chan_sip: Address runaway when realtime peers subscribe to mailboxes

Users upgrading from asterisk 13.5 to a later version and who use
realtime with peers that have mailboxes were experiencing runaway
situations that manifested as a continuous stream of taskprocessor
congestion errors, memory leaks and an unresponsive chan_sip.

A related issue was that setting rtcachefriends=no NEVER worked in
asterisk 13 (since the move to stasis).  In 13.5 and earlier, when a
peer tried to register, all of the stasis threads would block and
chan_sip would again become unresponsive.  After 13.5, the runaway
would happen.

There were a number of causes...
* mwi_event_cb was (indirectly) calling build_peer even though calls to
  mwi_event_cb are often caused by build_peer.
* In an effort to prevent chan_sip from being unloaded while messages
  were still in flight, destroy_mailboxes was calling
  stasis_unsubscribe_and_join but in some cases waited forever for the
  final message.
* add_peer_mailboxes wasn't properly marking the existing mailboxes
  on a peer as "keep" so build_peer would always delete them all.
* add_peer_mwi_subs was unsubscribing existing mailbox subscriptions
  then just creating them again.

All of this was causing a flood of subscribes and unsubscribes on
multiple threads all for the same peer and mailbox.

Fixes...
* add_peer_mailboxes now marks mailboxes correctly and build_peer only
  deletes the ones that really are no longer needed by the peer.
* add_peer_mwi_subs now only adds subscriptions marked as "new" instead
  of unsubscribing and resubscribing everything.  It also adds the peer
  object's address to the mailbox instead of its name to the subscription
  userdata so mwi_event_cb doesn't have to call build_peer.

With these changes, with rtcachefriends=yes (the most common setting),
there are no leaks, locks, loops or crashes at shutdown.

rtcachefriends=no still causes leaks but at least it doesn't lock, loop
or crash.  Since making rtcachefriends=no work wasnt in scope for this
issue, further work will have to be deferred to a separate patch.

Side fixes...
 * The ast_lock_track structure had a member named "thread" which gdb
   doesn't like since it conflicts with it's "thread" command.  That
   member was renamed to "thread_id".

ASTERISK-25468 #close

Change-Id: I07519ef7f092629e1e844f855abd279d6475cdd0

2 files changed, 48 insertions, 20 deletions

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 51a08690e..31b70281d 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -1277,6 +1277,7 @@ static void mwi_event_cb(void *, struct stasis_subscription *, struct stasis_mes
 static void network_change_stasis_cb(void *data, struct stasis_subscription *sub, struct stasis_message *message);
 static void acl_change_stasis_cb(void *data, struct stasis_subscription *sub, struct stasis_message *message);
 static void sip_keepalive_all_peers(void);
+#define peer_in_destruction(peer) (ao2_ref(peer, 0) == 0)
 
 /*--- Applications, functions, CLI and manager command helpers */
 static const char *sip_nat_mode(const struct sip_pvt *p);
@@ -5197,13 +5198,24 @@ static void destroy_mailbox(struct sip_mailbox *mailbox)
 	ast_free(mailbox);
 }
 
+#define REMOVE_MAILBOX_WITH_LOCKED_PEER(__peer) \
+({\
+	struct sip_mailbox *__mailbox;\
+	ao2_lock(__peer);\
+	__mailbox = AST_LIST_REMOVE_HEAD(&(__peer->mailboxes), entry);\
+	ao2_unlock(__peer);\
+	__mailbox;\
+})
+
 /*! Destroy all peer-related mailbox subscriptions */
 static void clear_peer_mailboxes(struct sip_peer *peer)
 {
 	struct sip_mailbox *mailbox;
 
-	while ((mailbox = AST_LIST_REMOVE_HEAD(&peer->mailboxes, entry)))
+	/* Lock the peer while accessing/updating the linked list but NOT while destroying the mailbox */
+	while ((mailbox = REMOVE_MAILBOX_WITH_LOCKED_PEER(peer))) {
 		destroy_mailbox(mailbox);
+	}
 }
 
 static void sip_destroy_peer_fn(void *peer)
@@ -17195,19 +17207,21 @@ static void sip_peer_hold(struct sip_pvt *p, int hold)
 /*! \brief Receive MWI events that we have subscribed to */
 static void mwi_event_cb(void *userdata, struct stasis_subscription *sub, struct stasis_message *msg)
 {
-	char *peer_name = userdata;
-	struct sip_peer *peer = sip_find_peer(peer_name, NULL, TRUE, FINDALLDEVICES, FALSE, 0);
+	struct sip_peer *peer = userdata;
 
-	if (stasis_subscription_final_message(sub, msg)) {
-		/* peer can be non-NULL during reload. */
-		ao2_cleanup(peer);
-		ast_free(peer_name);
+	/*
+	 * peer can't be NULL here but the peer can be in the process of being
+	 * destroyed.  If it is, we don't want to send any messages.  In most cases,
+	 * the peer is actually gone and there's no sense sending NOTIFYs that will
+	 * never be answered.
+	 */
+	if (stasis_subscription_final_message(sub, msg) || peer_in_destruction(peer)) {
 		return;
 	}
-	if (peer && ast_mwi_state_type() == stasis_message_type(msg)) {
+
+	if (ast_mwi_state_type() == stasis_message_type(msg)) {
 		sip_send_mwi_to_peer(peer, 0);
 	}
-	ao2_cleanup(peer);
 }
 
 static void network_change_stasis_subscribe(void)
@@ -27932,15 +27946,14 @@ static void add_peer_mwi_subs(struct sip_peer *peer)
 
 	AST_LIST_TRAVERSE(&peer->mailboxes, mailbox, entry) {
 		struct stasis_topic *mailbox_specific_topic;
-		mailbox->event_sub = stasis_unsubscribe(mailbox->event_sub);
+
+		if (mailbox->status != SIP_MAILBOX_STATUS_NEW) {
+			continue;
+		}
 
 		mailbox_specific_topic = ast_mwi_topic(mailbox->id);
 		if (mailbox_specific_topic) {
-			char *peer_name = ast_strdup(peer->name);
-			if (!peer_name) {
-				return;
-			}
-			mailbox->event_sub = stasis_subscribe_pool(mailbox_specific_topic, mwi_event_cb, peer_name);
+			mailbox->event_sub = stasis_subscribe_pool(mailbox_specific_topic, mwi_event_cb, peer);
 		}
 	}
 }
@@ -29165,7 +29178,9 @@ static int get_cached_mwi(struct sip_peer *peer, int *new, int *old)
 }
 
 /*! \brief Send message waiting indication to alert peer that they've got voicemail
- *  \note Both peer and associated sip_pvt must be unlocked prior to calling this function
+ *  \note Both peer and associated sip_pvt must be unlocked prior to calling this function.
+ *  It's possible that this function will get called during peer destruction as final messages
+ *  are processed.  The peer will still be valid however.
  *  \returns -1 on failure, 0 on success
  */
 static int sip_send_mwi_to_peer(struct sip_peer *peer, int cache_only)
@@ -30988,6 +31003,7 @@ static void add_peer_mailboxes(struct sip_peer *peer, const char *value)
 		AST_LIST_TRAVERSE(&peer->mailboxes, mailbox, entry) {
 			if (!strcmp(mailbox->id, mbox)) {
 				duplicate = 1;
+				mailbox->status = SIP_MAILBOX_STATUS_EXISTING;
 				break;
 			}
 		}
@@ -31000,14 +31016,18 @@ static void add_peer_mailboxes(struct sip_peer *peer, const char *value)
 			continue;
 		}
 		strcpy(mailbox->id, mbox); /* SAFE */
+		mailbox->status = SIP_MAILBOX_STATUS_NEW;
+		mailbox->peer = peer;
 
 		AST_LIST_INSERT_TAIL(&peer->mailboxes, mailbox, entry);
 	}
 }
 
 /*! \brief Build peer from configuration (file or realtime static/dynamic) */
-static struct sip_peer *build_peer(const char *name, struct ast_variable *v, struct ast_variable *alt, int realtime, int devstate_only)
+static struct sip_peer *build_peer(const char *name, struct ast_variable *v_head, struct ast_variable *alt, int realtime, int devstate_only)
 {
+	/* We preserve the original value of v_head to make analyzing backtraces easier */
+	struct ast_variable *v = v_head;
 	struct sip_peer *peer = NULL;
 	struct ast_acl_list *oldacl = NULL;
 	struct ast_acl_list *olddirectmediaacl = NULL;
@@ -31071,6 +31091,7 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 			return NULL;
 		}
 
+
 		if (realtime && !ast_test_flag(&global_flags[1], SIP_PAGE2_RTCACHEFRIENDS)) {
 			ast_atomic_fetchadd_int(&rpeerobjs, 1);
 			ast_debug(3, "-REALTIME- peer built. Name: %s. Peer objects: %d\n", name, rpeerobjs);
@@ -31120,7 +31141,7 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 	if (!devstate_only) {
 		struct sip_mailbox *mailbox;
 		AST_LIST_TRAVERSE(&peer->mailboxes, mailbox, entry) {
-			mailbox->delme = 1;
+			mailbox->status = SIP_MAILBOX_STATUS_UNKNOWN;
 		}
 	}
 
@@ -31569,7 +31590,7 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 	if (!devstate_only) {
 		struct sip_mailbox *mailbox;
 		AST_LIST_TRAVERSE_SAFE_BEGIN(&peer->mailboxes, mailbox, entry) {
-			if (mailbox->delme) {
+			if (mailbox->status == SIP_MAILBOX_STATUS_UNKNOWN) {
 				AST_LIST_REMOVE_CURRENT(entry);
 				destroy_mailbox(mailbox);
 			}
diff --git a/channels/sip/include/sip.h b/channels/sip/include/sip.h
index 3e6832152..44c8ddf35 100644
--- a/channels/sip/include/sip.h
+++ b/channels/sip/include/sip.h
@@ -1230,6 +1230,12 @@ struct sip_pkt {
 	struct ast_str *data;
 };
 
+enum sip_mailbox_status {
+	SIP_MAILBOX_STATUS_UNKNOWN = 0,
+	SIP_MAILBOX_STATUS_EXISTING,
+	SIP_MAILBOX_STATUS_NEW,
+};
+
 /*!
  * \brief A peer's mailbox
  *
@@ -1240,7 +1246,8 @@ struct sip_mailbox {
 	/*! Associated MWI subscription */
 	struct stasis_subscription *event_sub;
 	AST_LIST_ENTRY(sip_mailbox) entry;
-	unsigned int delme:1;
+	struct sip_peer *peer;
+	enum sip_mailbox_status status;
 	char id[1];
 };