arm/spinlock: Replace ACCESS_ONCE with READ_ONCE

borntraeger · borntraeger · commit 488beef1440e · 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/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
@@ -120,12 +120,12 @@ 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)
 {
-	struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);
+	struct __raw_tickets tickets = READ_ONCE(lock->tickets);
 	return (tickets.next - tickets.owner) > 1;
 }
 #define arch_spin_is_contended	arch_spin_is_contended

Original file line number	Diff line number	Diff line change
`@@ -120,12 +120,12 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock)`
`120`	`120`
`121`	`121`	`static inline int arch_spin_is_locked(arch_spinlock_t *lock)`
`122`	`122`	`{`
`123`		`- return !arch_spin_value_unlocked(ACCESS_ONCE(*lock));`
	`123`	`+ return !arch_spin_value_unlocked(READ_ONCE(*lock));`
`124`	`124`	`}`
`125`	`125`
`126`	`126`	`static inline int arch_spin_is_contended(arch_spinlock_t *lock)`
`127`	`127`	`{`
`128`		`- struct __raw_tickets tickets = ACCESS_ONCE(lock->tickets);`
	`128`	`+ struct __raw_tickets tickets = READ_ONCE(lock->tickets);`
`129`	`129`	`return (tickets.next - tickets.owner) > 1;`
`130`	`130`	`}`
`131`	`131`	`#define arch_spin_is_contended arch_spin_is_contended`