Index: /pjproject/trunk/pjsip/include/pjsip/sip_transaction.h
===================================================================
--- /pjproject/trunk/pjsip/include/pjsip/sip_transaction.h	(revision 5572)
+++ /pjproject/trunk/pjsip/include/pjsip/sip_transaction.h	(revision 5573)
@@ -180,4 +180,8 @@
  * is created by calling #pjsip_tsx_create_key() from an incoming message.
  *
+ * IMPORTANT: To prevent deadlock, application should use
+ * #pjsip_tsx_layer_find_tsx2() instead which only adds a reference to
+ * the transaction instead of locking it.
+ *
  * @param key	    The key string to find the transaction.
  * @param lock	    If non-zero, transaction will be locked before the
@@ -190,4 +194,19 @@
 PJ_DECL(pjsip_transaction*) pjsip_tsx_layer_find_tsx( const pj_str_t *key,
 						      pj_bool_t lock );
+
+/**
+ * Find a transaction with the specified key. The transaction key normally
+ * is created by calling #pjsip_tsx_create_key() from an incoming message.
+ *
+ * @param key	    The key string to find the transaction.
+ * @param add_ref   If non-zero, transaction's reference will be added
+ *		    by one before the function returns, to make sure that
+ * 		    it's not deleted by other threads.
+ *
+ * @return	    The matching transaction instance, or NULL if transaction
+ *		    can not be found.
+ */
+PJ_DECL(pjsip_transaction*) pjsip_tsx_layer_find_tsx2( const pj_str_t *key,
+						       pj_bool_t add_ref );
 
 /**
Index: /pjproject/trunk/pjsip/src/pjsip-ua/sip_inv.c
===================================================================
--- /pjproject/trunk/pjsip/src/pjsip-ua/sip_inv.c	(revision 5572)
+++ /pjproject/trunk/pjsip/src/pjsip-ua/sip_inv.c	(revision 5573)
@@ -3276,5 +3276,5 @@
     pjsip_tsx_create_key(rdata->tp_info.pool, &key, PJSIP_ROLE_UAS,
 			 pjsip_get_invite_method(), rdata);
-    invite_tsx = pjsip_tsx_layer_find_tsx(&key, PJ_TRUE);
+    invite_tsx = pjsip_tsx_layer_find_tsx2(&key, PJ_TRUE);
 
     if (invite_tsx == NULL) {
@@ -3325,5 +3325,5 @@
 
     if (invite_tsx)
-	pj_grp_lock_release(invite_tsx->grp_lock);
+	pj_grp_lock_dec_ref(invite_tsx->grp_lock);
 }
 
Index: /pjproject/trunk/pjsip/src/pjsip/sip_transaction.c
===================================================================
--- /pjproject/trunk/pjsip/src/pjsip/sip_transaction.c	(revision 5572)
+++ /pjproject/trunk/pjsip/src/pjsip/sip_transaction.c	(revision 5573)
@@ -642,6 +642,6 @@
  * Find a transaction.
  */
-PJ_DEF(pjsip_transaction*) pjsip_tsx_layer_find_tsx( const pj_str_t *key,
-						     pj_bool_t lock )
+static pjsip_transaction* find_tsx( const pj_str_t *key, pj_bool_t lock,
+				    pj_bool_t add_ref )
 {
     pjsip_transaction *tsx;
@@ -655,5 +655,5 @@
     /* Prevent the transaction to get deleted before we have chance to lock it.
      */
-    if (tsx && lock)
+    if (tsx)
         pj_grp_lock_add_ref(tsx->grp_lock);
     
@@ -667,10 +667,27 @@
     PJ_RACE_ME(5);
 
-    if (tsx && lock) {
-	pj_grp_lock_acquire(tsx->grp_lock);
-        pj_grp_lock_dec_ref(tsx->grp_lock);
+    if (tsx) {
+	if (lock)
+	    pj_grp_lock_acquire(tsx->grp_lock);
+
+        if (!add_ref)
+            pj_grp_lock_dec_ref(tsx->grp_lock);
     }
 
     return tsx;
+}
+
+
+PJ_DEF(pjsip_transaction*) pjsip_tsx_layer_find_tsx( const pj_str_t *key,
+						     pj_bool_t lock )
+{
+    return find_tsx(key, lock, PJ_FALSE);
+}
+
+
+PJ_DEF(pjsip_transaction*) pjsip_tsx_layer_find_tsx2( const pj_str_t *key,
+						      pj_bool_t add_ref )
+{
+    return find_tsx(key, PJ_FALSE, add_ref);
 }
 
Index: /pjproject/trunk/pjsip/src/pjsip/sip_ua_layer.c
===================================================================
--- /pjproject/trunk/pjsip/src/pjsip/sip_ua_layer.c	(revision 5572)
+++ /pjproject/trunk/pjsip/src/pjsip/sip_ua_layer.c	(revision 5573)
@@ -552,10 +552,10 @@
 
 	/* Lookup the INVITE transaction */
-	tsx = pjsip_tsx_layer_find_tsx(&key, PJ_TRUE);
+	tsx = pjsip_tsx_layer_find_tsx2(&key, PJ_TRUE);
 
 	/* We should find the dialog attached to the INVITE transaction */
 	if (tsx) {
 	    dlg = (pjsip_dialog*) tsx->mod_data[mod_ua.mod.id];
-	    pj_grp_lock_release(tsx->grp_lock);
+	    pj_grp_lock_dec_ref(tsx->grp_lock);
 
 	    /* Dlg may be NULL on some extreme condition
