linux-kernel - Re: [PATCH 0/5] x86-32: improve atomic64

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Date:	Sun, 28 Feb 2010 23:35:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Luca Barbieri <luca@...a-barbieri.com>,
	Paul Mackerras <paulus@...ba.org>
CC:	Ingo Molnar <mingo@...e.hu>, a.p.zijlstra@...llo.nl,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] x86-32: improve atomic64_t functions (v2)

On 02/26/2010 03:23 AM, Luca Barbieri wrote:
> Sent patches, both to conditionally perform the test and implement the
> functions for x86 and x86-64.

Yes, and with the test turned on, the kernel crashes immediately on boot
on x86-64.

Some minor investigation reveals the following:

lib/atomic64.c has the wrong return value for atomic64_add_unless().
With "wrong" I mean it is the opposite sense compared to
atomic_add_unless(), not just on x86 but on all architectures.

Accordingly, I have to conclude that lib/atomic64.c is buggy, and that
since your test matches that bug, I will have to conclude that your
x86-32 implementation is also buggy.  Thus, please send patches to fix
your test and your 32-bit implementations (and preferrably
lib/atomic64.c too, but I can do that just fine.)

Cc: Paul Mackerras who did the generic atomic64_t implementation for
verification that this is indeed a bug.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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