include/linux/spinlock.h

   1 #ifndef __LINUX_SPINLOCK_H
   2 #define __LINUX_SPINLOCK_H
   3
   4 /*
   5  * include/linux/spinlock.h - generic locking declarations
   6  */
   7
   8 #include <linux/config.h>
   9 #include <linux/preempt.h>
  10 #include <linux/linkage.h>
  11 #include <linux/compiler.h>
  12 #include <linux/thread_info.h>
  13 #include <linux/kernel.h>
  14 #include <linux/stringify.h>
  15
  16 #include <asm/processor.h>      /* for cpu relax */
  17 #include <asm/system.h>
  18
  19 /*
  20  * Must define these before including other files, inline functions need them
  21  */
  22 #define LOCK_SECTION_NAME                       \
  23         ".text.lock." __stringify(KBUILD_BASENAME)
  24
  25 #define LOCK_SECTION_START(extra)               \
  26         ".subsection 1\n\t"                     \
  27         extra                                   \
  28         ".ifndef " LOCK_SECTION_NAME "\n\t"     \
  29         LOCK_SECTION_NAME ":\n\t"               \
  30         ".endif\n"
  31
  32 #define LOCK_SECTION_END                        \
  33         ".previous\n\t"
  34
  35 #define __lockfunc fastcall __attribute__((section(".spinlock.text")))
  36
  37 /*
  38  * If CONFIG_SMP is set, pull in the _raw_* definitions
  39  */
  40 #ifdef CONFIG_SMP
  41
  42 #define assert_spin_locked(x)   BUG_ON(!spin_is_locked(x))
  43 #include <asm/spinlock.h>
  44
  45 int __lockfunc _spin_trylock(spinlock_t *lock);
  46 int __lockfunc _read_trylock(rwlock_t *lock);
  47 int __lockfunc _write_trylock(rwlock_t *lock);
  48
  49 void __lockfunc _spin_lock(spinlock_t *lock)    __acquires(spinlock_t);
  50 void __lockfunc _read_lock(rwlock_t *lock)      __acquires(rwlock_t);
  51 void __lockfunc _write_lock(rwlock_t *lock)     __acquires(rwlock_t);
  52
  53 void __lockfunc _spin_unlock(spinlock_t *lock)  __releases(spinlock_t);
  54 void __lockfunc _read_unlock(rwlock_t *lock)    __releases(rwlock_t);
  55 void __lockfunc _write_unlock(rwlock_t *lock)   __releases(rwlock_t);
  56
  57 unsigned long __lockfunc _spin_lock_irqsave(spinlock_t *lock)   __acquires(spinlock_t);
  58 unsigned long __lockfunc _read_lock_irqsave(rwlock_t *lock)     __acquires(rwlock_t);
  59 unsigned long __lockfunc _write_lock_irqsave(rwlock_t *lock)    __acquires(rwlock_t);
  60
  61 void __lockfunc _spin_lock_irq(spinlock_t *lock)        __acquires(spinlock_t);
  62 void __lockfunc _spin_lock_bh(spinlock_t *lock)         __acquires(spinlock_t);
  63 void __lockfunc _read_lock_irq(rwlock_t *lock)          __acquires(rwlock_t);
  64 void __lockfunc _read_lock_bh(rwlock_t *lock)           __acquires(rwlock_t);
  65 void __lockfunc _write_lock_irq(rwlock_t *lock)         __acquires(rwlock_t);
  66 void __lockfunc _write_lock_bh(rwlock_t *lock)          __acquires(rwlock_t);
  67
  68 void __lockfunc _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)  __releases(spinlock_t);
  69 void __lockfunc _spin_unlock_irq(spinlock_t *lock)                              __releases(spinlock_t);
  70 void __lockfunc _spin_unlock_bh(spinlock_t *lock)                               __releases(spinlock_t);
  71 void __lockfunc _read_unlock_irqrestore(rwlock_t *lock, unsigned long flags)    __releases(rwlock_t);
  72 void __lockfunc _read_unlock_irq(rwlock_t *lock)                                __releases(rwlock_t);
  73 void __lockfunc _read_unlock_bh(rwlock_t *lock)                                 __releases(rwlock_t);
  74 void __lockfunc _write_unlock_irqrestore(rwlock_t *lock, unsigned long flags)   __releases(rwlock_t);
  75 void __lockfunc _write_unlock_irq(rwlock_t *lock)                               __releases(rwlock_t);
  76 void __lockfunc _write_unlock_bh(rwlock_t *lock)                                __releases(rwlock_t);
  77
  78 int __lockfunc _spin_trylock_bh(spinlock_t *lock);
  79 int __lockfunc generic_raw_read_trylock(rwlock_t *lock);
  80 int in_lock_functions(unsigned long addr);
  81
  82 #else
  83
  84 #define in_lock_functions(ADDR) 0
  85
  86 #if !defined(CONFIG_PREEMPT) && !defined(CONFIG_DEBUG_SPINLOCK)
  87 # define _atomic_dec_and_lock(atomic,lock) atomic_dec_and_test(atomic)
  88 # define ATOMIC_DEC_AND_LOCK
  89 #endif
  90
  91 #ifdef CONFIG_DEBUG_SPINLOCK
  92
  93 #define SPINLOCK_MAGIC  0x1D244B3C
  94 typedef struct {
  95         unsigned long magic;
  96         volatile unsigned long lock;
  97         volatile unsigned int babble;
  98         const char *module;
  99         char *owner;
 100         int oline;
 101 } spinlock_t;
 102 #define SPIN_LOCK_UNLOCKED (spinlock_t) { SPINLOCK_MAGIC, 0, 10, __FILE__ , NULL, 0}
 103
 104 #define spin_lock_init(x) \
 105         do { \
 106                 (x)->magic = SPINLOCK_MAGIC; \
 107                 (x)->lock = 0; \
 108                 (x)->babble = 5; \
 109                 (x)->module = __FILE__; \
 110                 (x)->owner = NULL; \
 111                 (x)->oline = 0; \
 112         } while (0)
 113
 114 #define CHECK_LOCK(x) \
 115         do { \
 116                 if ((x)->magic != SPINLOCK_MAGIC) { \
 117                         printk(KERN_ERR "%s:%d: spin_is_locked on uninitialized spinlock %p.\n", \
 118                                         __FILE__, __LINE__, (x)); \
 119                 } \
 120         } while(0)
 121
 122 #define _raw_spin_lock(x)               \
 123         do { \
 124                 CHECK_LOCK(x); \
 125                 if ((x)->lock&&(x)->babble) { \
 126                         (x)->babble--; \
 127                         printk("%s:%d: spin_lock(%s:%p) already locked by %s/%d\n", \
 128                                         __FILE__,__LINE__, (x)->module, \
 129                                         (x), (x)->owner, (x)->oline); \
 130                 } \
 131                 (x)->lock = 1; \
 132                 (x)->owner = __FILE__; \
 133                 (x)->oline = __LINE__; \
 134         } while (0)
 135
 136 /* without debugging, spin_is_locked on UP always says
 137  * FALSE. --> printk if already locked. */
 138 #define spin_is_locked(x) \
 139         ({ \
 140                 CHECK_LOCK(x); \
 141                 if ((x)->lock&&(x)->babble) { \
 142                         (x)->babble--; \
 143                         printk("%s:%d: spin_is_locked(%s:%p) already locked by %s/%d\n", \
 144                                         __FILE__,__LINE__, (x)->module, \
 145                                         (x), (x)->owner, (x)->oline); \
 146                 } \
 147                 0; \
 148         })
 149
 150 /* with debugging, assert_spin_locked() on UP does check
 151  * the lock value properly */
 152 #define assert_spin_locked(x) \
 153         ({ \
 154                 CHECK_LOCK(x); \
 155                 BUG_ON(!(x)->lock); \
 156         })
 157
 158 /* without debugging, spin_trylock on UP always says
 159  * TRUE. --> printk if already locked. */
 160 #define _raw_spin_trylock(x) \
 161         ({ \
 162                 CHECK_LOCK(x); \
 163                 if ((x)->lock&&(x)->babble) { \
 164                         (x)->babble--; \
 165                         printk("%s:%d: spin_trylock(%s:%p) already locked by %s/%d\n", \
 166                                         __FILE__,__LINE__, (x)->module, \
 167                                         (x), (x)->owner, (x)->oline); \
 168                 } \
 169                 (x)->lock = 1; \
 170                 (x)->owner = __FILE__; \
 171                 (x)->oline = __LINE__; \
 172                 1; \
 173         })
 174
 175 #define spin_unlock_wait(x)     \
 176         do { \
 177                 CHECK_LOCK(x); \
 178                 if ((x)->lock&&(x)->babble) { \
 179                         (x)->babble--; \
 180                         printk("%s:%d: spin_unlock_wait(%s:%p) owned by %s/%d\n", \
 181                                         __FILE__,__LINE__, (x)->module, (x), \
 182                                         (x)->owner, (x)->oline); \
 183                 }\
 184         } while (0)
 185
 186 #define _raw_spin_unlock(x) \
 187         do { \
 188                 CHECK_LOCK(x); \
 189                 if (!(x)->lock&&(x)->babble) { \
 190                         (x)->babble--; \
 191                         printk("%s:%d: spin_unlock(%s:%p) not locked\n", \
 192                                         __FILE__,__LINE__, (x)->module, (x));\
 193                 } \
 194                 (x)->lock = 0; \
 195         } while (0)
 196 #else
 197 /*
 198  * gcc versions before ~2.95 have a nasty bug with empty initializers.
 199  */
 200 #if (__GNUC__ > 2)
 201   typedef struct { } spinlock_t;
 202   #define SPIN_LOCK_UNLOCKED (spinlock_t) { }
 203 #else
 204   typedef struct { int gcc_is_buggy; } spinlock_t;
 205   #define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 }
 206 #endif
 207
 208 /*
 209  * If CONFIG_SMP is unset, declare the _raw_* definitions as nops
 210  */
 211 #define spin_lock_init(lock)    do { (void)(lock); } while(0)
 212 #define _raw_spin_lock(lock)    do { (void)(lock); } while(0)
 213 #define spin_is_locked(lock)    ((void)(lock), 0)
 214 #define assert_spin_locked(lock)        do { (void)(lock); } while(0)
 215 #define _raw_spin_trylock(lock) (((void)(lock), 1))
 216 #define spin_unlock_wait(lock)  (void)(lock)
 217 #define _raw_spin_unlock(lock) do { (void)(lock); } while(0)
 218 #endif /* CONFIG_DEBUG_SPINLOCK */
 219
 220 /* RW spinlocks: No debug version */
 221
 222 #if (__GNUC__ > 2)
 223   typedef struct { } rwlock_t;
 224   #define RW_LOCK_UNLOCKED (rwlock_t) { }
 225 #else
 226   typedef struct { int gcc_is_buggy; } rwlock_t;
 227   #define RW_LOCK_UNLOCKED (rwlock_t) { 0 }
 228 #endif
 229
 230 #define rwlock_init(lock)       do { (void)(lock); } while(0)
 231 #define _raw_read_lock(lock)    do { (void)(lock); } while(0)
 232 #define _raw_read_unlock(lock)  do { (void)(lock); } while(0)
 233 #define _raw_write_lock(lock)   do { (void)(lock); } while(0)
 234 #define _raw_write_unlock(lock) do { (void)(lock); } while(0)
 235 #define read_can_lock(lock)     (((void)(lock), 1))
 236 #define write_can_lock(lock)    (((void)(lock), 1))
 237 #define _raw_read_trylock(lock) ({ (void)(lock); (1); })
 238 #define _raw_write_trylock(lock) ({ (void)(lock); (1); })
 239
 240 #define _spin_trylock(lock)     ({preempt_disable(); _raw_spin_trylock(lock) ? \
 241                                 1 : ({preempt_enable(); 0;});})
 242
 243 #define _read_trylock(lock)     ({preempt_disable();_raw_read_trylock(lock) ? \
 244                                 1 : ({preempt_enable(); 0;});})
 245
 246 #define _write_trylock(lock)    ({preempt_disable(); _raw_write_trylock(lock) ? \
 247                                 1 : ({preempt_enable(); 0;});})
 248
 249 #define _spin_trylock_bh(lock)  ({preempt_disable(); local_bh_disable(); \
 250                                 _raw_spin_trylock(lock) ? \
 251                                 1 : ({preempt_enable(); local_bh_enable(); 0;});})
 252
 253 #define _spin_lock(lock)        \
 254 do { \
 255         preempt_disable(); \
 256         _raw_spin_lock(lock); \
 257         __acquire(lock); \
 258 } while(0)
 259
 260 #define _write_lock(lock) \
 261 do { \
 262         preempt_disable(); \
 263         _raw_write_lock(lock); \
 264         __acquire(lock); \
 265 } while(0)
 266
 267 #define _read_lock(lock)        \
 268 do { \
 269         preempt_disable(); \
 270         _raw_read_lock(lock); \
 271         __acquire(lock); \
 272 } while(0)
 273
 274 #define _spin_unlock(lock) \
 275 do { \
 276         _raw_spin_unlock(lock); \
 277         preempt_enable(); \
 278         __release(lock); \
 279 } while (0)
 280
 281 #define _write_unlock(lock) \
 282 do { \
 283         _raw_write_unlock(lock); \
 284         preempt_enable(); \
 285         __release(lock); \
 286 } while(0)
 287
 288 #define _read_unlock(lock) \
 289 do { \
 290         _raw_read_unlock(lock); \
 291         preempt_enable(); \
 292         __release(lock); \
 293 } while(0)
 294
 295 #define _spin_lock_irqsave(lock, flags) \
 296 do {    \
 297         local_irq_save(flags); \
 298         preempt_disable(); \
 299         _raw_spin_lock(lock); \
 300         __acquire(lock); \
 301 } while (0)
 302
 303 #define _spin_lock_irq(lock) \
 304 do { \
 305         local_irq_disable(); \
 306         preempt_disable(); \
 307         _raw_spin_lock(lock); \
 308         __acquire(lock); \
 309 } while (0)
 310
 311 #define _spin_lock_bh(lock) \
 312 do { \
 313         local_bh_disable(); \
 314         preempt_disable(); \
 315         _raw_spin_lock(lock); \
 316         __acquire(lock); \
 317 } while (0)
 318
 319 #define _read_lock_irqsave(lock, flags) \
 320 do {    \
 321         local_irq_save(flags); \
 322         preempt_disable(); \
 323         _raw_read_lock(lock); \
 324         __acquire(lock); \
 325 } while (0)
 326
 327 #define _read_lock_irq(lock) \
 328 do { \
 329         local_irq_disable(); \
 330         preempt_disable(); \
 331         _raw_read_lock(lock); \
 332         __acquire(lock); \
 333 } while (0)
 334
 335 #define _read_lock_bh(lock) \
 336 do { \
 337         local_bh_disable(); \
 338         preempt_disable(); \
 339         _raw_read_lock(lock); \
 340         __acquire(lock); \
 341 } while (0)
 342
 343 #define _write_lock_irqsave(lock, flags) \
 344 do {    \
 345         local_irq_save(flags); \
 346         preempt_disable(); \
 347         _raw_write_lock(lock); \
 348         __acquire(lock); \
 349 } while (0)
 350
 351 #define _write_lock_irq(lock) \
 352 do { \
 353         local_irq_disable(); \
 354         preempt_disable(); \
 355         _raw_write_lock(lock); \
 356         __acquire(lock); \
 357 } while (0)
 358
 359 #define _write_lock_bh(lock) \
 360 do { \
 361         local_bh_disable(); \
 362         preempt_disable(); \
 363         _raw_write_lock(lock); \
 364         __acquire(lock); \
 365 } while (0)
 366
 367 #define _spin_unlock_irqrestore(lock, flags) \
 368 do { \
 369         _raw_spin_unlock(lock); \
 370         local_irq_restore(flags); \
 371         preempt_enable(); \
 372         __release(lock); \
 373 } while (0)
 374
 375 #define _spin_unlock_irq(lock) \
 376 do { \
 377         _raw_spin_unlock(lock); \
 378         local_irq_enable(); \
 379         preempt_enable(); \
 380         __release(lock); \
 381 } while (0)
 382
 383 #define _spin_unlock_bh(lock) \
 384 do { \
 385         _raw_spin_unlock(lock); \
 386         preempt_enable(); \
 387         local_bh_enable(); \
 388         __release(lock); \
 389 } while (0)
 390
 391 #define _write_unlock_bh(lock) \
 392 do { \
 393         _raw_write_unlock(lock); \
 394         preempt_enable(); \
 395         local_bh_enable(); \
 396         __release(lock); \
 397 } while (0)
 398
 399 #define _read_unlock_irqrestore(lock, flags) \
 400 do { \
 401         _raw_read_unlock(lock); \
 402         local_irq_restore(flags); \
 403         preempt_enable(); \
 404         __release(lock); \
 405 } while (0)
 406
 407 #define _write_unlock_irqrestore(lock, flags) \
 408 do { \
 409         _raw_write_unlock(lock); \
 410         local_irq_restore(flags); \
 411         preempt_enable(); \
 412         __release(lock); \
 413 } while (0)
 414
 415 #define _read_unlock_irq(lock)  \
 416 do { \
 417         _raw_read_unlock(lock); \
 418         local_irq_enable();     \
 419         preempt_enable();       \
 420         __release(lock); \
 421 } while (0)
 422
 423 #define _read_unlock_bh(lock)   \
 424 do { \
 425         _raw_read_unlock(lock); \
 426         local_bh_enable();      \
 427         preempt_enable();       \
 428         __release(lock); \
 429 } while (0)
 430
 431 #define _write_unlock_irq(lock) \
 432 do { \
 433         _raw_write_unlock(lock);        \
 434         local_irq_enable();     \
 435         preempt_enable();       \
 436         __release(lock); \
 437 } while (0)
 438
 439 #endif /* !SMP */
 440
 441 /*
 442  * Define the various spin_lock and rw_lock methods.  Note we define these
 443  * regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The various
 444  * methods are defined as nops in the case they are not required.
 445  */
 446 #define spin_trylock(lock)      __cond_lock(_spin_trylock(lock))
 447 #define read_trylock(lock)      __cond_lock(_read_trylock(lock))
 448 #define write_trylock(lock)     __cond_lock(_write_trylock(lock))
 449
 450 #define spin_lock(lock)         _spin_lock(lock)
 451 #define write_lock(lock)        _write_lock(lock)
 452 #define read_lock(lock)         _read_lock(lock)
 453
 454 #ifdef CONFIG_SMP
 455 #define spin_lock_irqsave(lock, flags)  flags = _spin_lock_irqsave(lock)
 456 #define read_lock_irqsave(lock, flags)  flags = _read_lock_irqsave(lock)
 457 #define write_lock_irqsave(lock, flags) flags = _write_lock_irqsave(lock)
 458 #else
 459 #define spin_lock_irqsave(lock, flags)  _spin_lock_irqsave(lock, flags)
 460 #define read_lock_irqsave(lock, flags)  _read_lock_irqsave(lock, flags)
 461 #define write_lock_irqsave(lock, flags) _write_lock_irqsave(lock, flags)
 462 #endif
 463
 464 #define spin_lock_irq(lock)             _spin_lock_irq(lock)
 465 #define spin_lock_bh(lock)              _spin_lock_bh(lock)
 466
 467 #define read_lock_irq(lock)             _read_lock_irq(lock)
 468 #define read_lock_bh(lock)              _read_lock_bh(lock)
 469
 470 #define write_lock_irq(lock)            _write_lock_irq(lock)
 471 #define write_lock_bh(lock)             _write_lock_bh(lock)
 472
 473 #define spin_unlock(lock)       _spin_unlock(lock)
 474 #define write_unlock(lock)      _write_unlock(lock)
 475 #define read_unlock(lock)       _read_unlock(lock)
 476
 477 #define spin_unlock_irqrestore(lock, flags)     _spin_unlock_irqrestore(lock, flags)
 478 #define spin_unlock_irq(lock)           _spin_unlock_irq(lock)
 479 #define spin_unlock_bh(lock)            _spin_unlock_bh(lock)
 480
 481 #define read_unlock_irqrestore(lock, flags)     _read_unlock_irqrestore(lock, flags)
 482 #define read_unlock_irq(lock)                   _read_unlock_irq(lock)
 483 #define read_unlock_bh(lock)                    _read_unlock_bh(lock)
 484
 485 #define write_unlock_irqrestore(lock, flags)    _write_unlock_irqrestore(lock, flags)
 486 #define write_unlock_irq(lock)                  _write_unlock_irq(lock)
 487 #define write_unlock_bh(lock)                   _write_unlock_bh(lock)
 488
 489 #define spin_trylock_bh(lock)                   __cond_lock(_spin_trylock_bh(lock))
 490
 491 #define spin_trylock_irq(lock) \
 492 ({ \
 493         local_irq_disable(); \
 494         _spin_trylock(lock) ? \
 495         1 : ({local_irq_enable(); 0; }); \
 496 })
 497
 498 #define spin_trylock_irqsave(lock, flags) \
 499 ({ \
 500         local_irq_save(flags); \
 501         _spin_trylock(lock) ? \
 502         1 : ({local_irq_restore(flags); 0;}); \
 503 })
 504
 505 #ifdef CONFIG_LOCKMETER
 506 extern void _metered_spin_lock   (spinlock_t *lock);
 507 extern void _metered_spin_unlock (spinlock_t *lock);
 508 extern int  _metered_spin_trylock(spinlock_t *lock);
 509 extern void _metered_read_lock    (rwlock_t *lock);
 510 extern void _metered_read_unlock  (rwlock_t *lock);
 511 extern void _metered_write_lock   (rwlock_t *lock);
 512 extern void _metered_write_unlock (rwlock_t *lock);
 513 extern int  _metered_read_trylock (rwlock_t *lock);
 514 extern int  _metered_write_trylock(rwlock_t *lock);
 515 #endif
 516
 517 /* "lock on reference count zero" */
 518 #ifndef ATOMIC_DEC_AND_LOCK
 519 #include <asm/atomic.h>
 520 extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock);
 521 #endif
 522
 523 #define atomic_dec_and_lock(atomic,lock) __cond_lock(_atomic_dec_and_lock(atomic,lock))
 524
 525 /*
 526  *  bit-based spin_lock()
 527  *
 528  * Don't use this unless you really need to: spin_lock() and spin_unlock()
 529  * are significantly faster.
 530  */
 531 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
 532 {
 533         /*
 534          * Assuming the lock is uncontended, this never enters
 535          * the body of the outer loop. If it is contended, then
 536          * within the inner loop a non-atomic test is used to
 537          * busywait with less bus contention for a good time to
 538          * attempt to acquire the lock bit.
 539          */
 540         preempt_disable();
 541 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 542         while (test_and_set_bit(bitnum, addr)) {
 543                 while (test_bit(bitnum, addr)) {
 544                         preempt_enable();
 545                         cpu_relax();
 546                         preempt_disable();
 547                 }
 548         }
 549 #endif
 550         __acquire(bitlock);
 551 }
 552
 553 /*
 554  * Return true if it was acquired
 555  */
 556 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
 557 {
 558         preempt_disable();
 559 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 560         if (test_and_set_bit(bitnum, addr)) {
 561                 preempt_enable();
 562                 return 0;
 563         }
 564 #endif
 565         __acquire(bitlock);
 566         return 1;
 567 }
 568
 569 /*
 570  *  bit-based spin_unlock()
 571  */
 572 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
 573 {
 574 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 575         BUG_ON(!test_bit(bitnum, addr));
 576         smp_mb__before_clear_bit();
 577         clear_bit(bitnum, addr);
 578 #endif
 579         preempt_enable();
 580         __release(bitlock);
 581 }
 582
 583 /*
 584  * Return true if the lock is held.
 585  */
 586 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
 587 {
 588 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
 589         return test_bit(bitnum, addr);
 590 #elif defined CONFIG_PREEMPT
 591         return preempt_count();
 592 #else
 593         return 1;
 594 #endif
 595 }
 596
 597 #define DEFINE_SPINLOCK(x) spinlock_t x = SPIN_LOCK_UNLOCKED
 598 #define DEFINE_RWLOCK(x) rwlock_t x = RW_LOCK_UNLOCKED
 599
 600 /**
 601  * spin_can_lock - would spin_trylock() succeed?
 602  * @lock: the spinlock in question.
 603  */
 604 #define spin_can_lock(lock)             (!spin_is_locked(lock))
 605
 606 #endif /* __LINUX_SPINLOCK_H */