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

 #ifndef _ASM_X86_SPINLOCK_H
 #define _ASM_X86_SPINLOCK_H

 #include <asm/atomic.h>
 #include <asm/rwlock.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"
 # define REG_PTR_MODE "k"
 #else
 # define LOCK_PTR_REG "D"
 # define REG_PTR_MODE "q"
 #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.
  *
  * With fewer than 2^8 possible CPUs, we can use x86's partial registers to
  * save some instructions and make the code more elegant. There really isn't
  * much between them in performance though, especially as locks are out of line.
  */
 #if (NR_CPUS < 256)
 #define TICKET_SHIFT 8

 static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
 {
 	short inc = 0x0100;

 	asm volatile (
 		LOCK_PREFIX "xaddw %w0, %1\n"
 		"1:\t"
 		"cmpb %h0, %b0\n\t"
 		"je 2f\n\t"
 		"rep ; nop\n\t"
 		"movb %1, %b0\n\t"
 		/* don't need lfence here, because loads are in-order */
 		"jmp 1b\n"
 		"2:"
 		: "+Q" (inc), "+m" (lock->slock)
 		:
 		: "memory", "cc");
 }

 static __always_inline int __ticket_spin_trylock(raw_spinlock_t *lock)
 {
 	int tmp, new;

 	asm volatile("movzwl %2, %0\n\t"
 		     "cmpb %h0,%b0\n\t"
 		     "leal 0x100(%" REG_PTR_MODE "0), %1\n\t"
 		     "jne 1f\n\t"
 		     LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
 		     "1:"
 		     "sete %b1\n\t"
 		     "movzbl %b1,%0\n\t"
 		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
 		     :
 		     : "memory", "cc");

 	return tmp;
 }

 static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
 {
 	asm volatile(UNLOCK_LOCK_PREFIX "incb %0"
 		     : "+m" (lock->slock)
 		     :
 		     : "memory", "cc");
 }
 #else
 #define TICKET_SHIFT 16

 static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
 {
 	int inc = 0x00010000;
 	int tmp;

 	asm volatile(LOCK_PREFIX "xaddl %0, %1\n"
 		     "movzwl %w0, %2\n\t"
 		     "shrl $16, %0\n\t"
 		     "1:\t"
 		     "cmpl %0, %2\n\t"
 		     "je 2f\n\t"
 		     "rep ; nop\n\t"
 		     "movzwl %1, %2\n\t"
 		     /* don't need lfence here, because loads are in-order */
 		     "jmp 1b\n"
 		     "2:"
 		     : "+r" (inc), "+m" (lock->slock), "=&r" (tmp)
 		     :
 		     : "memory", "cc");
 }

 static __always_inline int __ticket_spin_trylock(raw_spinlock_t *lock)
 {
 	int tmp;
 	int new;

 	asm volatile("movl %2,%0\n\t"
 		     "movl %0,%1\n\t"
 		     "roll $16, %0\n\t"
 		     "cmpl %0,%1\n\t"
 		     "leal 0x00010000(%" REG_PTR_MODE "0), %1\n\t"
 		     "jne 1f\n\t"
 		     LOCK_PREFIX "cmpxchgl %1,%2\n\t"
 		     "1:"
 		     "sete %b1\n\t"
 		     "movzbl %b1,%0\n\t"
 		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
 		     :
 		     : "memory", "cc");

 	return tmp;
 }

 static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
 {
 	asm volatile(UNLOCK_LOCK_PREFIX "incw %0"
 		     : "+m" (lock->slock)
 		     :
 		     : "memory", "cc");
 }
 #endif

 static inline int __ticket_spin_is_locked(raw_spinlock_t *lock)
 {
 	int tmp = ACCESS_ONCE(lock->slock);

 	return !!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1 << TICKET_SHIFT) - 1));
 }

 static inline int __ticket_spin_is_contended(raw_spinlock_t *lock)
 {
 	int tmp = ACCESS_ONCE(lock->slock);

 	return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
 }

 #ifndef CONFIG_PARAVIRT_SPINLOCKS

 static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
 {
 	return __ticket_spin_is_locked(lock);
 }

 static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
 {
 	return __ticket_spin_is_contended(lock);
 }
 #define __raw_spin_is_contended	__raw_spin_is_contended

 static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)
 {
 	__ticket_spin_lock(lock);
 }

 static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)
 {
 	return __ticket_spin_trylock(lock);
 }

 static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)
 {
 	__ticket_spin_unlock(lock);
 }

 static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
 						  unsigned long flags)
 {
 	__raw_spin_lock(lock);
 }

 #endif	/* CONFIG_PARAVIRT_SPINLOCKS */

 static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
 {
 	while (__raw_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 __raw_read_can_lock(raw_rwlock_t *lock)
 {
 	return (int)(lock)->lock > 0;
 }

 /**
  * write_can_lock - would write_trylock() succeed?
  * @lock: the rwlock in question.
  */
 static inline int __raw_write_can_lock(raw_rwlock_t *lock)
 {
 	return (lock)->lock == RW_LOCK_BIAS;
 }

 static inline void __raw_read_lock(raw_rwlock_t *rw)
 {
 	asm volatile(LOCK_PREFIX " subl $1,(%0)\n\t"
 		     "jns 1f\n"
 		     "call __read_lock_failed\n\t"
 		     "1:\n"
 		     ::LOCK_PTR_REG (rw) : "memory");
 }

 static inline void __raw_write_lock(raw_rwlock_t *rw)
 {
 	asm volatile(LOCK_PREFIX " subl %1,(%0)\n\t"
 		     "jz 1f\n"
 		     "call __write_lock_failed\n\t"
 		     "1:\n"
 		     ::LOCK_PTR_REG (rw), "i" (RW_LOCK_BIAS) : "memory");
 }

 static inline int __raw_read_trylock(raw_rwlock_t *lock)
 {
 	atomic_t *count = (atomic_t *)lock;

 	if (atomic_dec_return(count) >= 0)
 		return 1;
 	atomic_inc(count);
 	return 0;
 }

 static inline int __raw_write_trylock(raw_rwlock_t *lock)
 {
 	atomic_t *count = (atomic_t *)lock;

 	if (atomic_sub_and_test(RW_LOCK_BIAS, count))
 		return 1;
 	atomic_add(RW_LOCK_BIAS, count);
 	return 0;
 }

 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 {
 	asm volatile(LOCK_PREFIX "incl %0" :"+m" (rw->lock) : : "memory");
 }

 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 {
 	asm volatile(LOCK_PREFIX "addl %1, %0"
 		     : "+m" (rw->lock) : "i" (RW_LOCK_BIAS) : "memory");
 }

 #define __raw_read_lock_flags(lock, flags) __raw_read_lock(lock)
 #define __raw_write_lock_flags(lock, flags) __raw_write_lock(lock)

 #define _raw_spin_relax(lock)	cpu_relax()
 #define _raw_read_relax(lock)	cpu_relax()
 #define _raw_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 */
	#ifndef _ASM_X86_SPINLOCK_H
	#define _ASM_X86_SPINLOCK_H

	#include <asm/atomic.h>
	#include <asm/rwlock.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"
	# define REG_PTR_MODE "k"
	#else
	# define LOCK_PTR_REG "D"
	# define REG_PTR_MODE "q"
	#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.
	*
	* With fewer than 2^8 possible CPUs, we can use x86's partial registers to
	* save some instructions and make the code more elegant. There really isn't
	* much between them in performance though, especially as locks are out of line.
	*/
	#if (NR_CPUS < 256)
	#define TICKET_SHIFT 8

	static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
	{
	short inc = 0x0100;

	asm volatile (
	LOCK_PREFIX "xaddw %w0, %1\n"
	"1:\t"
	"cmpb %h0, %b0\n\t"
	"je 2f\n\t"
	"rep ; nop\n\t"
	"movb %1, %b0\n\t"
	/* don't need lfence here, because loads are in-order */
	"jmp 1b\n"
	"2:"
	: "+Q" (inc), "+m" (lock->slock)
	:
	: "memory", "cc");
	}

	static __always_inline int __ticket_spin_trylock(raw_spinlock_t *lock)
	{
	int tmp, new;

	asm volatile("movzwl %2, %0\n\t"
	"cmpb %h0,%b0\n\t"
	"leal 0x100(%" REG_PTR_MODE "0), %1\n\t"
	"jne 1f\n\t"
	LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
	"1:"
	"sete %b1\n\t"
	"movzbl %b1,%0\n\t"
	: "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
	:
	: "memory", "cc");

	return tmp;
	}

	static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
	{
	asm volatile(UNLOCK_LOCK_PREFIX "incb %0"
	: "+m" (lock->slock)
	:
	: "memory", "cc");
	}
	#else
	#define TICKET_SHIFT 16

	static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
	{
	int inc = 0x00010000;
	int tmp;

	asm volatile(LOCK_PREFIX "xaddl %0, %1\n"
	"movzwl %w0, %2\n\t"
	"shrl $16, %0\n\t"
	"1:\t"
	"cmpl %0, %2\n\t"
	"je 2f\n\t"
	"rep ; nop\n\t"
	"movzwl %1, %2\n\t"
	/* don't need lfence here, because loads are in-order */
	"jmp 1b\n"
	"2:"
	: "+r" (inc), "+m" (lock->slock), "=&r" (tmp)
	:
	: "memory", "cc");
	}

	static __always_inline int __ticket_spin_trylock(raw_spinlock_t *lock)
	{
	int tmp;
	int new;

	asm volatile("movl %2,%0\n\t"
	"movl %0,%1\n\t"
	"roll $16, %0\n\t"
	"cmpl %0,%1\n\t"
	"leal 0x00010000(%" REG_PTR_MODE "0), %1\n\t"
	"jne 1f\n\t"
	LOCK_PREFIX "cmpxchgl %1,%2\n\t"
	"1:"
	"sete %b1\n\t"
	"movzbl %b1,%0\n\t"
	: "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
	:
	: "memory", "cc");

	return tmp;
	}

	static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
	{
	asm volatile(UNLOCK_LOCK_PREFIX "incw %0"
	: "+m" (lock->slock)
	:
	: "memory", "cc");
	}
	#endif

	static inline int __ticket_spin_is_locked(raw_spinlock_t *lock)
	{
	int tmp = ACCESS_ONCE(lock->slock);

	return !!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1 << TICKET_SHIFT) - 1));
	}

	static inline int __ticket_spin_is_contended(raw_spinlock_t *lock)
	{
	int tmp = ACCESS_ONCE(lock->slock);

	return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
	}

	#ifndef CONFIG_PARAVIRT_SPINLOCKS

	static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
	{
	return __ticket_spin_is_locked(lock);
	}

	static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
	{
	return __ticket_spin_is_contended(lock);
	}
	#define __raw_spin_is_contended __raw_spin_is_contended

	static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)
	{
	__ticket_spin_lock(lock);
	}

	static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)
	{
	return __ticket_spin_trylock(lock);
	}

	static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)
	{
	__ticket_spin_unlock(lock);
	}

	static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
	unsigned long flags)
	{
	__raw_spin_lock(lock);
	}

	#endif /* CONFIG_PARAVIRT_SPINLOCKS */

	static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
	{
	while (__raw_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 __raw_read_can_lock(raw_rwlock_t *lock)
	{
	return (int)(lock)->lock > 0;
	}

	/**
	* write_can_lock - would write_trylock() succeed?
	* @lock: the rwlock in question.
	*/
	static inline int __raw_write_can_lock(raw_rwlock_t *lock)
	{
	return (lock)->lock == RW_LOCK_BIAS;
	}

	static inline void __raw_read_lock(raw_rwlock_t *rw)
	{
	asm volatile(LOCK_PREFIX " subl $1,(%0)\n\t"
	"jns 1f\n"
	"call __read_lock_failed\n\t"
	"1:\n"
	::LOCK_PTR_REG (rw) : "memory");
	}

	static inline void __raw_write_lock(raw_rwlock_t *rw)
	{
	asm volatile(LOCK_PREFIX " subl %1,(%0)\n\t"
	"jz 1f\n"
	"call __write_lock_failed\n\t"
	"1:\n"
	::LOCK_PTR_REG (rw), "i" (RW_LOCK_BIAS) : "memory");
	}

	static inline int __raw_read_trylock(raw_rwlock_t *lock)
	{
	atomic_t count = (atomic_t )lock;

	if (atomic_dec_return(count) >= 0)
	return 1;
	atomic_inc(count);
	return 0;
	}

	static inline int __raw_write_trylock(raw_rwlock_t *lock)
	{
	atomic_t count = (atomic_t )lock;

	if (atomic_sub_and_test(RW_LOCK_BIAS, count))
	return 1;
	atomic_add(RW_LOCK_BIAS, count);
	return 0;
	}

	static inline void __raw_read_unlock(raw_rwlock_t *rw)
	{
	asm volatile(LOCK_PREFIX "incl %0" :"+m" (rw->lock) : : "memory");
	}

	static inline void __raw_write_unlock(raw_rwlock_t *rw)
	{
	asm volatile(LOCK_PREFIX "addl %1, %0"
	: "+m" (rw->lock) : "i" (RW_LOCK_BIAS) : "memory");
	}

	#define __raw_read_lock_flags(lock, flags) __raw_read_lock(lock)
	#define __raw_write_lock_flags(lock, flags) __raw_write_lock(lock)

	#define _raw_spin_relax(lock) cpu_relax()
	#define _raw_read_relax(lock) cpu_relax()
	#define _raw_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 */