linux-kernel - Re: [PATCH 3/3] kref: Remove the memory barriers

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Message-ID: <1323767540.9082.4.camel@twins>
Date:	Tue, 13 Dec 2011 10:12:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Greg KH <greg@...ah.com>, Ming Lei <tom.leiming@...il.com>,
	gregkh@...e.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, ostrikov@...dia.com,
	adobriyan@...il.com, eric.dumazet@...il.com, mingo@...e.hu
Subject: Re: [PATCH 3/3] kref: Remove the memory barriers

On Mon, 2011-12-12 at 23:56 +0100, Oliver Neukum wrote:
> I guess I worried not about the increment, but the decrement.
> Which makes me wonder what happens if you don't intend
> to get the kref again, but need to make sure it is usually freed,
> like:
> 
> CPU A                                                           CPU B
> 
> kref_get(p)
> start_io(p)
>                                                                         [interrupt from IO]
>                                                                         kref_put(p)

I would expect that if something was needed here, the io stack would
provide the barriers since the io completion will probably want to
change state set by the start_io thing.

Anyway, I would put this squarely outside the responsibility of kref.
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