fix: avoid deadlocks in Python forked workers

core/master_utils.c

@@ -747,9 +747,22 @@ int uwsgi_respawn_worker(int wid) {
 		pthread_mutex_lock(&uwsgi.threaded_logger_lock);
 	}
 
+
+	for (i = 0; i < 256; i++) {
+		if (uwsgi.p[i]->pre_uwsgi_fork) {
+			uwsgi.p[i]->pre_uwsgi_fork();
+		}
+	}
+
 	pid_t pid = uwsgi_fork(uwsgi.workers[wid].name);
 
 	if (pid == 0) {
+		for (i = 0; i < 256; i++) {
+			if (uwsgi.p[i]->post_uwsgi_fork) {
+				uwsgi.p[i]->post_uwsgi_fork(1);
+			}
+		}
+
 		signal(SIGWINCH, worker_wakeup);
 		signal(SIGTSTP, worker_wakeup);
 		uwsgi.mywid = wid;
@@ -792,16 +805,6 @@ int uwsgi_respawn_worker(int wid) {
 
 		uwsgi.my_signal_socket = uwsgi.workers[wid].signal_pipe[1];
 
-		if (uwsgi.master_process) {
-			if ((uwsgi.workers[uwsgi.mywid].respawn_count || uwsgi.status.is_cheap)) {
-				for (i = 0; i < 256; i++) {
-					if (uwsgi.p[i]->master_fixup) {
-						uwsgi.p[i]->master_fixup(1);
-					}
-				}
-			}
-		}
-
 		if (uwsgi.threaded_logger) {
 			pthread_mutex_unlock(&uwsgi.threaded_logger_lock);
 		}
@@ -812,6 +815,12 @@ int uwsgi_respawn_worker(int wid) {
 		uwsgi_error("fork()");
 	}
 	else {
+		for (i = 0; i < 256; i++) {
+			if (uwsgi.p[i]->post_uwsgi_fork) {
+				uwsgi.p[i]->post_uwsgi_fork(0);
+			}
+		}
+
 		// the pid is set only in the master, as the worker should never use it
 		uwsgi.workers[wid].pid = pid;
 

core/mule.c

@@ -69,12 +69,6 @@ void uwsgi_mule(int id) {
 
 		uwsgi_close_all_sockets();
 
-		for (i = 0; i < 256; i++) {
-			if (uwsgi.p[i]->master_fixup) {
-				uwsgi.p[i]->master_fixup(1);
-			}
-		}
-
 		for (i = 0; i < 256; i++) {
 			if (uwsgi.p[i]->post_fork) {
 				uwsgi.p[i]->post_fork();

core/uwsgi.c

@@ -3338,14 +3338,6 @@ int uwsgi_start(void *v_argv) {
 		}
 	}
 
-	// master fixup
-	for (i = 0; i < 256; i++) {
-		if (uwsgi.p[i]->master_fixup) {
-			uwsgi.p[i]->master_fixup(0);
-		}
-	}
-
-
 
 	struct uwsgi_spooler *uspool = uwsgi.spoolers;
 	while (uspool) {

plugins/python/python_plugin.c

@@ -428,17 +428,14 @@ void uwsgi_python_atexit() {
 
 void uwsgi_python_post_fork() {
 
-	if (uwsgi.i_am_a_spooler) {
+	// Need to acquire the gil when no master process is used as first worker
+	// will not have been forked like others
+	if (!uwsgi.master_process && uwsgi.mywid == 1) {
 		UWSGI_GET_GIL
-	}	
+	}
 
-	// reset python signal flags so child processes can trap signals
-	if (up.call_osafterfork) {
-#ifdef HAS_NOT_PyOS_AfterFork_Child
-		PyOS_AfterFork();
-#else
-                PyOS_AfterFork_Child();
-#endif
+	if (uwsgi.i_am_a_spooler) {
+		UWSGI_GET_GIL
 	}
 
 	uwsgi_python_reset_random_seed();
@@ -1129,6 +1126,10 @@ void uwsgi_python_preinit_apps() {
 	up.loaders[LOADER_CALLABLE] = uwsgi_callable_loader;
 	up.loaders[LOADER_STRING_CALLABLE] = uwsgi_string_callable_loader;
 
+	// GIL was released in previous initialization steps but init_pyargv expects
+	// the GIL to be acquired
+	UWSGI_GET_GIL
+
 	init_pyargv();
 
         init_uwsgi_embedded_module();
@@ -1174,14 +1175,13 @@ void uwsgi_python_preinit_apps() {
 		upli = upli->next;
 	}
 
+	// Release the GIL before moving on forward with initialization
+	UWSGI_RELEASE_GIL
+
 }
 
 void uwsgi_python_init_apps() {
-
-	// lazy ?
-	if (uwsgi.mywid > 0) {
-		UWSGI_GET_GIL;
-	}
+	UWSGI_GET_GIL;
 
 	// prepare for stack suspend/resume
 	if (uwsgi.async > 0) {
@@ -1290,32 +1290,35 @@ void uwsgi_python_init_apps() {
 			Py_INCREF(up.after_req_hook_args);
 		}
 	}
-	// lazy ?
-	if (uwsgi.mywid > 0) {
-		UWSGI_RELEASE_GIL;
-	}
+	UWSGI_RELEASE_GIL;
 
 }
 
-void uwsgi_python_master_fixup(int step) {
 
-	static int master_fixed = 0;
-	static int worker_fixed = 0;
+void uwsgi_python_pre_uwsgi_fork() {
+	if (uwsgi.has_threads) {
+		// Acquire the gil and import lock before forking in order to avoid
+		// deadlocks in workers
+		UWSGI_GET_GIL
+		_PyImport_AcquireLock();
+	}
+}
 
-	if (!uwsgi.master_process) return;
 
+void uwsgi_python_post_uwsgi_fork(int step) {
 	if (uwsgi.has_threads) {
 		if (step == 0) {
-			if (!master_fixed) {
-				UWSGI_RELEASE_GIL;
-				master_fixed = 1;
-			}
-		}	
+			// Release locks within master process
+			_PyImport_ReleaseLock();
+			UWSGI_RELEASE_GIL
+		}
 		else {
-			if (!worker_fixed) {
-				UWSGI_GET_GIL;
-				worker_fixed = 1;
-			}
+			// Ensure thread state and locks are cleaned up in child process
+#ifdef HAS_NOT_PyOS_AfterFork_Child
+			PyOS_AfterFork();
+#else
+			PyOS_AfterFork_Child();
+#endif
 		}
 	}
 }
@@ -1349,7 +1352,8 @@ void uwsgi_python_enable_threads() {
 		up.reset_ts = threaded_reset_ts;
 	}
 
-
+	// Release the newly created gil from call to PyEval_InitThreads above
+	UWSGI_RELEASE_GIL
 
 	uwsgi_log("python threads support enabled\n");
 
@@ -2043,13 +2047,6 @@ static int uwsgi_python_worker() {
 	if (!up.worker_override)
 		return 0;
 	UWSGI_GET_GIL;
-	// ensure signals can be used again from python
-	if (!up.call_osafterfork)
-#ifdef HAS_NOT_PyOS_AfterFork_Child
-		PyOS_AfterFork();
-#else
-                PyOS_AfterFork_Child();
-#endif
 	FILE *pyfile = fopen(up.worker_override, "r");
 	if (!pyfile) {
 		uwsgi_error_open(up.worker_override);
@@ -2081,6 +2078,10 @@ struct uwsgi_plugin python_plugin = {
 	.alias = "python",
 	.modifier1 = 0,
 	.init = uwsgi_python_init,
+
+	.pre_uwsgi_fork = uwsgi_python_pre_uwsgi_fork,
+	.post_uwsgi_fork = uwsgi_python_post_uwsgi_fork,
+
 	.post_fork = uwsgi_python_post_fork,
 	.options = uwsgi_python_options,
 	.request = uwsgi_request_wsgi,
@@ -2090,7 +2091,6 @@ struct uwsgi_plugin python_plugin = {
 	.init_apps = uwsgi_python_init_apps,
 
 	.fixup = uwsgi_python_fixup,
-	.master_fixup = uwsgi_python_master_fixup,
 	.master_cycle = uwsgi_python_master_cycle,
 
 	.mount_app = uwsgi_python_mount_app,

plugins/python/uwsgi_python.h

@@ -1,5 +1,6 @@
 #include <uwsgi.h>
 #include <Python.h>
+#include <pythread.h>
 
 #include <frameobject.h>
 

uwsgi.h

@@ -1039,6 +1039,8 @@ struct uwsgi_plugin {
 	void *data;
 	void (*on_load) (void);
 	int (*init) (void);
+	void (*pre_uwsgi_fork) (void);
+	void (*post_uwsgi_fork) (int);
 	void (*post_init) (void);
 	void (*post_fork) (void);
 	struct uwsgi_option *options;