[svn-commits] tilghman: trunk r221044 - /trunk/funcs/func_lock.c
SVN commits to the Digium repositories
svn-commits at lists.digium.com
Tue Sep 29 23:32:42 CDT 2009
Author: tilghman
Date: Tue Sep 29 23:32:36 2009
New Revision: 221044
URL: http://svnview.digium.com/svn/asterisk?view=rev&rev=221044
Log:
Allow locks to be inherited through a masquerade without causing starvation.
(closes issue #14859)
Reported by: atis
Patches:
20090821__issue14859.diff.txt uploaded by tilghman (license 14)
20090925__issue14859__1.6.1.diff.txt uploaded by tilghman (license 14)
Tested by: atis, tilghman
Modified:
trunk/funcs/func_lock.c
Modified: trunk/funcs/func_lock.c
URL: http://svnview.digium.com/svn/asterisk/trunk/funcs/func_lock.c?view=diff&rev=221044&r1=221043&r2=221044
==============================================================================
--- trunk/funcs/func_lock.c (original)
+++ trunk/funcs/func_lock.c Tue Sep 29 23:32:36 2009
@@ -29,6 +29,8 @@
#include "asterisk.h"
ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include <signal.h>
#include "asterisk/lock.h"
#include "asterisk/file.h"
@@ -36,6 +38,8 @@
#include "asterisk/pbx.h"
#include "asterisk/module.h"
#include "asterisk/linkedlists.h"
+#include "asterisk/astobj2.h"
+#include "asterisk/utils.h"
/*** DOCUMENTATION
<function name="LOCK" language="en_US">
@@ -87,20 +91,26 @@
static AST_LIST_HEAD_STATIC(locklist, lock_frame);
static void lock_free(void *data);
+static void lock_fixup(void *data, struct ast_channel *oldchan, struct ast_channel *newchan);
static int unloading = 0;
+static pthread_t broker_tid = -1;
static struct ast_datastore_info lock_info = {
.type = "MUTEX",
.destroy = lock_free,
+ .chan_fixup = lock_fixup,
};
struct lock_frame {
AST_LIST_ENTRY(lock_frame) entries;
ast_mutex_t mutex;
+ ast_cond_t cond;
/*! count is needed so if a recursive mutex exits early, we know how many times to unlock it. */
unsigned int count;
+ /*! Container of requesters for the named lock */
+ struct ao2_container *requesters;
/*! who owns us */
- struct ast_channel *channel;
+ struct ast_channel *owner;
/*! name of the lock */
char name[0];
};
@@ -119,12 +129,9 @@
AST_LIST_LOCK(oldlist);
while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) {
/* Only unlock if we own the lock */
- if (clframe->channel == clframe->lock_frame->channel) {
- clframe->lock_frame->channel = NULL;
- while (clframe->lock_frame->count > 0) {
- clframe->lock_frame->count--;
- ast_mutex_unlock(&clframe->lock_frame->mutex);
- }
+ if (clframe->channel == clframe->lock_frame->owner) {
+ clframe->lock_frame->count = 0;
+ clframe->lock_frame->owner = NULL;
}
ast_free(clframe);
}
@@ -133,13 +140,84 @@
ast_free(oldlist);
}
+static void lock_fixup(void *data, struct ast_channel *oldchan, struct ast_channel *newchan)
+{
+ struct ast_datastore *lock_store = ast_channel_datastore_find(oldchan, &lock_info, NULL);
+ AST_LIST_HEAD(, channel_lock_frame) *list;
+ struct channel_lock_frame *clframe = NULL;
+
+ if (!lock_store) {
+ return;
+ }
+ list = lock_store->data;
+
+ AST_LIST_LOCK(list);
+ AST_LIST_TRAVERSE(list, clframe, list) {
+ if (clframe->lock_frame->owner == oldchan) {
+ clframe->lock_frame->owner = newchan;
+ }
+ /* We don't move requesters, because the thread stack is different */
+ clframe->channel = newchan;
+ }
+ AST_LIST_UNLOCK(list);
+}
+
+static void *lock_broker(void *unused)
+{
+ struct lock_frame *frame;
+ struct timespec forever = { 1000000, 0 };
+ for (;;) {
+ int found_requester = 0;
+
+ /* Test for cancel outside of the lock */
+ pthread_testcancel();
+ AST_LIST_LOCK(&locklist);
+
+ AST_LIST_TRAVERSE(&locklist, frame, entries) {
+ if (ao2_container_count(frame->requesters)) {
+ found_requester++;
+ ast_mutex_lock(&frame->mutex);
+ if (!frame->owner) {
+ ast_cond_signal(&frame->cond);
+ }
+ ast_mutex_unlock(&frame->mutex);
+ }
+ }
+
+ AST_LIST_UNLOCK(&locklist);
+ pthread_testcancel();
+
+ /* If there are no requesters, then wait for a signal */
+ if (!found_requester) {
+ nanosleep(&forever, NULL);
+ } else {
+ sched_yield();
+ }
+ }
+ /* Not reached */
+ return NULL;
+}
+
+static int ast_channel_hash_cb(const void *obj, const int flags)
+{
+ const struct ast_channel *chan = obj;
+ return ast_str_case_hash(chan->name);
+}
+
+static int ast_channel_cmp_cb(void *obj, void *arg, int flags)
+{
+ struct ast_channel *chan = obj, *cmp_args = arg;
+ return strcasecmp(chan->name, cmp_args->name) ? 0 : CMP_MATCH;
+}
+
static int get_lock(struct ast_channel *chan, char *lockname, int try)
{
struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
struct lock_frame *current;
- struct channel_lock_frame *clframe = NULL, *save_clframe = NULL;
+ struct channel_lock_frame *clframe = NULL;
AST_LIST_HEAD(, channel_lock_frame) *list;
- int res, count_channel_locks = 0;
+ int res = 0;
+ struct timespec three_seconds = { .tv_sec = 3 };
if (!lock_store) {
ast_debug(1, "Channel %s has no lock datastore, so we're allocating one.\n", chan->name);
@@ -184,8 +262,27 @@
return -1;
}
- strcpy((char *)current + sizeof(*current), lockname);
- ast_mutex_init(¤t->mutex);
+ strcpy(current->name, lockname); /* SAFE */
+ if ((res = ast_mutex_init(¤t->mutex))) {
+ ast_log(LOG_ERROR, "Unable to initialize mutex: %s\n", strerror(res));
+ ast_free(current);
+ AST_LIST_UNLOCK(&locklist);
+ return -1;
+ }
+ if ((res = ast_cond_init(¤t->cond, NULL))) {
+ ast_log(LOG_ERROR, "Unable to initialize condition variable: %s\n", strerror(res));
+ ast_mutex_destroy(¤t->mutex);
+ ast_free(current);
+ AST_LIST_UNLOCK(&locklist);
+ return -1;
+ }
+ if (!(current->requesters = ao2_container_alloc(1, ast_channel_hash_cb, ast_channel_cmp_cb))) {
+ ast_mutex_destroy(¤t->mutex);
+ ast_cond_destroy(¤t->cond);
+ ast_free(current);
+ AST_LIST_UNLOCK(&locklist);
+ return -1;
+ }
AST_LIST_INSERT_TAIL(&locklist, current, entries);
}
AST_LIST_UNLOCK(&locklist);
@@ -193,25 +290,19 @@
/* Found lock or created one - now find or create the corresponding link in the channel */
AST_LIST_LOCK(list);
AST_LIST_TRAVERSE(list, clframe, list) {
- if (clframe->lock_frame == current)
- save_clframe = clframe;
-
- /* Only count mutexes that we currently hold */
- if (clframe->lock_frame->channel == chan)
- count_channel_locks++;
- }
-
- if (save_clframe) {
- clframe = save_clframe;
- } else {
+ if (clframe->lock_frame == current) {
+ break;
+ }
+ }
+
+ if (!clframe) {
if (unloading) {
/* Don't bother */
AST_LIST_UNLOCK(list);
return -1;
}
- clframe = ast_calloc(1, sizeof(*clframe));
- if (!clframe) {
+ if (!(clframe = ast_calloc(1, sizeof(*clframe)))) {
ast_log(LOG_ERROR, "Unable to allocate channel lock frame. %sLOCK will fail.\n", try ? "TRY" : "");
AST_LIST_UNLOCK(list);
return -1;
@@ -219,31 +310,48 @@
clframe->lock_frame = current;
clframe->channel = chan;
- /* Count the lock just created */
- count_channel_locks++;
AST_LIST_INSERT_TAIL(list, clframe, list);
}
AST_LIST_UNLOCK(list);
- /* Okay, we have both frames, so now we need to try to lock the mutex. */
- if (count_channel_locks > 1) {
- struct timeval start = ast_tvnow();
- for (;;) {
- if ((res = ast_mutex_trylock(¤t->mutex)) == 0)
- break;
- if (ast_tvdiff_ms(ast_tvnow(), start) > 3000)
- break; /* bail after 3 seconds of waiting */
- usleep(1);
- }
+ /* If we already own the lock, then we're being called recursively.
+ * Keep track of how many times that is, because we need to unlock
+ * the same amount, before we'll release this one.
+ */
+ if (current->owner == chan) {
+ current->count++;
+ return 0;
+ }
+
+ /* Okay, we have both frames, so now we need to try to lock.
+ *
+ * Locking order: always lock locklist first. We need the
+ * locklist lock because the broker thread counts whether
+ * there are requesters with the locklist lock held, and we
+ * need to hold it, so that when we send our signal, below,
+ * to wake up the broker thread, it definitely will see that
+ * a requester exists at that point in time. Otherwise, we
+ * could add to the requesters after it has already seen that
+ * that lock is unoccupied and wait forever for another signal.
+ */
+ AST_LIST_LOCK(&locklist);
+ ast_mutex_lock(¤t->mutex);
+ /* Add to requester list */
+ ao2_link(current->requesters, chan);
+ pthread_kill(broker_tid, SIGURG);
+ AST_LIST_UNLOCK(&locklist);
+
+ if ((!current->owner) ||
+ (!try && !(res = ast_cond_timedwait(¤t->cond, ¤t->mutex, &three_seconds)))) {
+ res = 0;
+ current->owner = chan;
+ current->count++;
} else {
- /* If the channel doesn't have any locks so far, then there's no possible deadlock. */
- res = try ? ast_mutex_trylock(¤t->mutex) : ast_mutex_lock(¤t->mutex);
- }
-
- if (res == 0) {
- current->count++;
- current->channel = chan;
- }
+ res = -1;
+ }
+ /* Remove from requester list */
+ ao2_unlink(current->requesters, chan);
+ ast_mutex_unlock(¤t->mutex);
return res;
}
@@ -269,7 +377,7 @@
/* Find item in the channel list */
AST_LIST_LOCK(list);
AST_LIST_TRAVERSE(list, clframe, list) {
- if (clframe->lock_frame && clframe->lock_frame->channel == chan && strcmp(clframe->lock_frame->name, data) == 0) {
+ if (clframe->lock_frame && clframe->lock_frame->owner == chan && strcmp(clframe->lock_frame->name, data) == 0) {
break;
}
}
@@ -284,19 +392,16 @@
return 0;
}
- /* Decrement before we release, because if a channel is waiting on the
- * mutex, there's otherwise a race to alter count. */
- clframe->lock_frame->count--;
- /* If we get another lock, this one shouldn't count against us for deadlock avoidance. */
- clframe->lock_frame->channel = NULL;
- ast_mutex_unlock(&clframe->lock_frame->mutex);
+ if (--clframe->lock_frame->count == 0) {
+ clframe->lock_frame->owner = NULL;
+ }
ast_copy_string(buf, "1", len);
return 0;
}
static int lock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
-{
+{
if (chan)
ast_autoservice_start(chan);
@@ -349,7 +454,7 @@
AST_LIST_LOCK(&locklist);
while ((current = AST_LIST_REMOVE_HEAD(&locklist, entries))) {
/* If any locks are currently in use, then we cannot unload this module */
- if (current->channel) {
+ if (current->owner || ao2_container_count(current->requesters)) {
/* Put it back */
AST_LIST_INSERT_HEAD(&locklist, current, entries);
AST_LIST_UNLOCK(&locklist);
@@ -357,6 +462,7 @@
return -1;
}
ast_mutex_destroy(¤t->mutex);
+ ao2_ref(current->requesters, -1);
ast_free(current);
}
@@ -365,7 +471,12 @@
ast_custom_function_unregister(&trylock_function);
ast_custom_function_unregister(&unlock_function);
+ pthread_cancel(broker_tid);
+ pthread_kill(broker_tid, SIGURG);
+ pthread_join(broker_tid, NULL);
+
AST_LIST_UNLOCK(&locklist);
+
return 0;
}
@@ -374,6 +485,7 @@
int res = ast_custom_function_register(&lock_function);
res |= ast_custom_function_register(&trylock_function);
res |= ast_custom_function_register(&unlock_function);
+ ast_pthread_create_background(&broker_tid, NULL, lock_broker, NULL);
return res;
}
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