loader: Prevent deadlock using tab completion.

If tab completion using ast_module_helper is attempted
during startup, deadlock will ensue because the CLI
will attempt to lock the module list while it is already
locked by the loader. This causes deadlock because when
the loader tries to acquire the CLI lock, they are blocked
on each other.

Waiting for startup to complete is not feasible because
the CLI lock is acquired while waiting, so deadlock will
ensure regardless of whether or not a lock on the module
list is attempted.

To prevent deadlock, we immediately abort if tab completion
is attempted on the module list before Asterisk is fully
booted.

ASTERISK-30039 #close

Change-Id: Idd468906c512bb196631e366a8f597a0e2e9271d

include/asterisk/module.h

@@ -283,7 +283,7 @@ int ast_loader_unregister(int (*updater)(void));
  * \param type The type of action that will be performed by CLI.
  *
  * \retval A possible completion of the partial match.
- * \retval NULL if no matches were found.
+ * \retval NULL if no matches were found or Asterisk is not yet fully booted.
  */
 char *ast_module_helper(const char *line, const char *word, int pos, int state, int rpos, enum ast_module_helper_type type);
 

main/loader.c

@@ -1382,6 +1382,11 @@ char *ast_module_helper(const char *line, const char *word, int pos, int state,
 		return NULL;
 	}
 
+	/* Tab completion can't be used during startup, or CLI and loader will deadlock. */
+	if (!ast_test_flag(&ast_options, AST_OPT_FLAG_FULLY_BOOTED)) {
+		return NULL;
+	}
+
 	if (type == AST_MODULE_HELPER_LOAD) {
 		module_load_helper(word);