* (the type definitions are in asm/spinlock_types.h)
*/
-#ifdef CONFIG_X86_32
-# define LOCK_PTR_REG "a"
-#else
-# define LOCK_PTR_REG "D"
-#endif
-
-#if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
-/*
- * On PPro SMP, we use a locked operation to unlock
- * (PPro errata 66, 92)
- */
-# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
-#else
-# define UNLOCK_LOCK_PREFIX
-#endif
-
/* How long a lock should spin before we consider blocking */
#define SPIN_THRESHOLD (1 << 15)
extern struct static_key paravirt_ticketlocks_enabled;
static __always_inline bool static_key_false(struct static_key *key);
-#ifdef CONFIG_QUEUED_SPINLOCKS
#include <asm/qspinlock.h>
-#else
-
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-
-static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
-{
- set_bit(0, (volatile unsigned long *)&lock->tickets.head);
-}
-
-#else /* !CONFIG_PARAVIRT_SPINLOCKS */
-static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
- __ticket_t ticket)
-{
-}
-static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
- __ticket_t ticket)
-{
-}
-
-#endif /* CONFIG_PARAVIRT_SPINLOCKS */
-static inline int __tickets_equal(__ticket_t one, __ticket_t two)
-{
- return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
-}
-
-static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
- __ticket_t head)
-{
- if (head & TICKET_SLOWPATH_FLAG) {
- arch_spinlock_t old, new;
-
- old.tickets.head = head;
- new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
- old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
- 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);
- }
-}
-
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
- return __tickets_equal(lock.tickets.head, lock.tickets.tail);
-}
-
-/*
- * Ticket locks are conceptually two parts, one indicating the current head of
- * the queue, and the other indicating the current tail. The lock is acquired
- * by atomically noting the tail and incrementing it by one (thus adding
- * ourself to the queue and noting our position), then waiting until the head
- * becomes equal to the the initial value of the tail.
- *
- * We use an xadd covering *both* parts of the lock, to increment the tail and
- * also load the position of the head, which takes care of memory ordering
- * issues and should be optimal for the uncontended case. Note the tail must be
- * in the high part, because a wide xadd increment of the low part would carry
- * up and contaminate the high part.
- */
-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);
- if (likely(inc.head == inc.tail))
- goto out;
-
- for (;;) {
- unsigned count = SPIN_THRESHOLD;
-
- do {
- inc.head = READ_ONCE(lock->tickets.head);
- if (__tickets_equal(inc.head, inc.tail))
- goto clear_slowpath;
- cpu_relax();
- } while (--count);
- __ticket_lock_spinning(lock, inc.tail);
- }
-clear_slowpath:
- __ticket_check_and_clear_slowpath(lock, inc.head);
-out:
- barrier(); /* make sure nothing creeps before the lock is taken */
-}
-
-static __always_inline int 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;
-
- 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;
-}
-
-static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
- if (TICKET_SLOWPATH_FLAG &&
- static_key_false(¶virt_ticketlocks_enabled)) {
- __ticket_t head;
-
- BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
-
- head = xadd(&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);
-}
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
- struct __raw_tickets tmp = READ_ONCE(lock->tickets);
-
- return !__tickets_equal(tmp.tail, tmp.head);
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
- struct __raw_tickets tmp = READ_ONCE(lock->tickets);
-
- tmp.head &= ~TICKET_SLOWPATH_FLAG;
- return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
-}
-#define arch_spin_is_contended arch_spin_is_contended
-
-static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
- unsigned long flags)
-{
- arch_spin_lock(lock);
-}
-
-static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
-{
- __ticket_t head = READ_ONCE(lock->tickets.head);
-
- for (;;) {
- struct __raw_tickets tmp = READ_ONCE(lock->tickets);
- /*
- * We need to check "unlocked" in a loop, tmp.head == head
- * can be false positive because of overflow.
- */
- if (__tickets_equal(tmp.head, tmp.tail) ||
- !__tickets_equal(tmp.head, head))
- break;
-
- cpu_relax();
- }
-}
-#endif /* CONFIG_QUEUED_SPINLOCKS */
/*
* Read-write spinlocks, allowing multiple readers
projects / cascardo / linux.git / blobdiff