[Asterisk-code-review] contrib/systemd: Added note on common issues with systemd and asterisk (asterisk[master])

Mark Petersen asteriskteam at digium.com
Thu Jan 7 09:13:31 CST 2021


Attention is currently required from: Jaco Kroon.
Hello Jaco Kroon,

I'd like you to do a code review. Please visit

    https://gerrit.asterisk.org/c/asterisk/+/15308

to review the following change.


Change subject: contrib/systemd: Added note on common issues with systemd and asterisk
......................................................................

contrib/systemd: Added note on common issues with systemd and asterisk

With newer version of linux /var/run/ is a symlink to /run/ that has
been turned into tmpfs.

Added note that if asterisk has to bind to a specific IP that
systemd has to wait until the network is up.

Added note on how to make sure that the environment variable
HOSTNAME is included.

ASTERISK-29216
Reported by: Mark Petersen
Tested by: Mark Petersen

Change-Id: Ib3e560655befd3e99eec743687144f5569533379
---
M contrib/systemd/asterisk.service
M funcs/func_lock.c
2 files changed, 65 insertions(+), 109 deletions(-)



  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/08/15308/1

diff --git a/contrib/systemd/asterisk.service b/contrib/systemd/asterisk.service
index c3d4648..e654f50 100644
--- a/contrib/systemd/asterisk.service
+++ b/contrib/systemd/asterisk.service
@@ -1,15 +1,22 @@
 [Unit]
 Description=Asterisk PBX and telephony daemon.
 After=network.target
+#include these if asterisk need to bind to a specific IP (other than 0.0.0.0)
+#Wants=network-online.target
+#After=network-online.target network.target
 
 [Service]
 Type=notify
 Environment=HOME=/var/lib/asterisk
+#if systemd do not provide hostname and you need to use ${ENV(HOSTNAME)}
+#Environment=HOSTNAME=%H
 WorkingDirectory=/var/lib/asterisk
 User=asterisk
 Group=asterisk
 ExecStart=/usr/sbin/asterisk -mqf -C /etc/asterisk/asterisk.conf
 ExecReload=/usr/sbin/asterisk -rx 'core reload'
+#if /var/run is a tmpfs, this will create /var/run/asterisk on start
+#RuntimeDirectory=asterisk
 
 #Nice=0
 #UMask=0002
diff --git a/funcs/func_lock.c b/funcs/func_lock.c
index acb5fc9..0726407 100644
--- a/funcs/func_lock.c
+++ b/funcs/func_lock.c
@@ -110,7 +110,6 @@
 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 = AST_PTHREADT_NULL;
 
 static const struct ast_datastore_info lock_info = {
 	.type = "MUTEX",
@@ -124,8 +123,8 @@
 	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;
+	/*! Count of waiting of requesters for the named lock */
+	unsigned int requesters;
 	/*! who owns us */
 	struct ast_channel *owner;
 	/*! name of the lock */
@@ -147,8 +146,11 @@
 	while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) {
 		/* Only unlock if we own the lock */
 		if (clframe->channel == clframe->lock_frame->owner) {
+			ast_mutex_lock(&clframe->lock_frame->mutex);
 			clframe->lock_frame->count = 0;
 			clframe->lock_frame->owner = NULL;
+			ast_cond_signal(&clframe->lock_frame->cond);
+			ast_mutex_unlock(&clframe->lock_frame->mutex);
 		}
 		ast_free(clframe);
 	}
@@ -173,54 +175,11 @@
 		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_cmp_cb(void *obj, void *arg, int flags)
-{
-	struct ast_channel *chan = obj, *cmp_args = arg;
-	return strcasecmp(ast_channel_name(chan), ast_channel_name(cmp_args)) ? 0 : CMP_MATCH;
-}
-
 static int get_lock(struct ast_channel *chan, char *lockname, int trylock)
 {
 	struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
@@ -290,17 +249,13 @@
 			AST_LIST_UNLOCK(&locklist);
 			return -1;
 		}
-		current->requesters = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_MUTEX, 0,
-			NULL, ast_channel_cmp_cb);
-		if (!current->requesters) {
-			ast_mutex_destroy(&current->mutex);
-			ast_cond_destroy(&current->cond);
-			ast_free(current);
-			AST_LIST_UNLOCK(&locklist);
-			return -1;
-		}
+		current->requesters = 0;
 		AST_LIST_INSERT_TAIL(&locklist, current, entries);
 	}
+	/* Add to requester list */
+	ast_mutex_lock(&current->mutex);
+	current->requesters++;
+	ast_mutex_unlock(&current->mutex);
 	AST_LIST_UNLOCK(&locklist);
 
 	/* Found lock or created one - now find or create the corresponding link in the channel */
@@ -337,44 +292,42 @@
 	 * the same amount, before we'll release this one.
 	 */
 	if (current->owner == chan) {
+		/* We're not a requester, we already have it */
+		ast_mutex_lock(&current->mutex);
+		current->requesters--;
+		ast_mutex_unlock(&current->mutex);
 		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(&current->mutex);
-	/* Add to requester list */
-	ao2_link(current->requesters, chan);
-	pthread_kill(broker_tid, SIGURG);
-	AST_LIST_UNLOCK(&locklist);
-
 	/* Wait up to three seconds from now for LOCK. */
 	now = ast_tvnow();
 	timeout.tv_sec = now.tv_sec + 3;
 	timeout.tv_nsec = now.tv_usec * 1000;
 
-	if (!current->owner
-		|| (!trylock
-			&& !(res = ast_cond_timedwait(&current->cond, &current->mutex, &timeout)))) {
-		res = 0;
+	ast_mutex_lock(&current->mutex);
+
+	res = 0;
+	while (!trylock && !res && current->owner) {
+		res = ast_cond_timedwait(&current->cond, &current->mutex, &timeout);
+	}
+	if (current->owner) {
+		/* timeout;
+		 * trylock; or
+		 * cond_timedwait failed.
+		 *
+		 * either way, we fail to obtain the lock.
+		 */
+		res = -1;
+	} else {
 		current->owner = chan;
 		current->count++;
-	} else {
-		res = -1;
+		res = 0;
 	}
 	/* Remove from requester list */
-	ao2_unlink(current->requesters, chan);
+	current->requesters--;
+	if (res && unloading)
+		ast_cond_signal(&current->cond);
 	ast_mutex_unlock(&current->mutex);
 
 	return res;
@@ -422,7 +375,10 @@
 	}
 
 	if (--clframe->lock_frame->count == 0) {
+		ast_mutex_lock(&clframe->lock_frame->mutex);
 		clframe->lock_frame->owner = NULL;
+		ast_cond_signal(&clframe->lock_frame->cond);
+		ast_mutex_unlock(&clframe->lock_frame->mutex);
 	}
 
 	ast_copy_string(buf, "1", len);
@@ -478,33 +434,33 @@
 	/* Module flag */
 	unloading = 1;
 
-	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->owner || ao2_container_count(current->requesters)) {
-			/* Put it back */
-			AST_LIST_INSERT_HEAD(&locklist, current, entries);
-			AST_LIST_UNLOCK(&locklist);
-			unloading = 0;
-			return -1;
-		}
-		ast_mutex_destroy(&current->mutex);
-		ao2_ref(current->requesters, -1);
-		ast_free(current);
-	}
-
-	/* No locks left, unregister functions */
+	/* Make it impossible for new requesters to be added
+	 * NOTE:  channels could already be in get_lock() */
 	ast_custom_function_unregister(&lock_function);
 	ast_custom_function_unregister(&trylock_function);
-	ast_custom_function_unregister(&unlock_function);
 
-	if (broker_tid != AST_PTHREADT_NULL) {
-		pthread_cancel(broker_tid);
-		pthread_kill(broker_tid, SIGURG);
-		pthread_join(broker_tid, NULL);
+	AST_LIST_LOCK(&locklist);
+	AST_LIST_TRAVERSE(&locklist, current, entries) {
+		ast_mutex_lock(&current->mutex);
+		while (current->owner || current->requesters) {
+			/* either the mutex is locked, or other parties are currently in get_lock,
+			 * we need to wait for all of those to clear first */
+			ast_cond_wait(&current->cond, &current->mutex);
+		}
+		ast_mutex_unlock(&current->mutex);
+		/* At this point we know:
+		 * 1. the lock has been released,
+		 * 2. there are no requesters (nor should any be able to sneak in).
+		 */
+		ast_mutex_destroy(&current->mutex);
+		ast_cond_destroy(&current->cond);
+		ast_free(current);
 	}
-
 	AST_LIST_UNLOCK(&locklist);
+	AST_LIST_HEAD_DESTROY(&locklist);
+
+	/* At this point we can safely stop access to UNLOCK */
+	ast_custom_function_unregister(&unlock_function);
 
 	return 0;
 }
@@ -515,13 +471,6 @@
 	res |= ast_custom_function_register_escalating(&trylock_function, AST_CFE_READ);
 	res |= ast_custom_function_register_escalating(&unlock_function, AST_CFE_READ);
 
-	if (ast_pthread_create_background(&broker_tid, NULL, lock_broker, NULL)) {
-		ast_log(LOG_ERROR, "Failed to start lock broker thread. Unloading func_lock module.\n");
-		broker_tid = AST_PTHREADT_NULL;
-		unload_module();
-		return AST_MODULE_LOAD_DECLINE;
-	}
-
 	return res;
 }
 

-- 
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Gerrit-Project: asterisk
Gerrit-Branch: master
Gerrit-Change-Id: Ib3e560655befd3e99eec743687144f5569533379
Gerrit-Change-Number: 15308
Gerrit-PatchSet: 1
Gerrit-Owner: Mark Petersen <bugs.digium.com at zombie.dk>
Gerrit-Reviewer: Jaco Kroon <jaco at uls.co.za>
Gerrit-Attention: Jaco Kroon <jaco at uls.co.za>
Gerrit-MessageType: newchange
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