arch/x86/include/asm/spinlock.h - kernel/lockdown - Git at Google

 #ifndef _ASM_X86_SPINLOCK_H
 #define _ASM_X86_SPINLOCK_H

 #include <linux/jump_label.h>
 #include <linux/atomic.h>
 #include <asm/page.h>
 #include <asm/processor.h>
 #include <linux/compiler.h>
 #include <asm/paravirt.h>
 #include <asm/bitops.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 support up to 2^16 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_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_PARAVIRT_SPINLOCKS

 static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
 {
 	set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
 }

 #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 __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
 	return 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;

 	inc.tail &= ~TICKET_SLOWPATH_FLAG;
 	for (;;) {
 		unsigned count = SPIN_THRESHOLD;

 		do {
 			if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
 				goto out;
 			cpu_relax();
 		} while (--count);
 		__ticket_lock_spinning(lock, inc.tail);
 	}
 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 = ACCESS_ONCE(lock->tickets);
 	if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
 		return 0;

 	new.head_tail = old.head_tail + (TICKET_LOCK_INC << 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 inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
 					    arch_spinlock_t old)
 {
 	arch_spinlock_t new;

 	BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);

 	/* Perform the unlock on the "before" copy */
 	old.tickets.head += TICKET_LOCK_INC;

 	/* Clear the slowpath flag */
 	new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG << TICKET_SHIFT);

 	/*
 	 * If the lock is uncontended, clear the flag - use cmpxchg in
 	 * case it changes behind our back though.
 	 */
 	if (new.tickets.head != new.tickets.tail ||
 	    cmpxchg(&lock->head_tail, old.head_tail,
 					new.head_tail) != old.head_tail) {
 		/*
 		 * Lock still has someone queued for it, so wake up an
 		 * appropriate waiter.
 		 */
 		__ticket_unlock_kick(lock, old.tickets.head);
 	}
 }

 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
 	if (TICKET_SLOWPATH_FLAG &&
 	    static_key_false(&paravirt_ticketlocks_enabled)) {
 		arch_spinlock_t prev;

 		prev = *lock;
 		add_smp(&lock->tickets.head, TICKET_LOCK_INC);

 		/* add_smp() is a full mb() */

 		if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
 			__ticket_unlock_slowpath(lock, prev);
 	} 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 = ACCESS_ONCE(lock->tickets);

 	return tmp.tail != tmp.head;
 }

 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
 {
 	struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

 	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)
 {
 	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()

 #endif /* _ASM_X86_SPINLOCK_H */
	#ifndef _ASM_X86_SPINLOCK_H
	#define _ASM_X86_SPINLOCK_H

	#include <linux/jump_label.h>
	#include <linux/atomic.h>
	#include <asm/page.h>
	#include <asm/processor.h>
	#include <linux/compiler.h>
	#include <asm/paravirt.h>
	#include <asm/bitops.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 support up to 2^16 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_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_PARAVIRT_SPINLOCKS

	static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
	{
	set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
	}

	#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 __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
	{
	return 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;

	inc.tail &= ~TICKET_SLOWPATH_FLAG;
	for (;;) {
	unsigned count = SPIN_THRESHOLD;

	do {
	if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
	goto out;
	cpu_relax();
	} while (--count);
	__ticket_lock_spinning(lock, inc.tail);
	}
	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 = ACCESS_ONCE(lock->tickets);
	if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
	return 0;

	new.head_tail = old.head_tail + (TICKET_LOCK_INC << 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 inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
	arch_spinlock_t old)
	{
	arch_spinlock_t new;

	BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);

	/* Perform the unlock on the "before" copy */
	old.tickets.head += TICKET_LOCK_INC;

	/* Clear the slowpath flag */
	new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG << TICKET_SHIFT);

	/*
	* If the lock is uncontended, clear the flag - use cmpxchg in
	* case it changes behind our back though.
	*/
	if (new.tickets.head != new.tickets.tail \|\|
	cmpxchg(&lock->head_tail, old.head_tail,
	new.head_tail) != old.head_tail) {
	/*
	* Lock still has someone queued for it, so wake up an
	* appropriate waiter.
	*/
	__ticket_unlock_kick(lock, old.tickets.head);
	}
	}

	static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
	{
	if (TICKET_SLOWPATH_FLAG &&
	static_key_false(&paravirt_ticketlocks_enabled)) {
	arch_spinlock_t prev;

	prev = *lock;
	add_smp(&lock->tickets.head, TICKET_LOCK_INC);

	/* add_smp() is a full mb() */

	if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
	__ticket_unlock_slowpath(lock, prev);
	} 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 = ACCESS_ONCE(lock->tickets);

	return tmp.tail != tmp.head;
	}

	static inline int arch_spin_is_contended(arch_spinlock_t *lock)
	{
	struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

	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)
	{
	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()

	#endif /* _ASM_X86_SPINLOCK_H */