nptl/pthread_mutex_setprioceiling.c

   1 /* Set current priority ceiling of pthread_mutex_t.
   2    Copyright (C) 2006-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jakub Jelinek <jakub@redhat.com>, 2006.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <stdbool.h>
  21 #include <errno.h>
  22 #include <pthreadP.h>
  23 #include <atomic.h>
  24
  25
  26 int
  27 pthread_mutex_setprioceiling (pthread_mutex_t *mutex, int prioceiling,
  28                               int *old_ceiling)
  29 {
  30   /* The low bits of __kind aren't ever changed after pthread_mutex_init,
  31      so we don't need a lock yet.  */
  32   if ((mutex->__data.__kind & PTHREAD_MUTEX_PRIO_PROTECT_NP) == 0)
  33     return EINVAL;
  34
  35   /* See __init_sched_fifo_prio.  */
  36   if (atomic_load_relaxed (&__sched_fifo_min_prio) == -1
  37       || atomic_load_relaxed (&__sched_fifo_max_prio) == -1)
  38     __init_sched_fifo_prio ();
  39
  40   if (__glibc_unlikely (prioceiling
  41                         < atomic_load_relaxed (&__sched_fifo_min_prio))
  42       || __glibc_unlikely (prioceiling
  43                            > atomic_load_relaxed (&__sched_fifo_max_prio))
  44       || __glibc_unlikely ((prioceiling
  45                             & (PTHREAD_MUTEXATTR_PRIO_CEILING_MASK
  46                                >> PTHREAD_MUTEXATTR_PRIO_CEILING_SHIFT))
  47                            != prioceiling))
  48     return EINVAL;
  49
  50   /* Check whether we already hold the mutex.  */
  51   bool locked = false;
  52   int kind = PTHREAD_MUTEX_TYPE (mutex);
  53   if (mutex->__data.__owner == THREAD_GETMEM (THREAD_SELF, tid))
  54     {
  55       if (kind == PTHREAD_MUTEX_PP_ERRORCHECK_NP)
  56         return EDEADLK;
  57
  58       if (kind == PTHREAD_MUTEX_PP_RECURSIVE_NP)
  59         locked = true;
  60     }
  61
  62   int oldval = mutex->__data.__lock;
  63   if (! locked)
  64     do
  65       {
  66         /* Need to lock the mutex, but without obeying the priority
  67            protect protocol.  */
  68         int ceilval = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK);
  69
  70         oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  71                                                       ceilval | 1, ceilval);
  72         if (oldval == ceilval)
  73           break;
  74
  75         do
  76           {
  77             oldval
  78               = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  79                                                      ceilval | 2,
  80                                                      ceilval | 1);
  81
  82             if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
  83               break;
  84
  85             if (oldval != ceilval)
  86               lll_futex_wait (&mutex->__data.__lock, ceilval | 2,
  87                               PTHREAD_MUTEX_PSHARED (mutex));
  88           }
  89         while (atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  90                                                     ceilval | 2, ceilval)
  91                != ceilval);
  92
  93         if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
  94           continue;
  95       }
  96     while (0);
  97
  98   int oldprio = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
  99                 >> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 100   if (locked)
 101     {
 102       int ret = __pthread_tpp_change_priority (oldprio, prioceiling);
 103       if (ret)
 104         return ret;
 105     }
 106
 107   if (old_ceiling != NULL)
 108     *old_ceiling = oldprio;
 109
 110   int newlock = 0;
 111   if (locked)
 112     newlock = (mutex->__data.__lock & ~PTHREAD_MUTEX_PRIO_CEILING_MASK);
 113   mutex->__data.__lock = newlock
 114                          | (prioceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT);
 115   atomic_full_barrier ();
 116
 117   lll_futex_wake (&mutex->__data.__lock, INT_MAX,
 118                   PTHREAD_MUTEX_PSHARED (mutex));
 119
 120   return 0;
 121 }