Allow locks to be inherited through a masquerade without causing starvation.
authorTilghman Lesher <tilghman@meg.abyt.es>
Wed, 30 Sep 2009 04:32:36 +0000 (04:32 +0000)
committerTilghman Lesher <tilghman@meg.abyt.es>
Wed, 30 Sep 2009 04:32:36 +0000 (04:32 +0000)
(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

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@221044 65c4cc65-6c06-0410-ace0-fbb531ad65f3

funcs/func_lock.c

index 1d2f894..ef8ccfa 100644 (file)
 
 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 
+#include <signal.h>
+
 #include "asterisk/lock.h"
 #include "asterisk/file.h"
 #include "asterisk/channel.h"
 #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 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 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 @@ static void lock_free(void *data)
        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 @@ static void lock_free(void *data)
        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 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try)
                        return -1;
                }
 
-               strcpy((char *)current + sizeof(*current), lockname);
-               ast_mutex_init(&current->mutex);
+               strcpy(current->name, lockname); /* SAFE */
+               if ((res = ast_mutex_init(&current->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(&current->cond, NULL))) {
+                       ast_log(LOG_ERROR, "Unable to initialize condition variable: %s\n", strerror(res));
+                       ast_mutex_destroy(&current->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(&current->mutex);
+                       ast_cond_destroy(&current->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 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try)
        /* 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 (clframe->lock_frame == current) {
+                       break;
+               }
        }
 
-       if (save_clframe) {
-               clframe = save_clframe;
-       } else {
+       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 @@ static int get_lock(struct ast_channel *chan, char *lockname, int try)
 
                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(&current->mutex)) == 0)
-                               break;
-                       if (ast_tvdiff_ms(ast_tvnow(), start) > 3000)
-                               break; /* bail after 3 seconds of waiting */
-                       usleep(1);
-               }
-       } else {
-               /* If the channel doesn't have any locks so far, then there's no possible deadlock. */
-               res = try ? ast_mutex_trylock(&current->mutex) : ast_mutex_lock(&current->mutex);
+       /* 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;
        }
 
-       if (res == 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(&current->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(&current->cond, &current->mutex, &three_seconds)))) {
+               res = 0;
+               current->owner = chan;
                current->count++;
-               current->channel = chan;
+       } else {
+               res = -1;
        }
+       /* Remove from requester list */
+       ao2_unlink(current->requesters, chan);
+       ast_mutex_unlock(&current->mutex);
 
        return res;
 }
@@ -269,7 +377,7 @@ static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, ch
        /* 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 @@ static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, ch
                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 @@ static int unload_module(void)
        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 @@ static int unload_module(void)
                        return -1;
                }
                ast_mutex_destroy(&current->mutex);
+               ao2_ref(current->requesters, -1);
                ast_free(current);
        }
 
@@ -365,7 +471,12 @@ static int unload_module(void)
        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 @@ static int load_module(void)
        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;
 }