Remove some redundant locking code in ast_do_masquerade().

Also updated some comments.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@330368 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/main/channel.c b/main/channel.c
index b77e0f6007880a3e1b5b97fbfd1faa03c906da20..2022f63eb4bd2263d186df696210bb3848e9370c 100644 (file)
--- a/main/channel.c
+++ b/main/channel.c
@@ -6299,37 +6299,40 @@ int ast_do_masquerade(struct ast_channel *original)
         */
        ao2_lock(channels);
 
-       /* lock the original channel to determine if the masquerade is require or not */
+       /* lock the original channel to determine if the masquerade is required or not */
        ast_channel_lock(original);
 
-       /* This checks to see if the masquerade has already happened or not.  There is a
-        * race condition that exists for this function. Since all pvt and channel locks
-        * must be let go before calling do_masquerade, it is possible that it could be
-        * called multiple times for the same channel.  This check verifies whether
-        * or not the masquerade has already been completed by another thread */
-       if (!original->masq) {
-               ast_channel_unlock(original);
-               ao2_unlock(channels);
-               return 0; /* masq already completed by another thread, or never needed to be done to begin with */
-       }
-
-       /* now that we have verified no race condition exists, set the clone channel */
-       clonechan = original->masq;
-
-       /* since this function already holds the global container lock, unlocking original
-        * for deadlock avoidance will not result in any sort of masquerade race condition.
-        * If masq is called by a different thread while this happens, it will be stuck waiting
-        * until we unlock the container. */
+       /*
+        * This checks to see if the masquerade has already happened or
+        * not.  There is a race condition that exists for this
+        * function.  Since all pvt and channel locks must be let go
+        * before calling do_masquerade, it is possible that it could be
+        * called multiple times for the same channel.  This check
+        * verifies whether or not the masquerade has already been
+        * completed by another thread.
+        */
        while ((clonechan = original->masq) && ast_channel_trylock(clonechan)) {
+               /*
+                * A masq is needed but we could not get the clonechan lock
+                * immediately.  Since this function already holds the global
+                * container lock, unlocking original for deadlock avoidance
+                * will not result in any sort of masquerade race condition.  If
+                * masq is called by a different thread while this happens, it
+                * will be stuck waiting until we unlock the container.
+                */
                CHANNEL_DEADLOCK_AVOIDANCE(original);
        }
 
-       /* recheck if masq has been done the deadlock avoidance above could cause a double masq
-        * this is posible with at least ast_hangup*/
-       if (!original->masq) {
+       /*
+        * A final masq check must be done after deadlock avoidance for
+        * clonechan above or we could get a double masq.  This is
+        * posible with ast_hangup at least.
+        */
+       if (!clonechan) {
+               /* masq already completed by another thread, or never needed to be done to begin with */
                ast_channel_unlock(original);
                ao2_unlock(channels);
-               return 0; /* masq already completed by another thread, or never needed to be done to begin with */
+               return 0;
        }
 
        /* Get any transfer masquerade connected line exchange data. */