nptl/pthread_mutex_init.c

   1 /* Copyright (C) 2002-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <stdbool.h>
  21 #include <string.h>
  22 #include <kernel-features.h>
  23 #include "pthreadP.h"
  24 #include <atomic.h>
  25 #include <pthread-offsets.h>
  26 #include <futex-internal.h>
  27 #include <shlib-compat.h>
  28
  29 #include <stap-probe.h>
  30
  31 static const struct pthread_mutexattr default_mutexattr =
  32   {
  33     /* Default is a normal mutex, not shared between processes.  */
  34     .mutexkind = PTHREAD_MUTEX_NORMAL
  35   };
  36
  37
  38 static bool
  39 prio_inherit_missing (void)
  40 {
  41   static int tpi_supported;
  42   if (__glibc_unlikely (atomic_load_relaxed (&tpi_supported) == 0))
  43     {
  44       int e = futex_unlock_pi (&(unsigned int){0}, 0);
  45       atomic_store_relaxed (&tpi_supported, e == ENOSYS ? -1 : 1);
  46     }
  47   return __glibc_unlikely (tpi_supported < 0);
  48 }
  49
  50 int
  51 ___pthread_mutex_init (pthread_mutex_t *mutex,
  52                       const pthread_mutexattr_t *mutexattr)
  53 {
  54   const struct pthread_mutexattr *imutexattr;
  55
  56   ASSERT_TYPE_SIZE (pthread_mutex_t, __SIZEOF_PTHREAD_MUTEX_T);
  57
  58   /* __kind is the only field where its offset should be checked to
  59      avoid ABI breakage with static initializers.  */
  60   ASSERT_PTHREAD_INTERNAL_OFFSET (pthread_mutex_t, __data.__kind,
  61                                   __PTHREAD_MUTEX_KIND_OFFSET);
  62   ASSERT_PTHREAD_INTERNAL_MEMBER_SIZE (pthread_mutex_t, __data.__kind, int);
  63
  64   imutexattr = ((const struct pthread_mutexattr *) mutexattr
  65                 ?: &default_mutexattr);
  66
  67   /* Sanity checks.  */
  68   switch (__builtin_expect (imutexattr->mutexkind
  69                             & PTHREAD_MUTEXATTR_PROTOCOL_MASK,
  70                             PTHREAD_PRIO_NONE
  71                             << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT))
  72     {
  73     case PTHREAD_PRIO_NONE << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
  74       break;
  75
  76     case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
  77       if (__glibc_unlikely (prio_inherit_missing ()))
  78         return ENOTSUP;
  79       break;
  80
  81     default:
  82       /* XXX: For now we don't support robust priority protected mutexes.  */
  83       if (imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_ROBUST)
  84         return ENOTSUP;
  85       break;
  86     }
  87
  88   /* Clear the whole variable.  */
  89   memset (mutex, '\0', __SIZEOF_PTHREAD_MUTEX_T);
  90
  91   /* Copy the values from the attribute.  */
  92   int mutex_kind = imutexattr->mutexkind & ~PTHREAD_MUTEXATTR_FLAG_BITS;
  93
  94   if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_ROBUST) != 0)
  95     {
  96 #ifndef __ASSUME_SET_ROBUST_LIST
  97       if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_PSHARED) != 0
  98           && !__nptl_set_robust_list_avail)
  99         return ENOTSUP;
 100 #endif
 101
 102       mutex_kind |= PTHREAD_MUTEX_ROBUST_NORMAL_NP;
 103     }
 104
 105   switch (imutexattr->mutexkind & PTHREAD_MUTEXATTR_PROTOCOL_MASK)
 106     {
 107     case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
 108       mutex_kind |= PTHREAD_MUTEX_PRIO_INHERIT_NP;
 109       break;
 110
 111     case PTHREAD_PRIO_PROTECT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
 112       mutex_kind |= PTHREAD_MUTEX_PRIO_PROTECT_NP;
 113
 114       int ceiling = (imutexattr->mutexkind
 115                      & PTHREAD_MUTEXATTR_PRIO_CEILING_MASK)
 116                     >> PTHREAD_MUTEXATTR_PRIO_CEILING_SHIFT;
 117       if (! ceiling)
 118         {
 119           /* See __init_sched_fifo_prio.  */
 120           if (atomic_load_relaxed (&__sched_fifo_min_prio) == -1)
 121             __init_sched_fifo_prio ();
 122           if (ceiling < atomic_load_relaxed (&__sched_fifo_min_prio))
 123             ceiling = atomic_load_relaxed (&__sched_fifo_min_prio);
 124         }
 125       mutex->__data.__lock = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
 126       break;
 127
 128     default:
 129       break;
 130     }
 131
 132   /* The kernel when waking robust mutexes on exit never uses
 133      FUTEX_PRIVATE_FLAG FUTEX_WAKE.  */
 134   if ((imutexattr->mutexkind & (PTHREAD_MUTEXATTR_FLAG_PSHARED
 135                                 | PTHREAD_MUTEXATTR_FLAG_ROBUST)) != 0)
 136     mutex_kind |= PTHREAD_MUTEX_PSHARED_BIT;
 137
 138   /* See concurrency notes regarding __kind in struct __pthread_mutex_s
 139      in sysdeps/nptl/bits/thread-shared-types.h.  */
 140   atomic_store_relaxed (&(mutex->__data.__kind), mutex_kind);
 141
 142   /* Default values: mutex not used yet.  */
 143   // mutex->__count = 0;        already done by memset
 144   // mutex->__owner = 0;        already done by memset
 145   // mutex->__nusers = 0;       already done by memset
 146   // mutex->__spins = 0;        already done by memset
 147   // mutex->__next = NULL;      already done by memset
 148
 149   LIBC_PROBE (mutex_init, 1, mutex);
 150
 151   return 0;
 152 }
 153 versioned_symbol (libpthread, ___pthread_mutex_init, pthread_mutex_init,
 154                   GLIBC_2_0);
 155 libc_hidden_ver (___pthread_mutex_init, __pthread_mutex_init)
 156 #ifndef SHARED
 157 strong_alias (___pthread_mutex_init, __pthread_mutex_init)
 158 #endif
 159
 160 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_34)
 161 compat_symbol (libpthread, ___pthread_mutex_init, __pthread_mutex_init,
 162                GLIBC_2_0);
 163 #endif