memtrap: add new logic to trap and handle SIGBUS

2 files changed, 294 insertions, 0 deletions

diff --git a/src/pulsecore/memtrap.c b/src/pulsecore/memtrap.c
new file mode 100644
index 00000000..ec9b137c
--- /dev/null
+++ b/src/pulsecore/memtrap.c
@@ -0,0 +1,256 @@
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2009 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2.1 of the
+  License, or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <signal.h>
+#include <sys/mman.h>
+
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/semaphore.h>
+#include <pulsecore/macro.h>
+#include <pulsecore/mutex.h>
+#include <pulsecore/core-util.h>
+
+#include "memtrap.h"
+
+struct pa_memtrap {
+    void *start;
+    size_t size;
+    pa_atomic_t bad;
+    pa_memtrap *next[2], *prev[2];
+};
+
+static pa_memtrap *memtraps[2] = { NULL, NULL };
+static pa_atomic_t read_lock = PA_ATOMIC_INIT(0);
+static pa_static_semaphore semaphore = PA_STATIC_SEMAPHORE_INIT;
+static pa_static_mutex write_lock = PA_STATIC_MUTEX_INIT;
+
+#define MSB (1U << (sizeof(unsigned)*8U-1))
+#define WHICH(n) (!!((n) & MSB))
+#define COUNTER(n) ((n) & ~MSB)
+
+pa_bool_t pa_memtrap_is_good(pa_memtrap *m) {
+    pa_assert(m);
+
+    return !pa_atomic_load(&m->bad);
+}
+
+static void sigsafe_error(const char *s) {
+    write(STDERR_FILENO, s, strlen(s));
+}
+
+static void signal_handler(int sig, siginfo_t* si, void *data) {
+    unsigned n, j;
+    pa_memtrap *m;
+    void *r;
+
+    /* Increase the lock counter */
+    n = (unsigned) pa_atomic_inc(&read_lock);
+
+    /* The uppermost bit tells us which list to look at */
+    j = WHICH(n);
+
+    /* When n is 0 we have about 2^31 threads running that
+     * all got a sigbus at the same time, oh my! */
+    pa_assert(COUNTER(n)+1 > 0);
+
+    for (m = memtraps[j]; m; m = m->next[j])
+        if (si->si_addr >= m->start &&
+            (uint8_t*) si->si_addr < (uint8_t*) m->start + m->size)
+            break;
+
+    if (!m)
+        goto fail;
+
+    pa_atomic_store(&m->bad, 1);
+
+    /* Remap anonymous memory into the bad segment */
+    if ((r = mmap(m->start, m->size, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_FIXED|MAP_PRIVATE, -1, 0)) == MAP_FAILED) {
+        sigsafe_error("mmap() failed.\n");
+        goto fail;
+    }
+
+    pa_assert(r == m->start);
+
+    pa_atomic_dec(&read_lock);
+
+    /* Post the semaphore */
+    pa_semaphore_post(pa_static_semaphore_get(&semaphore, 0));
+
+    return;
+
+fail:
+    pa_atomic_dec(&read_lock);
+    abort();
+}
+
+static void memtrap_swap(unsigned n) {
+
+    for (;;) {
+
+        /* If the read counter is > 0 wait; if it is 0 try to swap the lists */
+        if (COUNTER(n) > 0)
+            pa_semaphore_wait(pa_static_semaphore_get(&semaphore, 0));
+        else if (pa_atomic_cmpxchg(&read_lock, (int) n, (int) (n ^ MSB)))
+            break;
+
+        n = (unsigned) pa_atomic_load(&read_lock);
+    }
+}
+
+static void memtrap_link(pa_memtrap *m, unsigned j) {
+    pa_assert(m);
+
+    m->prev[j] = NULL;
+    m->next[j] = memtraps[j];
+    memtraps[j] = m;
+}
+
+static void memtrap_unlink(pa_memtrap *m, int j) {
+    pa_assert(m);
+
+    if (m->next[j])
+        m->next[j]->prev[j] = m->prev[j];
+
+    if (m->prev[j])
+        m->prev[j]->next[j] = m->next[j];
+    else
+        memtraps[j] = m->next[j];
+}
+
+pa_memtrap* pa_memtrap_add(const void *start, size_t size) {
+    pa_memtrap *m = NULL;
+    pa_mutex *lock;
+    unsigned n, j;
+
+    pa_assert(start);
+    pa_assert(size > 0);
+    pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
+    pa_assert(PA_PAGE_ALIGN(size) == size);
+
+    lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
+    pa_mutex_lock(lock);
+
+    if (!memtraps[0]) {
+        struct sigaction sa;
+
+        /* Before we install the signal handler, make sure the
+         * semaphore is valid so that the initialization of the
+         * semaphore doesn't have to happen from the signal handler */
+        pa_static_semaphore_get(&semaphore, 0);
+
+        memset(&sa, 0, sizeof(sa));
+        sa.sa_sigaction = signal_handler;
+        sa.sa_flags = SA_RESTART|SA_SIGINFO;
+
+        pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
+    }
+
+    n = (unsigned) pa_atomic_load(&read_lock);
+    j = WHICH(n);
+
+    m = pa_xnew(pa_memtrap, 1);
+    m->start = (void*) start;
+    m->size = size;
+    pa_atomic_store(&m->bad, 0);
+
+    memtrap_link(m, !j);
+    memtrap_swap(n);
+    memtrap_link(m, j);
+
+    pa_mutex_unlock(lock);
+
+    return m;
+}
+
+void pa_memtrap_remove(pa_memtrap *m) {
+    unsigned n, j;
+    pa_mutex *lock;
+
+    pa_assert(m);
+
+    lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
+    pa_mutex_lock(lock);
+
+    n = (unsigned) pa_atomic_load(&read_lock);
+    j = WHICH(n);
+
+    memtrap_unlink(m, !j);
+    memtrap_swap(n);
+    memtrap_unlink(m, j);
+
+    pa_xfree(m);
+
+    if (!memtraps[0]) {
+        struct sigaction sa;
+
+        memset(&sa, 0, sizeof(sa));
+        sa.sa_handler = SIG_DFL;
+        pa_assert_se(sigaction(SIGBUS, &sa, NULL) == 0);
+    }
+
+    pa_mutex_unlock(lock);
+}
+
+pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size) {
+    unsigned n, j;
+    pa_mutex *lock;
+
+    pa_assert(m);
+
+    pa_assert(start);
+    pa_assert(size > 0);
+    pa_assert(PA_PAGE_ALIGN_PTR(start) == start);
+    pa_assert(PA_PAGE_ALIGN(size) == size);
+
+    lock = pa_static_mutex_get(&write_lock, FALSE, FALSE);
+    pa_mutex_lock(lock);
+
+    if (m->start == start && m->size == size)
+        goto unlock;
+
+    n = (unsigned) pa_atomic_load(&read_lock);
+    j = WHICH(n);
+
+    memtrap_unlink(m, !j);
+    memtrap_swap(n);
+    memtrap_unlink(m, j);
+
+    m->start = (void*) start;
+    m->size = size;
+    pa_atomic_store(&m->bad, 0);
+
+    n = (unsigned) pa_atomic_load(&read_lock);
+    j = WHICH(n);
+
+    memtrap_link(m, !j);
+    memtrap_swap(n);
+    memtrap_link(m, j);
+
+unlock:
+    pa_mutex_unlock(lock);
+
+    return m;
+}
diff --git a/src/pulsecore/memtrap.h b/src/pulsecore/memtrap.h
new file mode 100644
index 00000000..d93d6720
--- /dev/null
+++ b/src/pulsecore/memtrap.h
@@ -0,0 +1,38 @@
+#ifndef foopulsecorememtraphfoo
+#define foopulsecorememtraphfoo
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2009 Lennart Poettering
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2.1 of the
+  License, or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#include <sys/types.h>
+
+#include <pulsecore/macro.h>
+
+typedef struct pa_memtrap pa_memtrap;
+
+pa_memtrap* pa_memtrap_add(const void *start, size_t size);
+pa_memtrap *pa_memtrap_update(pa_memtrap *m, const void *start, size_t size);
+
+void pa_memtrap_remove(pa_memtrap *m);
+
+pa_bool_t pa_memtrap_is_good(pa_memtrap *m);
+
+#endif