From: trd@45mercystreet.com (Toby Douglass)
To: linux-arm-kernel@lists.infradead.org
Subject: CAS implementation may be broken
Date: Thu, 26 Nov 2009 17:14:19 +0100 [thread overview]
Message-ID: <4B0EA95B.20401@45mercystreet.com> (raw)
In-Reply-To: <20091125012406.GB13142@shareable.org>
Jamie Lokier wrote:
> Toby Douglass wrote:
>> Interestingly, I saw a day or two ago that there is a double-word
>> version of LDREX. The atomic-ptr project, which forms the basis of the
>> GCC garbage collector, relies on this; it does not in fact use LL/SC on
>> ARM, but rather uses double-word CAS using a pointer-counter pair.
> Note that pointer-counter is not really reliable.
[snip case]
> Of course even if the counter wraps, you still have to be 1/2^32
> unlucky to see the same value. But that's enough to make it unreliable.
I concur, but it's not a problem on 64-bit.
next prev parent reply other threads:[~2009-11-26 16:14 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-04 18:09 GCC built-in atomic operations and memory barriers Toby Douglass
2009-11-04 19:05 ` Russell King - ARM Linux
2009-11-04 20:12 ` Toby Douglass
2009-11-04 21:03 ` Russell King - ARM Linux
2009-11-06 19:10 ` Toby Douglass
2009-11-04 22:09 ` Gilles Chanteperdrix
2009-11-06 19:17 ` Toby Douglass
2009-11-21 15:21 ` CAS implementation may be broken Toby Douglass
2009-11-23 15:08 ` Russell King - ARM Linux
2009-11-23 19:10 ` Toby Douglass
2009-11-23 20:06 ` Russell King - ARM Linux
2009-11-23 20:34 ` Toby Douglass
2009-11-23 15:13 ` Catalin Marinas
2009-11-24 15:15 ` Toby Douglass
2009-11-24 15:36 ` Russell King - ARM Linux
2009-11-24 16:20 ` Toby Douglass
2009-11-24 16:27 ` Catalin Marinas
2009-11-24 17:14 ` Toby Douglass
2009-11-25 1:24 ` Jamie Lokier
2009-11-26 16:14 ` Toby Douglass [this message]
2009-11-27 1:37 ` Jamie Lokier
2009-11-24 15:33 ` Toby Douglass
2009-11-23 15:34 ` Catalin Marinas
2009-11-23 16:40 ` Toby Douglass
2009-11-23 22:28 ` Jamie Lokier
2009-11-23 23:13 ` Russell King - ARM Linux
2009-11-24 1:32 ` Jamie Lokier
2009-11-24 11:19 ` Catalin Marinas
2009-11-24 22:24 ` Toby Douglass
2009-11-25 11:11 ` Catalin Marinas
2009-11-25 18:57 ` Toby Douglass
2009-11-24 22:34 ` Toby Douglass
2009-11-24 22:56 ` Russell King - ARM Linux
2009-11-25 0:34 ` Toby Douglass
2009-11-24 9:38 ` Toby Douglass
2009-11-24 15:59 ` Catalin Marinas
2009-11-24 16:34 ` Toby Douglass
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