resolves deadlocks in chan_local

Issue_1.
In the local_hangup() 3 locks must be held at the same time... pvt, pvt->chan,
and pvt->owner.  Proper deadlock avoidance is done when the channel to hangup
is the outbound chan_local channel, but when it is not the outbound channel we
have an issue... We attempt to do deadlock avoidance only on the tech pvt, when
both the tech pvt and the pvt->owner are locked coming into that loop.  By
never giving up the pvt->owner channel deadlock avoidance is not entirely possible.
This patch resolves that by doing deadlock avoidance on both the pvt->owner and the pvt
when trying to get the pvt->chan lock.

Issue_2.
ast_prod() is used in ast_activate_generator() to queue a frame on the channel
and make the channel's read function get called.  This function is used in
ast_activate_generator() while the channel is locked, which mean's the channel
will have a lock both from the generator code and the frame_queue code by the
time it gets to chan_local.c's local_queue_frame code... local_queue_frame
contains some of the same crazy deadlock avoidance that local_hangup requires,
and this recursive lock prevents that deadlock avoidance from happening correctly.
This patch removes ast_prod() from the channel lock so only one lock is held during
the local_queue_frame function.

(closes issue #17185)
Reported by: schmoozecom
Patches:
      issue_17185_v1.diff uploaded by dvossel (license 671)
      issue_17185_v2.diff uploaded by dvossel (license 671)
Tested by: schmoozecom, GameGamer43

Review: https://reviewboard.asterisk.org/r/631/



git-svn-id: http://svn.digium.com/svn/asterisk/branches/1.4@259858 f38db490-d61c-443f-a65b-d21fe96a405b

2 files changed, 16 insertions, 10 deletions

diff --git a/channels/chan_local.c b/channels/chan_local.c
index d5441d047..e705ee582 100644
--- a/channels/chan_local.c
+++ b/channels/chan_local.c
@@ -543,12 +543,12 @@ static int local_hangup(struct ast_channel *ast)
 			/* Deadlock avoidance */
 			while (p->owner && ast_channel_trylock(p->owner)) {
 				ast_mutex_unlock(&p->lock);
-				if (ast) {
-					ast_channel_unlock(ast);
+				if (p->chan) {
+					ast_channel_unlock(p->chan);
 				}
 				usleep(1);
-				if (ast) {
-					ast_channel_lock(ast);
+				if (p->chan) {
+					ast_channel_lock(p->chan);
 				}
 				ast_mutex_lock(&p->lock);
 			}
@@ -563,8 +563,17 @@ static int local_hangup(struct ast_channel *ast)
 	} else {
 		ast_module_user_remove(p->u_owner);
 		while (p->chan && ast_channel_trylock(p->chan)) {
-			DEADLOCK_AVOIDANCE(&p->lock);
+				ast_mutex_unlock(&p->lock);
+				if (p->owner) {
+					ast_channel_unlock(p->owner);
+				}
+				usleep(1);
+				if (p->owner) {
+					ast_channel_lock(p->owner);
+				}
+				ast_mutex_lock(&p->lock);
 		}
+
 		p->owner = NULL;
 		if (p->chan) {
 			ast_queue_hangup(p->chan);
diff --git a/main/channel.c b/main/channel.c
index 752911b59..c6ba4fd7b 100644
--- a/main/channel.c
+++ b/main/channel.c
@@ -1708,25 +1708,22 @@ int ast_activate_generator(struct ast_channel *chan, struct ast_generator *gen,
 	int res = 0;
 
 	ast_channel_lock(chan);
-
 	if (chan->generatordata) {
 		if (chan->generator && chan->generator->release)
 			chan->generator->release(chan, chan->generatordata);
 		chan->generatordata = NULL;
 	}
-
-	ast_prod(chan);
 	if (gen->alloc && !(chan->generatordata = gen->alloc(chan, params))) {
 		res = -1;
 	}
-	
 	if (!res) {
 		ast_settimeout(chan, 160, generator_force, chan);
 		chan->generator = gen;
 	}
-
 	ast_channel_unlock(chan);
 
+	ast_prod(chan);
+
 	return res;
 }