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 access the lock with a barrier.
Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
---
arch/arm64/include/asm/spinlock.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/spinlock.h
b/arch/arm64/include/asm/spinlock.h
index c45b7b1..f72dc64 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -99,12 +99,15 @@ 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));
+ arch_spinlock_t lockval = *lock;
+ barrier();
+ return !arch_spin_value_unlocked(lockval);
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
- arch_spinlock_t lockval = ACCESS_ONCE(*lock);
+ arch_spinlock_t lockval = *lock;
+ barrier();
return (lockval.next - lockval.owner) > 1;
}
#define arch_spin_is_contended arch_spin_is_contended
--
1.9.3
--
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