From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Neeraj Upadhyay <neeraj.upadhyay@amd.com>,
Steven Rostedt <rostedt@goodmis.org>,
Uladzislau Rezki <urezki@gmail.com>, rcu <rcu@vger.kernel.org>,
Zqiang <qiang.zhang1211@gmail.com>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
matz@suse.de, ubizjak@gmail.com
Subject: Re: [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics
Date: Tue, 31 Oct 2023 11:12:01 -0700 [thread overview]
Message-ID: <e4896e0b-eacc-45a2-a7a8-de2280a51ecc@paulmck-laptop> (raw)
In-Reply-To: <20231031152033.GC15024@noisy.programming.kicks-ass.net>
On Tue, Oct 31, 2023 at 04:20:33PM +0100, Peter Zijlstra wrote:
> On Tue, Oct 31, 2023 at 07:24:13AM -0700, Paul E. McKenney wrote:
>
> > So, at least until GCC catches up to clang's code generation, I take it
> > that you don't want WRITE_ONCE() for that ->nvcsw increment. Thoughts on
> > ->on_rq?
>
> I've not done the patch yet, but I suspect those would be fine, those
> are straight up stores, hard to get wrong (famous last words).
Assuming that the reads are already either marked with READ_ONCE() or
are under appropriate locks, my immediate thought would be something
like the all-too-lightly tested patch shown below.
The ASSERT_EXCLUSIVE_WRITER() causes KCSAN to complain if there is a
concurrent store of any kind to the location.
Of course, please feel free to ignore. Thoughts?
Thanx, Paul
------------------------------------------------------------------------
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 81885748871d..aeace19ad7f5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2124,12 +2124,14 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
enqueue_task(rq, p, flags);
- p->on_rq = TASK_ON_RQ_QUEUED;
+ WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
+ ASSERT_EXCLUSIVE_WRITER(p->on_rq);
}
void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
- p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;
+ WRITE_ONCE(p->on_rq, (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING);
+ ASSERT_EXCLUSIVE_WRITER(p->on_rq);
dequeue_task(rq, p, flags);
}
next prev parent reply other threads:[~2023-10-31 18:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20231027144050.110601-1-frederic@kernel.org>
[not found] ` <20231027144050.110601-3-frederic@kernel.org>
2023-10-27 19:20 ` [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics Peter Zijlstra
2023-10-27 21:23 ` Paul E. McKenney
2023-10-27 22:46 ` Peter Zijlstra
2023-10-27 23:41 ` Paul E. McKenney
2023-10-30 8:21 ` Peter Zijlstra
2023-10-30 20:11 ` Paul E. McKenney
2023-10-31 9:52 ` Peter Zijlstra
2023-10-31 14:16 ` Michael Matz
2023-10-31 14:43 ` Paul E. McKenney
2023-10-31 15:16 ` Peter Zijlstra
2023-10-31 15:55 ` Michael Matz
2023-10-31 16:23 ` Peter Zijlstra
2023-10-31 16:49 ` Michael Matz
2023-10-31 17:10 ` Paul E. McKenney
2023-10-31 14:24 ` Paul E. McKenney
2023-10-31 15:20 ` Peter Zijlstra
2023-10-31 18:12 ` Paul E. McKenney [this message]
2023-10-27 19:23 ` [PATCH 0/4] rcu: Fix PF_IDLE related issues v3 Peter Zijlstra
2023-10-24 21:46 [PATCH 0/4] rcu: Fix PF_IDLE related issues v2 Frederic Weisbecker
2023-10-24 21:46 ` [PATCH 2/4] rcu/tasks: Handle new PF_IDLE semantics Frederic Weisbecker
2023-10-25 8:40 ` Peter Zijlstra
2023-10-25 10:31 ` Frederic Weisbecker
2023-10-26 12:15 ` Z qiang
2023-10-26 14:34 ` Frederic Weisbecker
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