linux-kernel - Re: [RFC] should VM_BUG_ON(cond) really evaluate cond

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Message-ID: <CA+55aFy9oJSK99K=brRzSfSnLocO=PuS7yuKkAcw3t5hATJrfw@mail.gmail.com>
Date:	Thu, 27 Oct 2011 18:34:48 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] should VM_BUG_ON(cond) really evaluate cond

On Thu, Oct 27, 2011 at 6:25 PM, Andi Kleen <andi@...stfloor.org> wrote:
>
> Seems reasonable too. In fact we usually should have memory barriers
> for this anyways which obsolete the volatile.

No we shouldn't. Memory barriers are insanely expensive, and pointless
for atomics - that aren't ordered anyway.

You may mean compiler barriers.

That said, removing the volatile entirely might be a good idea, and
never mind any barriers at all. The ordering for atomics really isn't
well enough specified that we should care. So I wouldn't object to a
patch that just removes the volatile entirely, but it would have to be
accompanied with quite a bit of testing, in case some odd case ends up
depending on it. But nothing *should* be looping on those things
anyway.

                       Linus
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