[ 039/102] ARM: 7720/1: ARM v6/v7 cmpxchg64 shouldnt clear upper 32 bits of the old/new value

From: Greg Kroah-Hartman
Date: Fri May 17 2013 - 18:18:50 EST

3.9-stable review patch. If anyone has any objections, please let me know.


From: Jaccon Bastiaansen <jaccon.bastiaansen@xxxxxxxxx>

commit 6eabb3301b1facee669d9938f7c5a0295c21d71d upstream.

The implementation of cmpxchg64() for the ARM v6 and v7 architecture
casts parameter 2 and 3 (the old and new 64bit values) to an unsigned
long before calling the atomic_cmpxchg64() function. This clears
the top 32 bits of the old and new values, resulting in the wrong
values being compare-exchanged. Luckily, this only appears to be used
for 64-bit sched_clock, which we don't (yet) have on ARM.

This bug was introduced by commit 3e0f5a15f500 ("ARM: 7404/1: cmpxchg64:
use atomic64 and local64 routines for cmpxchg64").

Acked-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Jaccon Bastiaansen <jaccon.bastiaansen@xxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/arm/include/asm/cmpxchg.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/arch/arm/include/asm/cmpxchg.h
+++ b/arch/arm/include/asm/cmpxchg.h
@@ -233,15 +233,15 @@ static inline unsigned long __cmpxchg_lo
((__typeof__(*(ptr)))atomic64_cmpxchg(container_of((ptr), \
atomic64_t, \
counter), \
- (unsigned long)(o), \
- (unsigned long)(n)))
+ (unsigned long long)(o), \
+ (unsigned long long)(n)))

#define cmpxchg64_local(ptr, o, n) \
((__typeof__(*(ptr)))local64_cmpxchg(container_of((ptr), \
local64_t, \
a), \
- (unsigned long)(o), \
- (unsigned long)(n)))
+ (unsigned long long)(o), \
+ (unsigned long long)(n)))

#endif /* __LINUX_ARM_ARCH__ >= 6 */

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