Better way to get chan and pvt lock for issue ASTERISK-17431.

Redoes -r308945 for issue ASTERISK-17431 deadlock fix for
sip_set_udptl_peer() and sip_set_rtp_peer().

* Lock the channels in the defined order and avoid the need for a deadlock
avoidance loop.

* Lock the channel before getting the pointer to the private structure to
be sure that the pointer will not change due to a masquerade or channel
hangup.

* To preserve sanity, check that chan and p->owner are the same.  (Pointer
rearangements should not happen without the protection of locks because
bad things tend to happen otherwise.)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@326144 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -28088,24 +28088,22 @@ static int sip_set_udptl_peer(struct ast_channel *chan, struct ast_udptl *udptl)
 {
 	struct sip_pvt *p;
 
+	/* Lock the channel and the private safely. */
+	ast_channel_lock(chan);
 	p = chan->tech_pvt;
 	if (!p) {
+		ast_channel_unlock(chan);
 		return -1;
 	}
-	/*
-	 * Lock both the pvt and it's owner safely.
-	 */
 	sip_pvt_lock(p);
-	while (p->owner && ast_channel_trylock(p->owner)) {
+	if (p->owner != chan) {
-		sip_pvt_unlock(p);
+		/* I suppose it could be argued that if this happens it is a bug. */
-		usleep(1);
+		ast_debug(1, "The private is not owned by channel %s anymore.\n", chan->name);
-		sip_pvt_lock(p);
-	}
-
-	if (!p->owner) {
 		sip_pvt_unlock(p);
+		ast_channel_unlock(chan);
 		return 0;
 	}
+
 	if (udptl) {
 		ast_udptl_get_peer(udptl, &p->udptlredirip);
 	} else {
@@ -28124,8 +28122,8 @@ static int sip_set_udptl_peer(struct ast_channel *chan, struct ast_udptl *udptl)
 	}
 	/* Reset lastrtprx timer */
 	p->lastrtprx = p->lastrtptx = time(NULL);
-	ast_channel_unlock(p->owner);
 	sip_pvt_unlock(p);
+	ast_channel_unlock(chan);
 	return 0;
 }
 
@@ -28232,10 +28230,21 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
 	struct sip_pvt *p;
 	int changed = 0;
 
+	/* Lock the channel and the private safely. */
+	ast_channel_lock(chan);
 	p = chan->tech_pvt;
 	if (!p) {
+		ast_channel_unlock(chan);
 		return -1;
 	}
+	sip_pvt_lock(p);
+	if (p->owner != chan) {
+		/* I suppose it could be argued that if this happens it is a bug. */
+		ast_debug(1, "The private is not owned by channel %s anymore.\n", chan->name);
+		sip_pvt_unlock(p);
+		ast_channel_unlock(chan);
+		return 0;
+	}
 
 	/* Disable early RTP bridge  */
 	if ((instance || vinstance || tinstance) &&
@@ -28244,25 +28253,10 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
 			return 0;
 	}
 
-	/*
-	 * Lock both the pvt and it's owner safely.
-	 */
-	sip_pvt_lock(p);
-	while (p->owner && ast_channel_trylock(p->owner)) {
-		sip_pvt_unlock(p);
-		usleep(1);
-		sip_pvt_lock(p);
-	}
-
-	if (!p->owner) {
-		sip_pvt_unlock(p);
-		return 0;
-	}
-
 	if (p->alreadygone) {
 		/* If we're destroyed, don't bother */
-		ast_channel_unlock(p->owner);
 		sip_pvt_unlock(p);
+		ast_channel_unlock(chan);
 		return 0;
 	}
 
@@ -28270,8 +28264,8 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
 	   that are known to be behind a NAT, then stop the process now
 	*/
 	if (nat_active && !ast_test_flag(&p->flags[0], SIP_DIRECT_MEDIA_NAT)) {
-		ast_channel_unlock(p->owner);
 		sip_pvt_unlock(p);
+		ast_channel_unlock(chan);
 		return 0;
 	}
 
@@ -28313,8 +28307,8 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
 	}
 	/* Reset lastrtprx timer */
 	p->lastrtprx = p->lastrtptx = time(NULL);
-	ast_channel_unlock(p->owner);
 	sip_pvt_unlock(p);
+	ast_channel_unlock(chan);
 	return 0;
 }