Fix race condition for CEL LINKEDID_END event

This patch fixes to situations that could cause the CEL LINKEDID_END event to
be missed.

1) During a core stop gracefully, modules are unloaded when ast_active_channels
== 0. The LINKDEDID_END event fires during the channel destructor. This means
that occasionally, the cel_* module will be unloaded before the channel is
destroyed. It seemed generally useful to wait until the refcount of all
channels == 0 before unloading, so I added a channel counter and used it in the
shutdown code.

2) During a masquerade, ast_channel_change_linkedid is called. It calls
ast_cel_check_retire_linkedid which unrefs the linkedid in the linkedids
container in cel.c. It didn't ref the new linkedid. Now it does. 

Review: https://reviewboard.asterisk.org/r/1900/
........

Merged revisions 367292 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 367299 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@367309 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 13 insertions, 3 deletions

diff --git a/main/channel.c b/main/channel.c
index 2ccd18f3e..98b2f4403 100644
--- a/main/channel.c
+++ b/main/channel.c
@@ -94,6 +94,7 @@ struct ast_epoll_data {
 static int shutting_down;
 
 static int uniqueint;
+static int chancount;
 
 unsigned long global_fin, global_fout;
 
@@ -645,6 +646,11 @@ int ast_active_channels(void)
 	return channels ? ao2_container_count(channels) : 0;
 }
 
+int ast_undestroyed_channels(void)
+{
+	return ast_atomic_fetchadd_int(&chancount, 0);
+}
+
 /*! \brief Cancel a shutdown in progress */
 void ast_cancel_shutdown(void)
 {
@@ -1095,6 +1101,7 @@ __ast_channel_alloc_ap(int needqueue, int state, const char *cid_num, const char
 	ast_cdr_init(ast_channel_cdr(tmp), tmp);
 	ast_cdr_start(ast_channel_cdr(tmp));
 
+	ast_atomic_fetchadd_int(&chancount, +1);
 	ast_cel_report_event(tmp, AST_CEL_CHANNEL_START, NULL, NULL, NULL);
 
 	headp = ast_channel_varshead(tmp);
@@ -2302,6 +2309,7 @@ static void ast_channel_destructor(void *obj)
 	if (callid) {
 		ast_callid_unref(callid);
 	}
+	ast_atomic_fetchadd_int(&chancount, -1);
 }
 
 /*! \brief Free a dummy channel structure */
@@ -6357,15 +6365,17 @@ static const char *oldest_linkedid(const char *a, const char *b)
  *  see if the channel's old linkedid is now being retired */
 static void ast_channel_change_linkedid(struct ast_channel *chan, const char *linkedid)
 {
+	ast_assert(linkedid != NULL);
 	/* if the linkedid for this channel is being changed from something, check... */
-	if (!ast_strlen_zero(ast_channel_linkedid(chan)) && 0 != strcmp(ast_channel_linkedid(chan), linkedid)) {
-		ast_cel_check_retire_linkedid(chan);
+	if (ast_channel_linkedid(chan) && !strcmp(ast_channel_linkedid(chan), linkedid)) {
+		return;
 	}
 
+	ast_cel_check_retire_linkedid(chan);
 	ast_channel_linkedid_set(chan, linkedid);
+	ast_cel_linkedid_ref(linkedid);
 }
 
-
 /*!
   \brief Propagate the oldest linkedid between associated channels