linux-kernel - Re: [PATCH] make atomic_t volatile on all architectures

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Message-ID: <alpine.LFD.0.999.0708121107490.30176@woody.linux-foundation.org>
Date:	Sun, 12 Aug 2007 11:11:25 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Segher Boessenkool <segher@...nel.crashing.org>
cc:	schwidefsky@...ibm.com, wjiang@...ilience.com,
	wensong@...ux-vs.org, heiko.carstens@...ibm.com,
	linux-kernel@...r.kernel.org, ak@...e.de, cfriesen@...tel.com,
	netdev@...r.kernel.org, horms@...ge.net.au,
	akpm@...ux-foundation.org, Chuck Ebbert <cebbert@...hat.com>,
	davem@...emloft.net, zlynx@....org, Chris Snook <csnook@...hat.com>
Subject: Re: [PATCH] make atomic_t volatile on all architectures

On Sun, 12 Aug 2007, Segher Boessenkool wrote:
> 
> Yeah.  Compiler errors are more annoying though I dare say ;-)

Actually, compile-time errors are fine, and easy to work around. *Much* 
more annoying is when gcc actively generates subtly bad code. We've had 
use-after-free issues due to incorrect gcc liveness calculations etc, and 
inline asm has beeen one of the more common causes - exactly because the 
kernel is one of the few users (along with glibc) that uses it at all.

Now *those* are hard to find - the code works most of the time, but the 
compiler has inserted a really subtle race condition into the code 
(deallocated a local stack entry before last use). We had that with our 
semaphore code at some point.

		Linus
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