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     sigsafe_error("Failed to handle SIGBUS.\n");
 106     pa_atomic_dec(&read_lock);
 107     abort();
 108 }
 109
 110 static void memtrap_swap(unsigned n) {
 111
 112     for (;;) {
 113
 114         /* If the read counter is > 0 wait; if it is 0 try to swap the lists */
 115         if (COUNTER(n) > 0)
 116             pa_semaphore_wait(pa_static_semaphore_get(&semaphore, 0));
 117         else if (pa_atomic_cmpxchg(&read_lock, (int) n, (int) (n ^ MSB)))
 118             break;
 119
 120         n = (unsigned) pa_atomic_load(&read_lock);
 121     }
 122 }
 123
 124 static void memtrap_link(pa_memtrap *m, unsigned j) {
 125     pa_assert(m);
 126
 127     m->prev[j] = NULL;
 128     m->next[j] = memtraps[j];
 129     memtraps[j] = m;
 130 }
 131
 132 static void memtrap_unlink(pa_memtrap *m, int j) {
 133     pa_assert(m);
 134
 135     if (m->next[j])
 136         m->next[j]->prev[j] = m->prev[j];
 137
 138     if (m->prev[j])
 139         m->prev[j]->next[j] = m->next[j];
 140     else
 141         memtraps[j] = m->next[j];
 142 }
 143
 144 pa_memtrap* pa_memtrap_add(const void *start, size_t size) {
 145     pa_memtrap *m = NULL;
 146     pa_mutex *lock;
 147     unsigned n, j;
 148
 149     pa_assert(start);
 150     pa_assert(size > 0);
 151     pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
 152     pa_assert(PA_PAGE_ALIGN(size) == size);
 153
 154     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 155     pa_mutex_lock(lock);
 156
 157     if (!memtraps[0]) {
 158         struct sigaction sa;
 159
 160         /* Before we install the signal handler, make sure the
 161          * semaphore is valid so that the initialization of the
 162          * semaphore doesn't have to happen from the signal handler */
 163         pa_static_semaphore_get(&semaphore, 0);
 164
 165         memset(&sa, 0, sizeof(sa));
 166         sa.sa_sigaction = signal_handler;
 167         sa.sa_flags = SA_RESTART|SA_SIGINFO;
 168
 169         pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
 170     }
 171
 172     n = (unsigned) pa_atomic_load(&read_lock);
 173     j = WHICH(n);
 174
 175     m = pa_xnew(pa_memtrap, 1);
 176     m->start = (void*) start;
 177     m->size = size;
 178     pa_atomic_store(&m->bad, 0);
 179
 180     memtrap_link(m, !j);
 181     memtrap_swap(n);
 182     memtrap_link(m, j);
 183
 184     pa_mutex_unlock(lock);
 185
 186     return m;
 187 }
 188
 189 void pa_memtrap_remove(pa_memtrap *m) {
 190     unsigned n, j;
 191     pa_mutex *lock;
 192
 193     pa_assert(m);
 194
 195     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 196     pa_mutex_lock(lock);
 197
 198     n = (unsigned) pa_atomic_load(&read_lock);
 199     j = WHICH(n);
 200
 201     memtrap_unlink(m, !j);
 202     memtrap_swap(n);
 203     memtrap_unlink(m, j);
 204
 205     pa_xfree(m);
 206
 207     if (!memtraps[0]) {
 208         struct sigaction sa;
 209
 210         memset(&sa, 0, sizeof(sa));
 211         sa.sa_handler = SIG_DFL;
 212         pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
 213     }
 214
 215     pa_mutex_unlock(lock);
 216 }
 217
 218 pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size) {
 219     unsigned n, j;
 220     pa_mutex *lock;
 221
 222     pa_assert(m);
 223
 224     pa_assert(start);
 225     pa_assert(size > 0);
 226     pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
 227     pa_assert(PA_PAGE_ALIGN(size) == size);
 228
 229     lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
 230     pa_mutex_lock(lock);
 231
 232     if (m->start == start && m->size == size)
 233         goto unlock;
 234
 235     n = (unsigned) pa_atomic_load(&read_lock);
 236     j = WHICH(n);
 237
 238     memtrap_unlink(m, !j);
 239     memtrap_swap(n);
 240     memtrap_unlink(m, j);
 241
 242     m->start = (void*) start;
 243     m->size = size;
 244     pa_atomic_store(&m->bad, 0);
 245
 246     n = (unsigned) pa_atomic_load(&read_lock);
 247     j = WHICH(n);
 248
 249     memtrap_link(m, !j);
 250     memtrap_swap(n);
 251     memtrap_link(m, j);
 252
 253 unlock:
 254     pa_mutex_unlock(lock);
 255
 256     return m;
 257 }