arch/x86/include/asm/spinlock.h

   1 #ifndef _ASM_X86_SPINLOCK_H
   2 #define _ASM_X86_SPINLOCK_H
   3
   4 #include <linux/atomic.h>
   5 #include <asm/page.h>
   6 #include <asm/processor.h>
   7 #include <linux/compiler.h>
   8 #include <asm/paravirt.h>
   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  * These are fair FIFO ticket locks, which are currently limited to 256
  16  * CPUs.
  17  *
  18  * (the type definitions are in asm/spinlock_types.h)
  19  */
  20
  21 #ifdef CONFIG_X86_32
  22 # define LOCK_PTR_REG "a"
  23 # define REG_PTR_MODE "k"
  24 #else
  25 # define LOCK_PTR_REG "D"
  26 # define REG_PTR_MODE "q"
  27 #endif
  28
  29 #if defined(CONFIG_X86_32) && \
  30         (defined(CONFIG_X86_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE))
  31 /*
  32  * On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
  33  * (PPro errata 66, 92)
  34  */
  35 static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
  36 {
  37         if (sizeof(lock->tickets.head) == sizeof(u8))
  38                 asm volatile(LOCK_PREFIX "incb %0"
  39                              : "+m" (lock->tickets.head) : : "memory");
  40         else
  41                 asm volatile(LOCK_PREFIX "incw %0"
  42                              : "+m" (lock->tickets.head) : : "memory");
  43
  44 }
  45 #else
  46 static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
  47 {
  48         lock->tickets.head++;
  49 }
  50 #endif
  51
  52 /*
  53  * Ticket locks are conceptually two parts, one indicating the current head of
  54  * the queue, and the other indicating the current tail. The lock is acquired
  55  * by atomically noting the tail and incrementing it by one (thus adding
  56  * ourself to the queue and noting our position), then waiting until the head
  57  * becomes equal to the the initial value of the tail.
  58  *
  59  * We use an xadd covering *both* parts of the lock, to increment the tail and
  60  * also load the position of the head, which takes care of memory ordering
  61  * issues and should be optimal for the uncontended case. Note the tail must be
  62  * in the high part, because a wide xadd increment of the low part would carry
  63  * up and contaminate the high part.
  64  *
  65  * With fewer than 2^8 possible CPUs, we can use x86's partial registers to
  66  * save some instructions and make the code more elegant. There really isn't
  67  * much between them in performance though, especially as locks are out of line.
  68  */
  69 static __always_inline struct __raw_tickets __ticket_spin_claim(struct arch_spinlock *lock)
  70 {
  71         register struct __raw_tickets tickets = { .tail = 1 };
  72
  73         xadd(&lock->tickets, tickets);
  74
  75         return tickets;
  76 }
  77
  78 static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
  79 {
  80         register struct __raw_tickets inc;
  81
  82         inc = __ticket_spin_claim(lock);
  83
  84         for (;;) {
  85                 if (inc.head == inc.tail)
  86                         goto out;
  87                 cpu_relax();
  88                 inc.head = ACCESS_ONCE(lock->tickets.head);
  89         }
  90 out:    barrier();              /* make sure nothing creeps before the lock is taken */
  91 }
  92
  93 static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
  94 {
  95         arch_spinlock_t old, new;
  96
  97         old.tickets = ACCESS_ONCE(lock->tickets);
  98         if (old.tickets.head != old.tickets.tail)
  99                 return 0;
 100
 101         new.head_tail = old.head_tail + (1 << TICKET_SHIFT);
 102
 103         /* cmpxchg is a full barrier, so nothing can move before it */
 104         return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
 105 }
 106
 107 static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
 108 {
 109         barrier();              /* prevent reordering out of locked region */
 110         __ticket_unlock_release(lock);
 111         barrier();              /* prevent reordering into locked region */
 112 }
 113
 114 static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
 115 {
 116         struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
 117
 118         return !!(tmp.tail ^ tmp.head);
 119 }
 120
 121 static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
 122 {
 123         struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
 124
 125         return ((tmp.tail - tmp.head) & TICKET_MASK) > 1;
 126 }
 127
 128 #ifndef CONFIG_PARAVIRT_SPINLOCKS
 129
 130 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
 131 {
 132         return __ticket_spin_is_locked(lock);
 133 }
 134
 135 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
 136 {
 137         return __ticket_spin_is_contended(lock);
 138 }
 139 #define arch_spin_is_contended  arch_spin_is_contended
 140
 141 static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
 142 {
 143         __ticket_spin_lock(lock);
 144 }
 145
 146 static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
 147 {
 148         return __ticket_spin_trylock(lock);
 149 }
 150
 151 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 152 {
 153         __ticket_spin_unlock(lock);
 154 }
 155
 156 static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
 157                                                   unsigned long flags)
 158 {
 159         arch_spin_lock(lock);
 160 }
 161
 162 #endif  /* CONFIG_PARAVIRT_SPINLOCKS */
 163
 164 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 165 {
 166         while (arch_spin_is_locked(lock))
 167                 cpu_relax();
 168 }
 169
 170 /*
 171  * Read-write spinlocks, allowing multiple readers
 172  * but only one writer.
 173  *
 174  * NOTE! it is quite common to have readers in interrupts
 175  * but no interrupt writers. For those circumstances we
 176  * can "mix" irq-safe locks - any writer needs to get a
 177  * irq-safe write-lock, but readers can get non-irqsafe
 178  * read-locks.
 179  *
 180  * On x86, we implement read-write locks as a 32-bit counter
 181  * with the high bit (sign) being the "contended" bit.
 182  */
 183
 184 /**
 185  * read_can_lock - would read_trylock() succeed?
 186  * @lock: the rwlock in question.
 187  */
 188 static inline int arch_read_can_lock(arch_rwlock_t *lock)
 189 {
 190         return lock->lock > 0;
 191 }
 192
 193 /**
 194  * write_can_lock - would write_trylock() succeed?
 195  * @lock: the rwlock in question.
 196  */
 197 static inline int arch_write_can_lock(arch_rwlock_t *lock)
 198 {
 199         return lock->write == WRITE_LOCK_CMP;
 200 }
 201
 202 static inline void arch_read_lock(arch_rwlock_t *rw)
 203 {
 204         asm volatile(LOCK_PREFIX READ_LOCK_SIZE(dec) " (%0)\n\t"
 205                      "jns 1f\n"
 206                      "call __read_lock_failed\n\t"
 207                      "1:\n"
 208                      ::LOCK_PTR_REG (rw) : "memory");
 209 }
 210
 211 static inline void arch_write_lock(arch_rwlock_t *rw)
 212 {
 213         asm volatile(LOCK_PREFIX WRITE_LOCK_SUB(%1) "(%0)\n\t"
 214                      "jz 1f\n"
 215                      "call __write_lock_failed\n\t"
 216                      "1:\n"
 217                      ::LOCK_PTR_REG (&rw->write), "i" (RW_LOCK_BIAS)
 218                      : "memory");
 219 }
 220
 221 static inline int arch_read_trylock(arch_rwlock_t *lock)
 222 {
 223         READ_LOCK_ATOMIC(t) *count = (READ_LOCK_ATOMIC(t) *)lock;
 224
 225         if (READ_LOCK_ATOMIC(dec_return)(count) >= 0)
 226                 return 1;
 227         READ_LOCK_ATOMIC(inc)(count);
 228         return 0;
 229 }
 230
 231 static inline int arch_write_trylock(arch_rwlock_t *lock)
 232 {
 233         atomic_t *count = (atomic_t *)&lock->write;
 234
 235         if (atomic_sub_and_test(WRITE_LOCK_CMP, count))
 236                 return 1;
 237         atomic_add(WRITE_LOCK_CMP, count);
 238         return 0;
 239 }
 240
 241 static inline void arch_read_unlock(arch_rwlock_t *rw)
 242 {
 243         asm volatile(LOCK_PREFIX READ_LOCK_SIZE(inc) " %0"
 244                      :"+m" (rw->lock) : : "memory");
 245 }
 246
 247 static inline void arch_write_unlock(arch_rwlock_t *rw)
 248 {
 249         asm volatile(LOCK_PREFIX WRITE_LOCK_ADD(%1) "%0"
 250                      : "+m" (rw->write) : "i" (RW_LOCK_BIAS) : "memory");
 251 }
 252
 253 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 254 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 255
 256 #undef READ_LOCK_SIZE
 257 #undef READ_LOCK_ATOMIC
 258 #undef WRITE_LOCK_ADD
 259 #undef WRITE_LOCK_SUB
 260 #undef WRITE_LOCK_CMP
 261
 262 #define arch_spin_relax(lock)   cpu_relax()
 263 #define arch_read_relax(lock)   cpu_relax()
 264 #define arch_write_relax(lock)  cpu_relax()
 265
 266 /* The {read|write|spin}_lock() on x86 are full memory barriers. */
 267 static inline void smp_mb__after_lock(void) { }
 268 #define ARCH_HAS_SMP_MB_AFTER_LOCK
 269
 270 #endif /* _ASM_X86_SPINLOCK_H */