include/asm-i386/spinlock.h

   1 #ifndef __ASM_SPINLOCK_H
   2 #define __ASM_SPINLOCK_H
   3
   4 #include <asm/atomic.h>
   5 #include <asm/rwlock.h>
   6 #include <asm/page.h>
   7 #include <linux/compiler.h>
   8
   9 /*
  10  * Your basic SMP spinlocks, allowing only a single CPU anywhere
  11  *
  12  * Simple spin lock operations.  There are two variants, one clears IRQ's
  13  * on the local processor, one does not.
  14  *
  15  * We make no fairness assumptions. They have a cost.
  16  *
  17  * (the type definitions are in asm/spinlock_types.h)
  18  */
  19
  20 #define __raw_spin_is_locked(x) \
  21                 (*(volatile signed char *)(&(x)->slock) <= 0)
  22
  23 #define __raw_spin_lock_string \
  24         "\n1:\t" \
  25         LOCK_PREFIX " ; decb %0\n\t" \
  26         "jns 3f\n" \
  27         "2:\t" \
  28         "rep;nop\n\t" \
  29         "cmpb $0,%0\n\t" \
  30         "jle 2b\n\t" \
  31         "jmp 1b\n" \
  32         "3:\n\t"
  33
  34 /*
  35  * NOTE: there's an irqs-on section here, which normally would have to be
  36  * irq-traced, but on CONFIG_TRACE_IRQFLAGS we never use
  37  * __raw_spin_lock_string_flags().
  38  */
  39 #define __raw_spin_lock_string_flags \
  40         "\n1:\t" \
  41         LOCK_PREFIX " ; decb %0\n\t" \
  42         "jns 5f\n" \
  43         "2:\t" \
  44         "testl $0x200, %1\n\t" \
  45         "jz 4f\n\t" \
  46         "sti\n" \
  47         "3:\t" \
  48         "rep;nop\n\t" \
  49         "cmpb $0, %0\n\t" \
  50         "jle 3b\n\t" \
  51         "cli\n\t" \
  52         "jmp 1b\n" \
  53         "4:\t" \
  54         "rep;nop\n\t" \
  55         "cmpb $0, %0\n\t" \
  56         "jg 1b\n\t" \
  57         "jmp 4b\n" \
  58         "5:\n\t"
  59
  60 static inline void __raw_spin_lock(raw_spinlock_t *lock)
  61 {
  62         asm(__raw_spin_lock_string : "+m" (lock->slock) : : "memory");
  63 }
  64
  65 /*
  66  * It is easier for the lock validator if interrupts are not re-enabled
  67  * in the middle of a lock-acquire. This is a performance feature anyway
  68  * so we turn it off:
  69  */
  70 #ifndef CONFIG_PROVE_LOCKING
  71 static inline void __raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long flags)
  72 {
  73         asm(__raw_spin_lock_string_flags : "+m" (lock->slock) : "r" (flags) : "memory");
  74 }
  75 #endif
  76
  77 static inline int __raw_spin_trylock(raw_spinlock_t *lock)
  78 {
  79         char oldval;
  80         __asm__ __volatile__(
  81                 "xchgb %b0,%1"
  82                 :"=q" (oldval), "+m" (lock->slock)
  83                 :"0" (0) : "memory");
  84         return oldval > 0;
  85 }
  86
  87 /*
  88  * __raw_spin_unlock based on writing $1 to the low byte.
  89  * This method works. Despite all the confusion.
  90  * (except on PPro SMP or if we are using OOSTORE, so we use xchgb there)
  91  * (PPro errata 66, 92)
  92  */
  93
  94 #if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE)
  95
  96 #define __raw_spin_unlock_string \
  97         "movb $1,%0" \
  98                 :"+m" (lock->slock) : : "memory"
  99
 100
 101 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 102 {
 103         __asm__ __volatile__(
 104                 __raw_spin_unlock_string
 105         );
 106 }
 107
 108 #else
 109
 110 #define __raw_spin_unlock_string \
 111         "xchgb %b0, %1" \
 112                 :"=q" (oldval), "+m" (lock->slock) \
 113                 :"0" (oldval) : "memory"
 114
 115 static inline void __raw_spin_unlock(raw_spinlock_t *lock)
 116 {
 117         char oldval = 1;
 118
 119         __asm__ __volatile__(
 120                 __raw_spin_unlock_string
 121         );
 122 }
 123
 124 #endif
 125
 126 #define __raw_spin_unlock_wait(lock) \
 127         do { while (__raw_spin_is_locked(lock)) cpu_relax(); } while (0)
 128
 129 /*
 130  * Read-write spinlocks, allowing multiple readers
 131  * but only one writer.
 132  *
 133  * NOTE! it is quite common to have readers in interrupts
 134  * but no interrupt writers. For those circumstances we
 135  * can "mix" irq-safe locks - any writer needs to get a
 136  * irq-safe write-lock, but readers can get non-irqsafe
 137  * read-locks.
 138  *
 139  * On x86, we implement read-write locks as a 32-bit counter
 140  * with the high bit (sign) being the "contended" bit.
 141  *
 142  * The inline assembly is non-obvious. Think about it.
 143  *
 144  * Changed to use the same technique as rw semaphores.  See
 145  * semaphore.h for details.  -ben
 146  *
 147  * the helpers are in arch/i386/kernel/semaphore.c
 148  */
 149
 150 /**
 151  * read_can_lock - would read_trylock() succeed?
 152  * @lock: the rwlock in question.
 153  */
 154 #define __raw_read_can_lock(x)          ((int)(x)->lock > 0)
 155
 156 /**
 157  * write_can_lock - would write_trylock() succeed?
 158  * @lock: the rwlock in question.
 159  */
 160 #define __raw_write_can_lock(x)         ((x)->lock == RW_LOCK_BIAS)
 161
 162 static inline void __raw_read_lock(raw_rwlock_t *rw)
 163 {
 164         __build_read_lock(rw, "__read_lock_failed");
 165 }
 166
 167 static inline void __raw_write_lock(raw_rwlock_t *rw)
 168 {
 169         __build_write_lock(rw, "__write_lock_failed");
 170 }
 171
 172 static inline int __raw_read_trylock(raw_rwlock_t *lock)
 173 {
 174         atomic_t *count = (atomic_t *)lock;
 175         atomic_dec(count);
 176         if (atomic_read(count) >= 0)
 177                 return 1;
 178         atomic_inc(count);
 179         return 0;
 180 }
 181
 182 static inline int __raw_write_trylock(raw_rwlock_t *lock)
 183 {
 184         atomic_t *count = (atomic_t *)lock;
 185         if (atomic_sub_and_test(RW_LOCK_BIAS, count))
 186                 return 1;
 187         atomic_add(RW_LOCK_BIAS, count);
 188         return 0;
 189 }
 190
 191 static inline void __raw_read_unlock(raw_rwlock_t *rw)
 192 {
 193         asm volatile(LOCK_PREFIX "incl %0" :"+m" (rw->lock) : : "memory");
 194 }
 195
 196 static inline void __raw_write_unlock(raw_rwlock_t *rw)
 197 {
 198         asm volatile(LOCK_PREFIX "addl $" RW_LOCK_BIAS_STR ", %0"
 199                                  : "+m" (rw->lock) : : "memory");
 200 }
 201
 202 #endif /* __ASM_SPINLOCK_H */