[PATCH 6/8] arm64/spinlock: Replace ACCESS_ONCE READ_ONCE

From: Christian Borntraeger
Date: Thu Dec 11 2014 - 09:06:45 EST


ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)

Change the spinlock code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/spinlock.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index c45b7b1..cee1287 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -99,12 +99,12 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock)

static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- return !arch_spin_value_unlocked(ACCESS_ONCE(*lock));
+ return !arch_spin_value_unlocked(READ_ONCE(*lock));
}

static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
- arch_spinlock_t lockval = ACCESS_ONCE(*lock);
+ arch_spinlock_t lockval = READ_ONCE(*lock);
return (lockval.next - lockval.owner) > 1;
}
#define arch_spin_is_contended arch_spin_is_contended
--
1.9.3

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