linux-kernel - [117/205] ARM: 6211/1: atomic ops: fix register constraints for atomic64_add

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Message-Id: <20100730175144.580602183@clark.site>
Date:	Fri, 30 Jul 2010 10:52:14 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Will Deacon <will.deacon@....com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: [117/205] ARM: 6211/1: atomic ops: fix register constraints for atomic64_add_unless

2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Will Deacon <will.deacon@....com>

commit 068de8d1be48a04b92fd97f76bb7e113b7be82a8 upstream.

The atomic64_add_unless function compares an atomic variable with
a given value and, if they are not equal, adds another given value
to the atomic variable. The function returns zero if the addition
did not occur and non-zero otherwise.

On ARM, the return value is initialised to 1 in C code. Inline assembly
code then performs the atomic64_add_unless operation, setting the
return value to 0 iff the addition does not occur. This means that
when the addition *does* occur, the value of ret must be preserved
across the inline assembly and therefore requires a "+r" constraint
rather than the current one of "=&r".

Thanks to Nicolas Pitre for helping to spot this.

Reviewed-by: Nicolas Pitre <nicolas.pitre@...aro.org>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/arm/include/asm/atomic.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/include/asm/atomic.h
+++ b/arch/arm/include/asm/atomic.h
@@ -440,7 +440,7 @@ static inline int atomic64_add_unless(at
 "	teq	%2, #0\n"
 "	bne	1b\n"
 "2:"
-	: "=&r" (val), "=&r" (ret), "=&r" (tmp)
+	: "=&r" (val), "+r" (ret), "=&r" (tmp)
 	: "r" (&v->counter), "r" (u), "r" (a)
 	: "cc");

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