On 01/15, Christian Borntraeger wrote:

Am 15.01.2015 um 20:38 schrieb Oleg Nesterov:

quoted

On 01/15, Christian Borntraeger wrote:

quoted

--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h

@@ -186,7 +186,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 	__ticket_t head = ACCESS_ONCE(lock->tickets.head);

 	for (;;) {
-		struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+		struct __raw_tickets tmp = READ_ONCE(lock->tickets);

Agreed, but what about another ACCESS_ONCE() above?

Oleg.

tickets.head is a scalar type, so ACCESS_ONCE does work fine with gcc 4.6/4.7.
My goal was to convert all accesses on non-scalar types

I understand, but READ_ONCE(lock->tickets.head) looks better anyway and
arch_spin_lock() already use READ_ONCE() for this.

So why we should keep the last ACCESS_ONCE() in spinlock.h ? Just to make
another cosmetic cleanup which touches the same function later?

Oleg.