Merge pull request #2726 from taegyunkim/lazy-atexit

fix: install atexit handlers after apps are initialized

When --lazy or --lazy-apps is set, uwsgi's atexit() handlers, for Python it is uwsgi_python_atexit(), are installed in master process before calling fork(), and when worker loads the application, destructors for static global variables used in Python native extension modules are installed via atexit().

Those static global variables are destructed first and uwsgi atexit() handlers are run.

An application can install Python atexit handler via following two ways

    uwsgi Python module's atexit attribute, which will be called by uwsgi_python_atexit() here.
    using Python atexit module, which will be called by CPython Py_Finalize(), and uwsgi calls Py_Finalize() also from uwsgi_python_atexit() from here

For both cases, setting --lazy or --lazy-apps changes the order atexit() handlers are installed.

So, if the Python atexit function installed with either of the method calls into native extension module using global states, it results in an undefined behavior leading to segmentation faults.

Author: xrmx

core/uwsgi.c

@@ -3202,13 +3202,12 @@ int uwsgi_start(void *v_argv) {
 	//init apps hook (if not lazy)
 	if (!uwsgi.lazy && !uwsgi.lazy_apps) {
 		uwsgi_init_all_apps();
+		// Register uwsgi atexit plugin callbacks after all applications have
+		// been loaded. This ensures plugin atexit callbacks are called prior
+		// to application registered atexit callbacks.
+		atexit(uwsgi_plugins_atexit);
 	}
 
-	// Register uwsgi atexit plugin callbacks after all applications have
-	// been loaded. This ensures plugin atexit callbacks are called prior
-	// to application registered atexit callbacks.
-	atexit(uwsgi_plugins_atexit);
-
 	if (!uwsgi.master_as_root) {
 		uwsgi_log("dropping root privileges after application loading\n");
 		uwsgi_as_root();
@@ -3553,6 +3552,11 @@ void uwsgi_worker_run() {
 
 	if (uwsgi.lazy || uwsgi.lazy_apps) {
 		uwsgi_init_all_apps();
+
+		// Register uwsgi atexit plugin callbacks after all applications have
+		// been loaded. This ensures plugin atexit callbacks are called prior
+		// to application registered atexit callbacks.
+		atexit(uwsgi_plugins_atexit);
 	}
 
 	// some apps could be mounted only on specific workers