arm64/spinlock: Replace ACCESS_ONCE READ_ONCE

borntraeger · borntraeger · commit af2e7aaed1cc · 2014-12-18T09:54:40.000+01:00
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@de.ibm.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git 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

Original file line number	Diff line number	Diff line change
`@@ -99,12 +99,12 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock)`
`99`	`99`
`100`	`100`	`static inline int arch_spin_is_locked(arch_spinlock_t *lock)`
`101`	`101`	`{`
`102`		`- return !arch_spin_value_unlocked(ACCESS_ONCE(*lock));`
	`102`	`+ return !arch_spin_value_unlocked(READ_ONCE(*lock));`
`103`	`103`	`}`
`104`	`104`
`105`	`105`	`static inline int arch_spin_is_contended(arch_spinlock_t *lock)`
`106`	`106`	`{`
`107`		`- arch_spinlock_t lockval = ACCESS_ONCE(*lock);`
	`107`	`+ arch_spinlock_t lockval = READ_ONCE(*lock);`
`108`	`108`	`return (lockval.next - lockval.owner) > 1;`
`109`	`109`	`}`
`110`	`110`	`#define arch_spin_is_contended arch_spin_is_contended`