Fix deadlock if peer is destroyed while sending MWI notice.

A dialog cannot be destroyed by the ao2_callback dialog_needdestroy
because of a deadlock between the dialogs container lock and the RWLOCK of
the events subscription list.

* Create dialogs_to_destroy container to hold dialogs that will be
destroyed.

* Ensure that the event subscription callback will never happen with an
invalid peer pointer by making the event callback removal the first thing
in the peer destructor callback.

NOTE: This particular deadlock will not happen with Asterisk 10, but some
of the changes still apply.

(closes issue ASTERISK-18747)
Reported by: Gregory Hinton Nietsky

Review: https://reviewboard.asterisk.org/r/1564/
........

Merged revisions 343577 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@343578 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index e099e21bf0fd1c1fc341b4148e10ce5f242213fb..6c936ed9656b68b8bf080a6f0169f42203d618d7 100644 (file)
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -2953,6 +2953,13 @@ static void *dialog_unlink_rtpcheck(struct sip_pvt *dialog)
        return NULL;
 }
 
+/*!
+ * \brief Unlink a dialog from the dialogs container, as well as any other places
+ * that it may be currently stored.
+ *
+ * \note A reference to the dialog must be held before calling this function, and this
+ * function does not release that reference.
+ */
 void dialog_unlink_all(struct sip_pvt *dialog)
 {
        struct sip_pkt *cp;
@@ -4587,9 +4594,18 @@ static void sip_destroy_peer_fn(void *peer)
 static void sip_destroy_peer(struct sip_peer *peer)
 {
        ast_debug(3, "Destroying SIP peer %s\n", peer->name);
-       if (peer->outboundproxy)
+
+       /*
+        * Remove any mailbox event subscriptions for this peer before
+        * we destroy anything.  An event subscription callback may be
+        * happening right now.
+        */
+       clear_peer_mailboxes(peer);
+
+       if (peer->outboundproxy) {
                ao2_ref(peer->outboundproxy, -1);
-       peer->outboundproxy = NULL;
+               peer->outboundproxy = NULL;
+       }
 
        /* Delete it, it needs to disappear */
        if (peer->call) {
@@ -4623,7 +4639,6 @@ static void sip_destroy_peer(struct sip_peer *peer)
        }
        if (peer->dnsmgr)
                ast_dnsmgr_release(peer->dnsmgr);
-       clear_peer_mailboxes(peer);
 
        if (peer->socket.tcptls_session) {
                ao2_ref(peer->socket.tcptls_session, -1);
@@ -17025,14 +17040,12 @@ static int dialog_checkrtp_cb(void *dialogobj, void *arg, int flags)
  * \brief Match dialogs that need to be destroyed
  *
  * \details This is used with ao2_callback to unlink/delete all dialogs that
- * are marked needdestroy. It will return CMP_MATCH for candidates, and they
- * will be unlinked.
+ * are marked needdestroy.
  *
  * \todo Re-work this to improve efficiency.  Currently, this function is called
  * on _every_ dialog after processing _every_ incoming SIP/UDP packet, or
  * potentially even more often when the scheduler has entries to run.
  */
-
 static int dialog_needdestroy(void *dialogobj, void *arg, int flags)
 {
        struct sip_pvt *dialog = dialogobj;