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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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