fc77efbcd7
mode_set_fallback() schedules a call to mode_set_fallback_feedback_idle(), but it is possible for Mutter to repaint before the idle callbacks are dispatched. If that happens, mode_set_fallback_feedback_idle() does not get called before Mutter enters wait_for_pending_flips(), leading to a deadlock. Add the needed interfaces so that meta_kms_device_dispatch_sync() can flush all the implementation idle callbacks before it checks if any "events" are available. This prevents the deadlock by ensuring mode_set_fallback_feedback_idle() does get called before potentially waiting for actual DRM events. Presumably this call would not be needed if the implementation was running in its own thread, since it would eventually dispatch its idle callbacks before going to sleep polling on the DRM fd. This call might even be unnecessary overhead in that case, synchronizing with the implementation thread needlessly. But the thread does not exist yet, so this is needed for now. This is part 1 of 2 fixing a complete desktop freeze when drmModePageFlip() fails with EINVAL and the fallback to drmModeSetCrtc() succeeds but the success is not registered correctly as completed "flip". The freeze occurs under wait_for_pending_flips() which calls down into meta_kms_impl_device_dispatch() which ends up poll()'ing the DRM fd even though drmModeSetCrtc() will not produce a DRM event, hence the poll() never returns. The freeze was observed when hotplugging a DisplayLink dock for the first time on Ubuntu 19.10. CC stable: gnome-3-34 https://gitlab.gnome.org/GNOME/mutter/merge_requests/953 (cherry picked from commit 79491df2b8d90af3011d6a3a29b0d63ad52677f8)
Mutter
Mutter is a Wayland display server and X11 window manager and compositor library.
When used as a Wayland display server, it runs on top of KMS and libinput. It implements the compositor side of the Wayland core protocol as well as various protocol extensions. It also has functionality related to running X11 applications using Xwayland.
When used on top of Xorg it acts as a X11 window manager and compositing manager.
It contains functionality related to, among other things, window management, window compositing, focus tracking, workspace management, keybindings and monitor configuration.
Internally it uses a fork of Cogl, a hardware acceleration abstraction library used to simplify usage of OpenGL pipelines, as well as a fork af Clutter, a scene graph and user interface toolkit.
Mutter is used by, for example, GNOME Shell, the GNOME core user interface, and by Gala, elementary OS's window manager. It can also be run standalone, using the command "mutter", but just running plain mutter is only intended for debugging purposes.
Contributing
To contribute, open merge requests at https://gitlab.gnome.org/GNOME/mutter.
The coding style used is primarily the GNU flavor of the GNOME coding
style
with some minor additions such as preferring stdint.h types over GLib
fundamental types, and a soft 80 character line limit. However, in general,
look at the file you're editing for inspiration.
Commit messages should follow the GNOME commit message guidelines. We require an URL to either an issue or a merge request in each commit.
License
Mutter is distributed under the terms of the GNU General Public License, version 2 or later. See the COPYING file for detalis.