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From: Peter Zijlstra <peterz@infradead.org>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	"Paul E. McKenney" <paulmck@linux.ibm.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v2] sched: Use READ_ONCE()/WRITE_ONCE() in move_queued_task()/task_rq_lock()
Date: Fri, 1 Feb 2019 09:26:48 +0100	[thread overview]
Message-ID: <20190201082647.GA31498@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190121155240.27173-1-andrea.parri@amarulasolutions.com>

On Mon, Jan 21, 2019 at 04:52:40PM +0100, Andrea Parri wrote:
> move_queued_task() synchronizes with task_rq_lock() as follows:
> 
> 	move_queued_task()		task_rq_lock()
> 
> 	[S] ->on_rq = MIGRATING		[L] rq = task_rq()
> 	WMB (__set_task_cpu())		ACQUIRE (rq->lock);
> 	[S] ->cpu = new_cpu		[L] ->on_rq
> 
> where "[L] rq = task_rq()" is ordered before "ACQUIRE (rq->lock)" by an
> address dependency and, in turn, "ACQUIRE (rq->lock)" is ordered before
> "[L] ->on_rq" by the ACQUIRE itself.
> 
> Use READ_ONCE() to load ->cpu in task_rq() (c.f., task_cpu()) to honor
> this address dependency.  Also, mark the accesses to ->cpu and ->on_rq
> with READ_ONCE()/WRITE_ONCE() to comply with the LKMM.
> 
> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>

Thanks!

  parent reply	other threads:[~2019-02-01  8:27 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-21 15:52 [PATCH v2] sched: Use READ_ONCE()/WRITE_ONCE() in move_queued_task()/task_rq_lock() Andrea Parri
2019-01-31 18:25 ` Andrea Parri
2019-02-01  8:26 ` Peter Zijlstra [this message]
2019-02-04  9:02 ` [tip:sched/core] sched/core: " tip-bot for Andrea Parri

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