On Wed, May 18, 2016 at 04:12:15PM +0100, David Howells wrote:
> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
> index be0a05913b91..1cbddef2b3f3 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -81,7 +81,7 @@ static inline void
> __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
> new.tickets.tail = old.tickets.tail;
>
> /* try to clear slowpath flag when there are no contenders */
> - cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
> + try_cmpxchg_acquire(&lock->head_tail, old.head_tail,
> new.head_tail);
> }
> }
>
> @@ -107,7 +107,7 @@ static __always_inline void
> arch_spin_lock(arch_spinlock_t *lock)
> {
> register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
>
> - inc = xadd(&lock->tickets, inc);
> + inc = xadd_acquire(&lock->tickets, inc);
> if (likely(inc.head == inc.tail))
> goto out;
>
> @@ -128,19 +128,21 @@ out:
> barrier(); /* make sure nothing creeps before the lock is taken */
> }
>
> -static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
> +static __always_inline bool arch_spin_trylock(arch_spinlock_t *lock)
> {
> arch_spinlock_t old, new;
>
> old.tickets = READ_ONCE(lock->tickets);
> if (!__tickets_equal(old.tickets.head, old.tickets.tail))
> - return 0;
> + return false;
>
> new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
> new.head_tail &= ~TICKET_SLOWPATH_FLAG;
>
> - /* cmpxchg is a full barrier, so nothing can move before it */
> - return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) ==
> old.head_tail;
> + /* Insert an acquire barrier with the cmpxchg so that nothing
> + * can move before it.
> + */
> + return try_cmpxchg_acquire(&lock->head_tail, old.head_tail,
> new.head_tail);
> }
>
> static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
> @@ -151,14 +153,14 @@ static __always_inline void
> arch_spin_unlock(arch_spinlock_t *lock)
>
> BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
>
> - head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
> + head = xadd_release(&lock->tickets.head, TICKET_LOCK_INC);
>
> if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
> head &= ~TICKET_SLOWPATH_FLAG;
> __ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
> }
> } else
> - __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
> + add_release(&lock->tickets.head, TICKET_LOCK_INC,
> UNLOCK_LOCK_PREFIX);
> }
>
> static inline int arch_spin_is_locked(arch_spinlock_t *lock)
>
This is all very dead code, I should do a patch removing it.
