From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: [RFC] should VM_BUG_ON(cond) really evaluate cond Date: Thu, 27 Oct 2011 18:34:48 -0700 Message-ID: References: <1319764761.23112.14.camel@edumazet-laptop> <20111028012521.GF25795@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Eric Dumazet , linux-kernel , netdev , Andrew Morton To: Andi Kleen Return-path: In-Reply-To: <20111028012521.GF25795@one.firstfloor.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Oct 27, 2011 at 6:25 PM, Andi Kleen 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