ui/cocoa: Run qemu_init in the main thread

This work is based on:
https://patchew.org/QEMU/20220317125534.38706-1-philippe.mathieu.daude@gmail.com/

Simplify the initialization dance by running qemu_init() in the main
thread before the Cocoa event loop starts. The secondary thread only
runs only qemu_main_loop() and qemu_cleanup().

This fixes a case where addRemovableDevicesMenuItems() calls
qmp_query_block() while expecting the main thread to still hold
the BQL.

Overriding the code after calling qemu_init() is done by dynamically
replacing a function pointer variable, qemu_main when initializing
ui/cocoa, which unifies the static implementation of main() for
builds with ui/cocoa and ones without ui/cocoa.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20220819132756.74641-2-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

docs/devel/fuzzing.rst

@@ -287,8 +287,8 @@ select the fuzz target. Then, the qtest client is initialized. If the target
 requires qos, qgraph is set up and the QOM/LIBQOS modules are initialized.
 Then the QGraph is walked and the QEMU cmd_line is determined and saved.
 
-After this, the ``vl.c:qemu_main`` is called to set up the guest. There are
-target-specific hooks that can be called before and after qemu_main, for
+After this, the ``vl.c:main`` is called to set up the guest. There are
+target-specific hooks that can be called before and after main, for
 additional setup(e.g. PCI setup, or VM snapshotting).
 
 ``LLVMFuzzerTestOneInput``: Uses qtest/qos functions to act based on the fuzz

include/qemu-main.h

@@ -5,6 +5,7 @@
 #ifndef QEMU_MAIN_H
 #define QEMU_MAIN_H
 
-int qemu_main(int argc, char **argv, char **envp);
+int qemu_default_main(void);
+extern int (*qemu_main)(void);
 
 #endif /* QEMU_MAIN_H */

include/sysemu/sysemu.h

@@ -102,7 +102,7 @@ void qemu_boot_set(const char *boot_order, Error **errp);
 
 bool defaults_enabled(void);
 
-void qemu_init(int argc, char **argv, char **envp);
+void qemu_init(int argc, char **argv);
 int qemu_main_loop(void);
 void qemu_cleanup(void);
 

softmmu/main.c

@@ -30,20 +30,20 @@
 #include <SDL.h>
 #endif
 
-int qemu_main(int argc, char **argv, char **envp)
+int qemu_default_main(void)
 {
     int status;
 
-    qemu_init(argc, argv, envp);
     status = qemu_main_loop();
     qemu_cleanup();
 
     return status;
 }
 
-#ifndef CONFIG_COCOA
+int (*qemu_main)(void) = qemu_default_main;
+
 int main(int argc, char **argv)
 {
-    return qemu_main(argc, argv, NULL);
+    qemu_init(argc, argv);
+    return qemu_main();
 }
-#endif

softmmu/vl.c

@@ -2605,7 +2605,7 @@ void qmp_x_exit_preconfig(Error **errp)
     }
 }
 
-void qemu_init(int argc, char **argv, char **envp)
+void qemu_init(int argc, char **argv)
 {
     QemuOpts *opts;
     QemuOpts *icount_opts = NULL, *accel_opts = NULL;

tests/qtest/fuzz/fuzz.c

@@ -218,7 +218,7 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp)
         g_free(pretty_cmd_line);
     }
 
-    qemu_init(result.we_wordc, result.we_wordv, NULL);
+    qemu_init(result.we_wordc, result.we_wordv);
 
     /* re-enable the rcu atfork, which was previously disabled in qemu_init */
     rcu_enable_atfork();

ui/cocoa.m

@@ -100,13 +100,9 @@ static int cursor_hide = 1;
 static int left_command_key_enabled = 1;
 static bool swap_opt_cmd;
 
-static int gArgc;
-static char **gArgv;
 static bool stretch_video;
 static NSTextField *pauseLabel;
 
-static QemuSemaphore display_init_sem;
-static QemuSemaphore app_started_sem;
 static bool allow_events;
 
 static NSInteger cbchangecount = -1;
@@ -597,7 +593,7 @@ static CGEventRef handleTapEvent(CGEventTapProxy proxy, CGEventType type, CGEven
         /*
          * Don't try to tell QEMU about UI information in the application
          * startup phase -- we haven't yet registered dcl with the QEMU UI
-         * layer, and also trying to take the iothread lock would deadlock.
+         * layer.
          * When cocoa_display_init() does register the dcl, the UI layer
          * will call cocoa_switch(), which will call updateUIInfo, so
          * we don't lose any information here.
@@ -790,16 +786,6 @@ static CGEventRef handleTapEvent(CGEventTapProxy proxy, CGEventType type, CGEven
 
 - (bool) handleEvent:(NSEvent *)event
 {
-    if(!allow_events) {
-        /*
-         * Just let OSX have all events that arrive before
-         * applicationDidFinishLaunching.
-         * This avoids a deadlock on the iothread lock, which cocoa_display_init()
-         * will not drop until after the app_started_sem is posted. (In theory
-         * there should not be any such events, but OSX Catalina now emits some.)
-         */
-        return false;
-    }
     return bool_with_iothread_lock(^{
         return [self handleEventLocked:event];
     });
@@ -1287,8 +1273,6 @@ static CGEventRef handleTapEvent(CGEventTapProxy proxy, CGEventType type, CGEven
 {
     COCOA_DEBUG("QemuCocoaAppController: applicationDidFinishLaunching\n");
     allow_events = true;
-    /* Tell cocoa_display_init to proceed */
-    qemu_sem_post(&app_started_sem);
 }
 
 - (void)applicationWillTerminate:(NSNotification *)aNotification
@@ -1919,92 +1903,45 @@ static void cocoa_clipboard_request(QemuClipboardInfo *info,
 /*
  * The startup process for the OSX/Cocoa UI is complicated, because
  * OSX insists that the UI runs on the initial main thread, and so we
- * need to start a second thread which runs the vl.c qemu_main():
- *
- * Initial thread:                    2nd thread:
+ * need to start a second thread which runs the qemu_default_main():
  * in main():
- *  create qemu-main thread
- *  wait on display_init semaphore
- *                                    call qemu_main()
- *                                    ...
  *  in cocoa_display_init():
- *                                     post the display_init semaphore
- *                                     wait on app_started semaphore
+ *   assign cocoa_main to qemu_main
  *   create application, menus, etc
+ *  in cocoa_main():
+ *   create qemu-main thread
  *   enter OSX run loop
- * in applicationDidFinishLaunching:
- *  post app_started semaphore
- *                                     tell main thread to fullscreen if needed
- *                                    [...]
- *                                    run qemu main-loop
- *
- * We do this in two stages so that we don't do the creation of the
- * GUI application menus and so on for command line options like --help
- * where we want to just print text to stdout and exit immediately.
  */
 
 static void *call_qemu_main(void *opaque)
 {
     int status;
 
-    COCOA_DEBUG("Second thread: calling qemu_main()\n");
-    status = qemu_main(gArgc, gArgv, *_NSGetEnviron());
-    COCOA_DEBUG("Second thread: qemu_main() returned, exiting\n");
+    COCOA_DEBUG("Second thread: calling qemu_default_main()\n");
+    qemu_mutex_lock_iothread();
+    status = qemu_default_main();
+    qemu_mutex_unlock_iothread();
+    COCOA_DEBUG("Second thread: qemu_default_main() returned, exiting\n");
     [cbowner release];
     exit(status);
 }
 
-int main (int argc, char **argv) {
+static int cocoa_main()
+{
     QemuThread thread;
 
-    COCOA_DEBUG("Entered main()\n");
-    gArgc = argc;
-    gArgv = argv;
-
-    qemu_sem_init(&display_init_sem, 0);
-    qemu_sem_init(&app_started_sem, 0);
+    COCOA_DEBUG("Entered %s()\n", __func__);
 
+    qemu_mutex_unlock_iothread();
     qemu_thread_create(&thread, "qemu_main", call_qemu_main,
                        NULL, QEMU_THREAD_DETACHED);
 
-    COCOA_DEBUG("Main thread: waiting for display_init_sem\n");
-    qemu_sem_wait(&display_init_sem);
-    COCOA_DEBUG("Main thread: initializing app\n");
-
-    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
-
-    // Pull this console process up to being a fully-fledged graphical
-    // app with a menubar and Dock icon
-    ProcessSerialNumber psn = { 0, kCurrentProcess };
-    TransformProcessType(&psn, kProcessTransformToForegroundApplication);
-
-    [QemuApplication sharedApplication];
-
-    create_initial_menus();
-
-    /*
-     * Create the menu entries which depend on QEMU state (for consoles
-     * and removeable devices). These make calls back into QEMU functions,
-     * which is OK because at this point we know that the second thread
-     * holds the iothread lock and is synchronously waiting for us to
-     * finish.
-     */
-    add_console_menu_entries();
-    addRemovableDevicesMenuItems();
-
-    // Create an Application controller
-    QemuCocoaAppController *appController = [[QemuCocoaAppController alloc] init];
-    [NSApp setDelegate:appController];
-
     // Start the main event loop
     COCOA_DEBUG("Main thread: entering OSX run loop\n");
     [NSApp run];
-    COCOA_DEBUG("Main thread: left OSX run loop, exiting\n");
+    COCOA_DEBUG("Main thread: left OSX run loop, which should never happen\n");
 
-    [appController release];
-    [pool release];
-
-    return 0;
+    abort();
 }
 
 
@@ -2083,25 +2020,42 @@ static void cocoa_refresh(DisplayChangeListener *dcl)
 
 static void cocoa_display_init(DisplayState *ds, DisplayOptions *opts)
 {
+    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
+
     COCOA_DEBUG("qemu_cocoa: cocoa_display_init\n");
 
-    /* Tell main thread to go ahead and create the app and enter the run loop */
-    qemu_sem_post(&display_init_sem);
-    qemu_sem_wait(&app_started_sem);
-    COCOA_DEBUG("cocoa_display_init: app start completed\n");
+    qemu_main = cocoa_main;
+
+    // Pull this console process up to being a fully-fledged graphical
+    // app with a menubar and Dock icon
+    ProcessSerialNumber psn = { 0, kCurrentProcess };
+    TransformProcessType(&psn, kProcessTransformToForegroundApplication);
+
+    [QemuApplication sharedApplication];
+
+    create_initial_menus();
+
+    /*
+     * Create the menu entries which depend on QEMU state (for consoles
+     * and removeable devices). These make calls back into QEMU functions,
+     * which is OK because at this point we know that the second thread
+     * holds the iothread lock and is synchronously waiting for us to
+     * finish.
+     */
+    add_console_menu_entries();
+    addRemovableDevicesMenuItems();
+
+    // Create an Application controller
+    QemuCocoaAppController *controller = [[QemuCocoaAppController alloc] init];
+    [NSApp setDelegate:controller];
 
-    QemuCocoaAppController *controller = (QemuCocoaAppController *)[[NSApplication sharedApplication] delegate];
     /* if fullscreen mode is to be used */
     if (opts->has_full_screen && opts->full_screen) {
-        dispatch_async(dispatch_get_main_queue(), ^{
         [NSApp activateIgnoringOtherApps: YES];
         [controller toggleFullScreen: nil];
-        });
     }
     if (opts->u.cocoa.has_full_grab && opts->u.cocoa.full_grab) {
-        dispatch_async(dispatch_get_main_queue(), ^{
         [controller setFullGrab: nil];
-        });
     }
 
     if (opts->has_show_cursor && opts->show_cursor) {
@@ -2121,6 +2075,8 @@ static void cocoa_display_init(DisplayState *ds, DisplayOptions *opts)
     qemu_event_init(&cbevent, false);
     cbowner = [[QemuCocoaPasteboardTypeOwner alloc] init];
     qemu_clipboard_peer_register(&cbpeer);
+
+    [pool release];
 }
 
 static QemuDisplay qemu_display_cocoa = {