#ifndef _ASM_X86_SPINLOCK_H
#define _ASM_X86_SPINLOCK_H
#include <linux/atomic.h>
#include <asm/page.h>
#include <asm/processor.h>
#include <linux/compiler.h>
#include <asm/paravirt.h>
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
*
* Simple spin lock operations. There are two variants, one clears IRQ's
* on the local processor, one does not.
*
* These are fair FIFO ticket locks, which are currently limited to 256
* CPUs.
*
* (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_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE))
/*
* On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
* (PPro errata 66, 92)
*/
# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
#else
# define UNLOCK_LOCK_PREFIX
#endif
/*
* 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 __ticket_spin_lock(arch_spinlock_t *lock)
{
register struct __raw_tickets inc = { .tail = 1 };
inc = xadd(&lock->tickets, inc);
for (;;) {
if (inc.head == inc.tail)
break;
cpu_relax();
inc.head = ACCESS_ONCE(lock->tickets.head);
}
barrier(); /* make sure nothing creeps before the lock is taken */
}
static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
{
arch_spinlock_t old, new;
old.tickets = ACCESS_ONCE(lock->tickets);
if (old.tickets.head != old.tickets.tail)
return 0;
new.head_tail = old.head_tail + (1 << TICKET_SHIFT);
/* 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 __ticket_spin_unlock(arch_spinlock_t *lock)
{
__add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX);
}
static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
return tmp.tail != tmp.head;
}
static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
return (__ticket_t)(tmp.tail - tmp.head) > 1;
}
#ifndef CONFIG_PARAVIRT_SPINLOCKS
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
return __ticket_spin_is_locked(lock);
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
return __ticket_spin_is_contended(lock);
}
#define arch_spin_is_contended arch_spin_is_contended
static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
{
__ticket_spin_lock(lock);
}
static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
{
return __ticket_spin_trylock(lock);
}
static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
__ticket_spin_unlock(lock);
}
static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
unsigned long flags)
{
arch_spin_lock(lock);
}
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
while (arch_spin_is_locked(lock))
cpu_relax();
}
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
*
* NOTE! it is quite common to have readers in interrupts
* but no interrupt writers. For those circumstances we
* can "mix" irq-safe locks - any writer needs to get a
* irq-safe write-lock, but readers can get non-irqsafe
* read-locks.
*
* On x86, we implement read-write locks as a 32-bit counter
* with the high bit (sign) being the "contended" bit.
*/
/**
* read_can_lock - would read_trylock() succeed?
* @lock: the rwlock in question.
*/
static inline int arch_read_can_lock(arch_rwlock_t *lock)
{
return lock->lock > 0;
}
/**
* write_can_lock - would write_trylock() succeed?
* @lock: the rwlock in question.
*/
static inline int arch_write_can_lock(arch_rwlock_t *lock)
{
return lock->write == WRITE_LOCK_CMP;
}
static inline void arch_read_lock(arch_rwlock_t *rw)
{
asm volatile(LOCK_PREFIX READ_LOCK_SIZE(dec) " (%0)\n\t"
"jns 1f\n"
"call __read_lock_failed\n\t"
"1:\n"
::LOCK_PTR_REG (rw) : "memory");
}
static inline void arch_write_lock(arch_rwlock_t *rw)
{
asm volatile(LOCK_PREFIX WRITE_LOCK_SUB(%1) "(%0)\n\t"
"jz 1f\n"
"call __write_lock_failed\n\t"
"1:\n"
::LOCK_PTR_REG (&rw->write), "i" (RW_LOCK_BIAS)
: "memory");
}
static inline int arch_read_trylock(arch_rwlock_t *lock)
{
READ_LOCK_ATOMIC(t) *count = (READ_LOCK_ATOMIC(t) *)lock;
if (READ_LOCK_ATOMIC(dec_return)(count) >= 0)
return 1;
READ_LOCK_ATOMIC(inc)(count);
return 0;
}
static inline int arch_write_trylock(arch_rwlock_t *lock)
{
atomic_t *count = (atomic_t *)&lock->write;
if (atomic_sub_and_test(WRITE_LOCK_CMP, count))
return 1;
atomic_add(WRITE_LOCK_CMP, count);
return 0;
}
static inline void arch_read_unlock(arch_rwlock_t *rw)
{
asm volatile(LOCK_PREFIX READ_LOCK_SIZE(inc) " %0"
:"+m" (rw->lock) : : "memory");
}
static inline void arch_write_unlock(arch_rwlock_t *rw)
{
asm volatile(LOCK_PREFIX WRITE_LOCK_ADD(%1) "%0"
: "+m" (rw->write) : "i" (RW_LOCK_BIAS) : "memory");
}
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
#undef READ_LOCK_SIZE
#undef READ_LOCK_ATOMIC
#undef WRITE_LOCK_ADD
#undef WRITE_LOCK_SUB
#undef WRITE_LOCK_CMP
#define arch_spin_relax(lock) cpu_relax()
#define arch_read_relax(lock) cpu_relax()
#define arch_write_relax(lock) cpu_relax()
/* The {read|write|spin}_lock() on x86 are full memory barriers. */
static inline void smp_mb__after_lock(void) { }
#define ARCH_HAS_SMP_MB_AFTER_LOCK
#endif /* _ASM_X86_SPINLOCK_H */
