code.delx.au - pulseaudio/blob - src/pulsecore/memtrap.c

   1 /***
   2   This file is part of PulseAudio.
   3
   4   Copyright 2009 Lennart Poettering
   5
   6   PulseAudio is free software; you can redistribute it and/or modify
   7   it under the terms of the GNU Lesser General Public License as
   8   published by the Free Software Foundation; either version 2.1 of the
   9   License, or (at your option) any later version.
  10
  11   PulseAudio is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public
  17   License along with PulseAudio; if not, write to the Free Software
  18   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  19   USA.
  20 ***/
  21
  22 #ifdef HAVE_CONFIG_H
  23 #include <config.h>
  24 #endif
  25
  26 #include <signal.h>
  27 #include <sys/mman.h>
  28
  29 #include <pulse/xmalloc.h>
  30
  31 #include <pulsecore/semaphore.h>
  32 #include <pulsecore/macro.h>
  33 #include <pulsecore/mutex.h>
  34 #include <pulsecore/core-util.h>
  35
  36 #include "memtrap.h"
  37
  38 struct pa_memtrap {
  39     void *start;
  40     size_t size;
  41     pa_atomic_t bad;
  42     pa_memtrap *next[2], *prev[2];
  43 };
  44
  45 static pa_memtrap *memtraps[2] = { NULL, NULL };
  46 static pa_atomic_t read_lock = PA_ATOMIC_INIT(0);
  47 static pa_static_semaphore semaphore = PA_STATIC_SEMAPHORE_INIT;
  48 static pa_static_mutex write_lock = PA_STATIC_MUTEX_INIT;
  49
  50 #define MSB (1U << (sizeof(unsigned)*8U-1))
  51 #define WHICH(n) (!!((n) & MSB))
  52 #define COUNTER(n) ((n) & ~MSB)
  53
  54 pa_bool_t pa_memtrap_is_good(pa_memtrap *m) {
  55     pa_assert(m);
  56
  57     return !pa_atomic_load(&m->bad);
  58 }
  59
  60 static void sigsafe_error(const char *s) {
  61     write(STDERR_FILENO, s, strlen(s));
  62 }
  63
  64 static void signal_handler(int sig, siginfo_t* si, void *data) {
  65     unsigned n, j;
  66     pa_memtrap *m;
  67     void *r;
  68
  69     /* Increase the lock counter */
  70     n = (unsigned) pa_atomic_inc(&read_lock);
  71
  72     /* The uppermost bit tells us which list to look at */
  73     j = WHICH(n);
  74
  75     /* When n is 0 we have about 2^31 threads running that
  76      * all got a sigbus at the same time, oh my! */
  77     pa_assert(COUNTER(n)+1 > 0);
  78
  79     for (m = memtraps[j]; m; m = m->next[j])
  80         if (si->si_addr >= m->start &&
  81             (uint8_t*) si->si_addr < (uint8_t*) m->start + m->size)
  82             break;
  83
  84     if (!m)
  85         goto fail;
  86
  87     pa_atomic_store(&m->bad, 1);
  88
  89     /* Remap anonymous memory into the bad segment */
  90     if ((r = mmap(m->start, m->size, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_FIXED|MAP_PRIVATE, -1, 0)) == MAP_FAILED) {
  91         sigsafe_error("mmap() failed.\n");
  92         goto fail;
  93     }
  94
  95     pa_assert(r == m->start);
  96
  97     pa_atomic_dec(&read_lock);
  98
  99     /* Post the semaphore */
 100     pa_semaphore_post(pa_static_semaphore_get(&semaphore, 0));
 101
 102     return;
 103
 104 fail:
 105     pa_atomic_dec(&read_lock);
 106     abort();
 107 }
 108
 109 static void memtrap_swap(unsigned n) {
 110
 111     for (;;) {
 112
 113         /* If the read counter is > 0 wait; if it is 0 try to swap the lists */
 114         if (COUNTER(n) > 0)
 115             pa_semaphore_wait(pa_static_semaphore_get(&semaphore, 0));
 116         else if (pa_atomic_cmpxchg(&read_lock, (int) n, (int) (n ^ MSB)))
 117             break;
 118
 119         n = (unsigned) pa_atomic_load(&read_lock);
 120     }
 121 }
 122
 123 static void memtrap_link(pa_memtrap *m, unsigned j) {
 124     pa_assert(m);
 125
 126     m->prev[j] = NULL;
 127     m->next[j] = memtraps[j];
 128     memtraps[j] = m;
 129 }
 130
 131 static void memtrap_unlink(pa_memtrap *m, int j) {
 132     pa_assert(m);
 133
 134     if (m->next[j])
 135         m->next[j]->prev[j] = m->prev[j];
 136
 137     if (m->prev[j])
 138         m->prev[j]->next[j] = m->next[j];
 139     else
 140         memtraps[j] = m->next[j];
 141 }
 142
 143 pa_memtrap* pa_memtrap_add(const void *start, size_t size) {
 144     pa_memtrap *m = NULL;
 145     pa_mutex *lock;
 146     unsigned n, j;
 147
 148     pa_assert(start);
 149     pa_assert(size > 0);
 150     pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
 151     pa_assert(PA_PAGE_ALIGN(size) == size);
 152
 153     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 154     pa_mutex_lock(lock);
 155
 156     if (!memtraps[0]) {
 157         struct sigaction sa;
 158
 159         /* Before we install the signal handler, make sure the
 160          * semaphore is valid so that the initialization of the
 161          * semaphore doesn't have to happen from the signal handler */
 162         pa_static_semaphore_get(&semaphore, 0);
 163
 164         memset(&sa, 0, sizeof(sa));
 165         sa.sa_sigaction = signal_handler;
 166         sa.sa_flags = SA_RESTART|SA_SIGINFO;
 167
 168         pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
 169     }
 170
 171     n = (unsigned) pa_atomic_load(&read_lock);
 172     j = WHICH(n);
 173
 174     m = pa_xnew(pa_memtrap, 1);
 175     m->start = (void*) start;
 176     m->size = size;
 177     pa_atomic_store(&m->bad, 0);
 178
 179     memtrap_link(m, !j);
 180     memtrap_swap(n);
 181     memtrap_link(m, j);
 182
 183     pa_mutex_unlock(lock);
 184
 185     return m;
 186 }
 187
 188 void pa_memtrap_remove(pa_memtrap *m) {
 189     unsigned n, j;
 190     pa_mutex *lock;
 191
 192     pa_assert(m);
 193
 194     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 195     pa_mutex_lock(lock);
 196
 197     n = (unsigned) pa_atomic_load(&read_lock);
 198     j = WHICH(n);
 199
 200     memtrap_unlink(m, !j);
 201     memtrap_swap(n);
 202     memtrap_unlink(m, j);
 203
 204     pa_xfree(m);
 205
 206     if (!memtraps[0]) {
 207         struct sigaction sa;
 208
 209         memset(&sa, 0, sizeof(sa));
 210         sa.sa_handler = SIG_DFL;
 211         pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
 212     }
 213
 214     pa_mutex_unlock(lock);
 215 }
 216
 217 pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size) {
 218     unsigned n, j;
 219     pa_mutex *lock;
 220
 221     pa_assert(m);
 222
 223     pa_assert(start);
 224     pa_assert(size > 0);
 225     pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
 226     pa_assert(PA_PAGE_ALIGN(size) == size);
 227
 228     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 229     pa_mutex_lock(lock);
 230
 231     if (m->start == start && m->size == size)
 232         goto unlock;
 233
 234     n = (unsigned) pa_atomic_load(&read_lock);
 235     j = WHICH(n);
 236
 237     memtrap_unlink(m, !j);
 238     memtrap_swap(n);
 239     memtrap_unlink(m, j);
 240
 241     m->start = (void*) start;
 242     m->size = size;
 243     pa_atomic_store(&m->bad, 0);
 244
 245     n = (unsigned) pa_atomic_load(&read_lock);
 246     j = WHICH(n);
 247
 248     memtrap_link(m, !j);
 249     memtrap_swap(n);
 250     memtrap_link(m, j);
 251
 252 unlock:
 253     pa_mutex_unlock(lock);
 254
 255     return m;
 256 }