func_odbc: Fix connection deadlock.

The func_odbc module was modified to ensure that the
previous behavior of using a single database connection
was maintained. This was done by getting a single database
connection and holding on to it. With the new multiple
connection support in res_odbc this will actually starve
every other thread from getting access to the database as
it also maintains the previous behavior of having only
a single database connection.

This change disables the func_odbc specific behavior if
the res_odbc module is running with only a single database
connection active. The connection is only kept for the
duration of the request.

ASTERISK-26177 #close

Change-Id: I9bdbd8a300fb3233877735ad3fd07bce38115b7f

funcs/func_odbc.c

@@ -388,9 +388,25 @@ static struct odbc_obj *get_odbc_obj(const char *dsn_name, struct dsn **dsn)
 static inline void release_obj_or_dsn(struct odbc_obj **obj, struct dsn **dsn)
 {
 	if (dsn && *dsn) {
+		/* If multiple connections are not enabled then the guarantee
+		 * of a single connection already exists and holding on to the
+		 * connection would prevent any other user from acquiring it
+		 * indefinitely.
+		 */
+		if (ast_odbc_get_max_connections((*dsn)->name) < 2) {
+			ast_odbc_release_obj((*dsn)->connection);
+			(*dsn)->connection = NULL;
+		}
 		ao2_unlock(*dsn);
 		ao2_ref(*dsn, -1);
 		*dsn = NULL;
+		/* Some callers may provide both an obj and dsn. To ensure that
+		 * the connection is not released twice we set it to NULL here if
+		 * present.
+		 */
+		if (obj) {
+			*obj = NULL;
+		}
 	} else if (obj && *obj) {
 		ast_odbc_release_obj(*obj);
 		*obj = NULL;

include/asterisk/res_odbc.h

@@ -243,4 +243,9 @@ int ast_odbc_text2isolation(const char *txt);
  */
 const char *ast_odbc_isolation2text(int iso);
 
+/*!
+ * \brief Return the current configured maximum number of connections for a class
+ */
+unsigned int ast_odbc_get_max_connections(const char *name);
+
 #endif /* _ASTERISK_RES_ODBC_H */

res/res_odbc.c

@@ -744,6 +744,22 @@ static int aoro2_class_cb(void *obj, void *arg, int flags)
 	return 0;
 }
 
+unsigned int ast_odbc_get_max_connections(const char *name)
+{
+	struct odbc_class *class;
+	unsigned int max_connections;
+
+	class = ao2_callback(class_container, 0, aoro2_class_cb, (char *) name);
+	if (!class) {
+		return 0;
+	}
+
+	max_connections = class->maxconnections;
+	ao2_ref(class, -1);
+
+	return max_connections;
+}
+
 /*
  * \brief Determine if the connection has died.
  *