linux-kernel - Re: [PATCH] ipc/msg: Implement lockless pipelined wakeups

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Message-ID: <5638C099.3040706@linutronix.de>
Date:	Tue, 3 Nov 2015 15:11:37 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Davidlohr Bueso <dave@...olabs.net>,
	George Spelvin <linux@...izon.com>
Cc:	tglx@...utronix.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, manfred@...orfullife.com,
	peterz@...radead.org
Subject: Re: [PATCH] ipc/msg: Implement lockless pipelined wakeups

On 10/31/2015 07:54 PM, Davidlohr Bueso wrote:
>> However, a wake_q keeps a reference to a task, so exiting is
>> not a danger.  As long as wake_q_add precedes setting r_msg,
>> all is well.
> 
> Yes, and this confirms that we still rely on the implicit barrier
> from the cmpxchg as tglx mentioned. As such, we also need to keep
> the pairing when reading 'r_msg' in do_msgrcv(), instead of dropping
> the comments.

Okay, I took the memory-barrier comment from your mqueue patch and
adjusted.

> 
> Thanks,
> Davidlohr

Sebastian
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