/3] task: Making tasks on the runqueue rcu protected Eric W. Biederman
2019-09-03  4:51                   ` [PATCH 1/3] task: Add a count of task rcu users Eric W. Biederman
2019-09-04 14:36                     ` Oleg Nesterov
2019-09-04 14:44                     ` Frederic Weisbecker
2019-09-04 15:32                       ` Oleg Nesterov
2019-09-04 16:33                         ` Frederic Weisbecker
2019-09-04 18:20                           ` Linus Torvalds
2019-09-05 14:59                             ` Frederic Weisbecker
2019-09-03  4:52                   ` [PATCH 2/3] task: RCU protect tasks on the runqueue Eric W. Biederman
2019-09-03  7:41                     ` Peter Zijlstra
2019-09-03  7:47                       ` Peter Zijlstra
2019-09-03 16:44                         ` Eric W. Biederman
2019-09-03 17:08                           ` Linus Torvalds
2019-09-03 18:13                             ` Eric W. Biederman
2019-09-03 19:18                               ` Linus Torvalds
2019-09-03 20:06                                 ` Peter Zijlstra [this message]
2019-09-03 21:32                                   ` Paul E. McKenney
2019-09-05 20:02                                     ` Eric W. Biederman
2019-09-05 20:55                                       ` Paul E. McKenney
2019-09-06  7:07                                       ` Peter Zijlstra
2019-09-09 12:22                                         ` Eric W. Biederman
2019-09-25  7:36                                           ` Peter Zijlstra
2019-09-27  8:10                                   ` [tip: sched/urgent] tasks, sched/core: RCUify the assignment of rq->curr tip-bot2 for Eric W. Biederman
2019-09-03 19:42                               ` [PATCH 2/3] task: RCU protect tasks on the runqueue Peter Zijlstra
2019-09-14 12:31                           ` [PATCH v2 1/4] task: Add a count of task rcu users Eric W. Biederman
2019-09-14 12:31                           ` [PATCH v2 2/4] task: Ensure tasks are available for a grace period after leaving the runqueue Eric W. Biederman
2019-09-14 12:32                           ` [PATCH v2 3/4] task: With a grace period after finish_task_switch, remove unnecessary code Eric W. Biederman
2019-09-04 14:22                     ` [PATCH 2/3] task: RCU protect tasks on the runqueue Frederic Weisbecker
2019-09-03  4:52                   ` [PATCH 3/3] task: Clean house now that tasks on the runqueue are rcu protected Eric W. Biederman
2019-09-03  9:45                     ` kbuild test robot
2019-09-03 13:06                     ` Oleg Nesterov
2019-09-03 13:58                   ` [PATCH 0/3] task: Making tasks on the runqueue " Oleg Nesterov
2019-09-03 15:44                   ` Linus Torvalds
2019-09-03 19:46                     ` Peter Zijlstra
     [not found]                   ` <87muf7f4bf.fsf_-_@x220.int.ebiederm.org>
2019-09-14 12:33                     ` [PATCH v2 1/4] task: Add a count of task rcu users Eric W. Biederman
2019-09-15 13:54                       ` Paul E. McKenney
2019-09-27  8:10                       ` [tip: sched/urgent] tasks: Add a count of task RCU users tip-bot2 for Eric W. Biederman
2019-09-14 12:33                     ` [PATCH v2 2/4] task: Ensure tasks are available for a grace period after leaving the runqueue Eric W. Biederman
2019-09-15 14:07                       ` Paul E. McKenney
2019-09-15 14:09                         ` Paul E. McKenney
2019-09-27  8:10                       ` [tip: sched/urgent] tasks, sched/core: " tip-bot2 for Eric W. Biederman
2019-09-14 12:34                     ` [PATCH v2 3/4] task: With a grace period after finish_task_switch, remove unnecessary code Eric W. Biederman
2019-09-15 14:32                       ` Paul E. McKenney
2019-09-15 17:07                         ` Linus Torvalds
2019-09-15 18:47                           ` Paul E. McKenney
2019-09-27  8:10                       ` [tip: sched/urgent] tasks, sched/core: With a grace period after finish_task_switch(), " tip-bot2 for Eric W. Biederman
2019-09-14 12:35                     ` [PATCH v2 4/4] task: RCUify the assignment of rq->curr Eric W. Biederman
2019-09-15 14:41                       ` Paul E. McKenney
2019-09-15 17:59                         ` Eric W. Biederman
2019-09-15 18:25                           ` Eric W. Biederman
2019-09-15 18:48                             ` Paul E. McKenney
2019-09-20 23:02                       ` Frederic Weisbecker
2019-09-26  1:49                         ` Eric W. Biederman
2019-09-26 12:42                           ` Frederic Weisbecker
2019-09-14 17:43                     ` [PATCH v2 0/4] task: Making tasks on the runqueue rcu protected Linus Torvalds
2019-09-17 17:38                       ` Eric W. Biederman
2019-09-25  7:51                         ` Peter Zijlstra
2019-09-26  1:11                           ` Eric W. Biederman

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=20190903200603.GW2349@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=cl@linux.com \
    --cc=cmetcalf@ezchip.com \
    --cc=dave@stgolabs.net \
    --cc=ebiederm@xmission.com \
    --cc=efault@gmx.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=paulmck@linux.ibm.com \
    --cc=tglx@linutronix.de \
    --cc=tkhai@yandex.ru \
    --cc=torvalds@linux-foundation.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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

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

Example config snippet for mirrors

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


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