nptl/pthread_mutex_trylock.c

   1 /* Copyright (C) 2002-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <stdlib.h>
  22 #include "pthreadP.h"
  23 #include <lowlevellock.h>
  24
  25 #ifndef lll_trylock_elision
  26 #define lll_trylock_elision(a,t) lll_trylock(a)
  27 #endif
  28
  29 #ifndef FORCE_ELISION
  30 #define FORCE_ELISION(m, s)
  31 #endif
  32
  33 int
  34 __pthread_mutex_trylock (pthread_mutex_t *mutex)
  35 {
  36   int oldval;
  37   pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
  38
  39   switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),
  40                             PTHREAD_MUTEX_TIMED_NP))
  41     {
  42       /* Recursive mutex.  */
  43     case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:
  44     case PTHREAD_MUTEX_RECURSIVE_NP:
  45       /* Check whether we already hold the mutex.  */
  46       if (mutex->__data.__owner == id)
  47         {
  48           /* Just bump the counter.  */
  49           if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
  50             /* Overflow of the counter.  */
  51             return EAGAIN;
  52
  53           ++mutex->__data.__count;
  54           return 0;
  55         }
  56
  57       if (lll_trylock (mutex->__data.__lock) == 0)
  58         {
  59           /* Record the ownership.  */
  60           mutex->__data.__owner = id;
  61           mutex->__data.__count = 1;
  62           ++mutex->__data.__nusers;
  63           return 0;
  64         }
  65       break;
  66
  67     case PTHREAD_MUTEX_TIMED_ELISION_NP:
  68     elision: __attribute__((unused))
  69       if (lll_trylock_elision (mutex->__data.__lock,
  70                                mutex->__data.__elision) != 0)
  71         break;
  72       /* Don't record the ownership.  */
  73       return 0;
  74
  75     case PTHREAD_MUTEX_TIMED_NP:
  76       FORCE_ELISION (mutex, goto elision);
  77       /*FALL THROUGH*/
  78     case PTHREAD_MUTEX_ADAPTIVE_NP:
  79     case PTHREAD_MUTEX_ERRORCHECK_NP:
  80       if (lll_trylock (mutex->__data.__lock) != 0)
  81         break;
  82
  83       /* Record the ownership.  */
  84       mutex->__data.__owner = id;
  85       ++mutex->__data.__nusers;
  86
  87       return 0;
  88
  89     case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
  90     case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
  91     case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
  92     case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
  93       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
  94                      &mutex->__data.__list.__next);
  95
  96       oldval = mutex->__data.__lock;
  97       do
  98         {
  99         again:
 100           if ((oldval & FUTEX_OWNER_DIED) != 0)
 101             {
 102               /* The previous owner died.  Try locking the mutex.  */
 103               int newval = id | (oldval & FUTEX_WAITERS);
 104
 105               newval
 106                 = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 107                                                        newval, oldval);
 108
 109               if (newval != oldval)
 110                 {
 111                   oldval = newval;
 112                   goto again;
 113                 }
 114
 115               /* We got the mutex.  */
 116               mutex->__data.__count = 1;
 117               /* But it is inconsistent unless marked otherwise.  */
 118               mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 119
 120               ENQUEUE_MUTEX (mutex);
 121               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 122
 123               /* Note that we deliberately exist here.  If we fall
 124                  through to the end of the function __nusers would be
 125                  incremented which is not correct because the old
 126                  owner has to be discounted.  */
 127               return EOWNERDEAD;
 128             }
 129
 130           /* Check whether we already hold the mutex.  */
 131           if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 132             {
 133               int kind = PTHREAD_MUTEX_TYPE (mutex);
 134               if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
 135                 {
 136                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 137                                  NULL);
 138                   return EDEADLK;
 139                 }
 140
 141               if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
 142                 {
 143                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 144                                  NULL);
 145
 146                   /* Just bump the counter.  */
 147                   if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 148                     /* Overflow of the counter.  */
 149                     return EAGAIN;
 150
 151                   ++mutex->__data.__count;
 152
 153                   return 0;
 154                 }
 155             }
 156
 157           oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 158                                                         id, 0);
 159           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 160             {
 161               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 162
 163               return EBUSY;
 164             }
 165
 166           if (__builtin_expect (mutex->__data.__owner
 167                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 168             {
 169               /* This mutex is now not recoverable.  */
 170               mutex->__data.__count = 0;
 171               if (oldval == id)
 172                 lll_unlock (mutex->__data.__lock,
 173                             PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 174               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 175               return ENOTRECOVERABLE;
 176             }
 177         }
 178       while ((oldval & FUTEX_OWNER_DIED) != 0);
 179
 180       ENQUEUE_MUTEX (mutex);
 181       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 182
 183       mutex->__data.__owner = id;
 184       ++mutex->__data.__nusers;
 185       mutex->__data.__count = 1;
 186
 187       return 0;
 188
 189     /* The PI support requires the Linux futex system call.  If that's not
 190        available, pthread_mutex_init should never have allowed the type to
 191        be set.  So it will get the default case for an invalid type.  */
 192 #ifdef __NR_futex
 193     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
 194     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
 195     case PTHREAD_MUTEX_PI_NORMAL_NP:
 196     case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
 197     case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
 198     case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
 199     case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
 200     case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
 201       {
 202         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 203         int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 204
 205         if (robust)
 206           /* Note: robust PI futexes are signaled by setting bit 0.  */
 207           THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 208                          (void *) (((uintptr_t) &mutex->__data.__list.__next)
 209                                    | 1));
 210
 211         oldval = mutex->__data.__lock;
 212
 213         /* Check whether we already hold the mutex.  */
 214         if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
 215           {
 216             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 217               {
 218                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 219                 return EDEADLK;
 220               }
 221
 222             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 223               {
 224                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 225
 226                 /* Just bump the counter.  */
 227                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 228                   /* Overflow of the counter.  */
 229                   return EAGAIN;
 230
 231                 ++mutex->__data.__count;
 232
 233                 return 0;
 234               }
 235           }
 236
 237         oldval
 238           = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 239                                                  id, 0);
 240
 241         if (oldval != 0)
 242           {
 243             if ((oldval & FUTEX_OWNER_DIED) == 0)
 244               {
 245                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 246
 247                 return EBUSY;
 248               }
 249
 250             assert (robust);
 251
 252             /* The mutex owner died.  The kernel will now take care of
 253                everything.  */
 254             int private = (robust
 255                            ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
 256                            : PTHREAD_MUTEX_PSHARED (mutex));
 257             INTERNAL_SYSCALL_DECL (__err);
 258             int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 259                                       __lll_private_flag (FUTEX_TRYLOCK_PI,
 260                                                           private), 0, 0);
 261
 262             if (INTERNAL_SYSCALL_ERROR_P (e, __err)
 263                 && INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
 264               {
 265                 THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 266
 267                 return EBUSY;
 268               }
 269
 270             oldval = mutex->__data.__lock;
 271           }
 272
 273         if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
 274           {
 275             atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
 276
 277             /* We got the mutex.  */
 278             mutex->__data.__count = 1;
 279             /* But it is inconsistent unless marked otherwise.  */
 280             mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 281
 282             ENQUEUE_MUTEX (mutex);
 283             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 284
 285             /* Note that we deliberately exit here.  If we fall
 286                through to the end of the function __nusers would be
 287                incremented which is not correct because the old owner
 288                has to be discounted.  */
 289             return EOWNERDEAD;
 290           }
 291
 292         if (robust
 293             && __builtin_expect (mutex->__data.__owner
 294                                  == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 295           {
 296             /* This mutex is now not recoverable.  */
 297             mutex->__data.__count = 0;
 298
 299             INTERNAL_SYSCALL_DECL (__err);
 300             INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
 301                               __lll_private_flag (FUTEX_UNLOCK_PI,
 302                                                   PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
 303                               0, 0);
 304
 305             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 306             return ENOTRECOVERABLE;
 307           }
 308
 309         if (robust)
 310           {
 311             ENQUEUE_MUTEX_PI (mutex);
 312             THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 313           }
 314
 315         mutex->__data.__owner = id;
 316         ++mutex->__data.__nusers;
 317         mutex->__data.__count = 1;
 318
 319         return 0;
 320       }
 321 #endif  /* __NR_futex.  */
 322
 323     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
 324     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
 325     case PTHREAD_MUTEX_PP_NORMAL_NP:
 326     case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
 327       {
 328         int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
 329
 330         oldval = mutex->__data.__lock;
 331
 332         /* Check whether we already hold the mutex.  */
 333         if (mutex->__data.__owner == id)
 334           {
 335             if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
 336               return EDEADLK;
 337
 338             if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
 339               {
 340                 /* Just bump the counter.  */
 341                 if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
 342                   /* Overflow of the counter.  */
 343                   return EAGAIN;
 344
 345                 ++mutex->__data.__count;
 346
 347                 return 0;
 348               }
 349           }
 350
 351         int oldprio = -1, ceilval;
 352         do
 353           {
 354             int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
 355                           >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 356
 357             if (__pthread_current_priority () > ceiling)
 358               {
 359                 if (oldprio != -1)
 360                   __pthread_tpp_change_priority (oldprio, -1);
 361                 return EINVAL;
 362               }
 363
 364             int retval = __pthread_tpp_change_priority (oldprio, ceiling);
 365             if (retval)
 366               return retval;
 367
 368             ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 369             oldprio = ceiling;
 370
 371             oldval
 372               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 373                                                      ceilval | 1, ceilval);
 374
 375             if (oldval == ceilval)
 376               break;
 377           }
 378         while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
 379
 380         if (oldval != ceilval)
 381           {
 382             __pthread_tpp_change_priority (oldprio, -1);
 383             break;
 384           }
 385
 386         assert (mutex->__data.__owner == 0);
 387         /* Record the ownership.  */
 388         mutex->__data.__owner = id;
 389         ++mutex->__data.__nusers;
 390         mutex->__data.__count = 1;
 391
 392         return 0;
 393       }
 394       break;
 395
 396     default:
 397       /* Correct code cannot set any other type.  */
 398       return EINVAL;
 399     }
 400
 401   return EBUSY;
 402 }
 403
 404 #ifndef __pthread_mutex_trylock
 405 #ifndef pthread_mutex_trylock
 406 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
 407 #endif
 408 #endif