nptl/pthread_mutex_init.c

   1 /* Copyright (C) 2002-2021 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <stdbool.h>
  22 #include <string.h>
  23 #include <kernel-features.h>
  24 #include "pthreadP.h"
  25 #include <atomic.h>
  26 #include <pthread-offsets.h>
  27 #include <futex-internal.h>
  28 #include <shlib-compat.h>
  29
  30 #include <stap-probe.h>
  31
  32 static const struct pthread_mutexattr default_mutexattr =
  33   {
  34     /* Default is a normal mutex, not shared between processes.  */
  35     .mutexkind = PTHREAD_MUTEX_NORMAL
  36   };
  37
  38
  39 static bool
  40 prio_inherit_missing (void)
  41 {
  42   static int tpi_supported;
  43   if (__glibc_unlikely (atomic_load_relaxed (&tpi_supported) == 0))
  44     {
  45       int e = futex_unlock_pi (&(unsigned int){0}, 0);
  46       atomic_store_relaxed (&tpi_supported, e == ENOSYS ? -1 : 1);
  47     }
  48   return __glibc_unlikely (tpi_supported < 0);
  49 }
  50
  51 int
  52 ___pthread_mutex_init (pthread_mutex_t *mutex,
  53                       const pthread_mutexattr_t *mutexattr)
  54 {
  55   const struct pthread_mutexattr *imutexattr;
  56
  57   ASSERT_TYPE_SIZE (pthread_mutex_t, __SIZEOF_PTHREAD_MUTEX_T);
  58
  59   /* __kind is the only field where its offset should be checked to
  60      avoid ABI breakage with static initializers.  */
  61   ASSERT_PTHREAD_INTERNAL_OFFSET (pthread_mutex_t, __data.__kind,
  62                                   __PTHREAD_MUTEX_KIND_OFFSET);
  63   ASSERT_PTHREAD_INTERNAL_MEMBER_SIZE (pthread_mutex_t, __data.__kind, int);
  64
  65   imutexattr = ((const struct pthread_mutexattr *) mutexattr
  66                 ?: &default_mutexattr);
  67
  68   /* Sanity checks.  */
  69   switch (__builtin_expect (imutexattr->mutexkind
  70                             & PTHREAD_MUTEXATTR_PROTOCOL_MASK,
  71                             PTHREAD_PRIO_NONE
  72                             << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT))
  73     {
  74     case PTHREAD_PRIO_NONE << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
  75       break;
  76
  77     case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
  78       if (__glibc_unlikely (prio_inherit_missing ()))
  79         return ENOTSUP;
  80       break;
  81
  82     default:
  83       /* XXX: For now we don't support robust priority protected mutexes.  */
  84       if (imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_ROBUST)
  85         return ENOTSUP;
  86       break;
  87     }
  88
  89   /* Clear the whole variable.  */
  90   memset (mutex, '\0', __SIZEOF_PTHREAD_MUTEX_T);
  91
  92   /* Copy the values from the attribute.  */
  93   int mutex_kind = imutexattr->mutexkind & ~PTHREAD_MUTEXATTR_FLAG_BITS;
  94
  95   if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_ROBUST) != 0)
  96     {
  97 #ifndef __ASSUME_SET_ROBUST_LIST
  98       if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_PSHARED) != 0
  99           && !__nptl_set_robust_list_avail)
 100         return ENOTSUP;
 101 #endif
 102
 103       mutex_kind |= PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 104     }
 105
 106   switch (imutexattr->mutexkind & PTHREAD_MUTEXATTR_PROTOCOL_MASK)
 107     {
 108     case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
 109       mutex_kind |= PTHREAD_MUTEX_PRIO_INHERIT_NP;
 110       break;
 111
 112     case PTHREAD_PRIO_PROTECT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
 113       mutex_kind |= PTHREAD_MUTEX_PRIO_PROTECT_NP;
 114
 115       int ceiling = (imutexattr->mutexkind
 116                      & PTHREAD_MUTEXATTR_PRIO_CEILING_MASK)
 117                     >> PTHREAD_MUTEXATTR_PRIO_CEILING_SHIFT;
 118       if (! ceiling)
 119         {
 120           /* See __init_sched_fifo_prio.  */
 121           if (atomic_load_relaxed (&__sched_fifo_min_prio) == -1)
 122             __init_sched_fifo_prio ();
 123           if (ceiling < atomic_load_relaxed (&__sched_fifo_min_prio))
 124             ceiling = atomic_load_relaxed (&__sched_fifo_min_prio);
 125         }
 126       mutex->__data.__lock = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 127       break;
 128
 129     default:
 130       break;
 131     }
 132
 133   /* The kernel when waking robust mutexes on exit never uses
 134      FUTEX_PRIVATE_FLAG FUTEX_WAKE.  */
 135   if ((imutexattr->mutexkind & (PTHREAD_MUTEXATTR_FLAG_PSHARED
 136                                 | PTHREAD_MUTEXATTR_FLAG_ROBUST)) != 0)
 137     mutex_kind |= PTHREAD_MUTEX_PSHARED_BIT;
 138
 139   /* See concurrency notes regarding __kind in struct __pthread_mutex_s
 140      in sysdeps/nptl/bits/thread-shared-types.h.  */
 141   atomic_store_relaxed (&(mutex->__data.__kind), mutex_kind);
 142
 143   /* Default values: mutex not used yet.  */
 144   // mutex->__count = 0;        already done by memset
 145   // mutex->__owner = 0;        already done by memset
 146   // mutex->__nusers = 0;       already done by memset
 147   // mutex->__spins = 0;        already done by memset
 148   // mutex->__next = NULL;      already done by memset
 149
 150   LIBC_PROBE (mutex_init, 1, mutex);
 151
 152   return 0;
 153 }
 154 versioned_symbol (libpthread, ___pthread_mutex_init, pthread_mutex_init,
 155                   GLIBC_2_0);
 156 libc_hidden_ver (___pthread_mutex_init, __pthread_mutex_init)
 157 #ifndef SHARED
 158 strong_alias (___pthread_mutex_init, __pthread_mutex_init)
 159 #endif
 160
 161 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_34)
 162 compat_symbol (libpthread, ___pthread_mutex_init, __pthread_mutex_init,
 163                GLIBC_2_0);
 164 #endif