From: Peter Zijlstra <peterz@infradead.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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 21:42:18 +0200 [thread overview]
Message-ID: <20190903194218.GU2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <874l1tp7st.fsf@x220.int.ebiederm.org>
On Tue, Sep 03, 2019 at 01:13:22PM -0500, Eric W. Biederman wrote:
> I think this is where I am looking a things differently than you and
> Peter. Why does it have to be ___schedule() that changes the value
> in the task_struct? Why can't it be something else that changes the
> value and then proceeds to call schedule()?
If you call schedule() you will pass through plenty that already implies
smp_mb() before writing the ->curr pointer. If you care about that case,
adding RELEASE semantics to that store gains you absolutely nothing
except a marginally slower kernel.
> If we use RCU_INIT_POINTER if there was something that changed
> task_struct and then called schedule() what ensures that a remote cpu
> that has a stale copy of task_struct cached will update it's cache
> after following the new value rq->curr? Don't we need
> rcu_assign_pointer to get that guarantee?
That whole construct doesn't really make sense: one it is very rare to
change task_struct content for !current tasks (and if we do, it must be
with atomic ops, because then there can be concurrency), secondly when
calling schedule() there is no guarantee on what @next will be.
next prev parent reply other threads:[~2019-09-03 19:42 UTC|newest]
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
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 ` Peter Zijlstra [this message]
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
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