The xcb_connection_t instance that is used here comes from
XGetXCBConnection(), is created by XOpenDisplay(), and is owned by the
returned Display*. Calling xcb_disconnect() directly on it leads to
various use-after-frees during shutdown, as reported by valgrind. The
first one of the about 30 errors is:
Invalid read of size 4
at 0x71F2051: xcb_take_socket (in /usr/lib64/libxcb.so.1.1.0)
by 0x78551DD: ??? (in /usr/lib64/libX11.so.6.3.0)
by 0x7855A14: _XFlush (in /usr/lib64/libX11.so.6.3.0)
by 0x7858504: _XGetRequest (in /usr/lib64/libX11.so.6.3.0)
by 0x7838966: XFreeGC (in /usr/lib64/libX11.so.6.3.0)
by 0x783238B: XCloseDisplay (in /usr/lib64/libX11.so.6.3.0)
by 0x4E680C2: wlr_x11_backend_destroy (backend.c:333)
by 0x4E57E94: wlr_backend_destroy (backend.c:39)
by 0x4E629FB: multi_backend_destroy (backend.c:47)
by 0x4E62B5A: handle_display_destroy (backend.c:90)
by 0x50B7E9F: ??? (in /usr/lib64/libwayland-server.so.0.1.0)
by 0x50B8476: wl_display_destroy (in /usr/lib64/libwayland-server.so.0.1.0)
Address 0xc14dda0 is 0 bytes inside a block of size 21,152 free'd
at 0x4C2DD18: free (vg_replace_malloc.c:530)
by 0x4E680A5: wlr_x11_backend_destroy (backend.c:330)
by 0x4E57E94: wlr_backend_destroy (backend.c:39)
by 0x4E629FB: multi_backend_destroy (backend.c:47)
by 0x4E62B5A: handle_display_destroy (backend.c:90)
by 0x50B7E9F: ??? (in /usr/lib64/libwayland-server.so.0.1.0)
by 0x50B8476: wl_display_destroy (in /usr/lib64/libwayland-server.so.0.1.0)
by 0x40C54E: main (main.c:84)
Block was alloc'd at
at 0x4C2EA1E: calloc (vg_replace_malloc.c:711)
by 0x71F0C60: xcb_connect_to_fd (in /usr/lib64/libxcb.so.1.1.0)
by 0x71F4BD4: xcb_connect_to_display_with_auth_info (in /usr/lib64/libxcb.so.1.1.0)
by 0x7854AA1: _XConnectXCB (in /usr/lib64/libX11.so.6.3.0)
by 0x7845481: XOpenDisplay (in /usr/lib64/libX11.so.6.3.0)
by 0x4E681B6: wlr_x11_backend_create (backend.c:376)
by 0x4E580EE: wlr_backend_autocreate (backend.c:99)
by 0x40C27D: main (main.c:35)
Normally, one would expect this to crash during XCloseDisplay() when
xcb_disconnect() is called again and frees the same data again (glibc would
detect a double free). However, XCloseDisplay() tries to clean up some internal
caches first for which it has to send requests to the X11 server (e.g. the
XFreeGC() above). This fails since the file descriptor was already closed,
which causes an IO error. Xlib's _XDefaultIOError() handles this by printing an
error message and calling exit(1).
Thus, the only symptom of this problem was compositors exiting
mid-shutdown and printing an error message:
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 6 requests (6 known processed) with 0 events remaining.
Fixes: https://github.com/swaywm/wlroots/issues/745
Signed-off-by: Uli Schlachter <psychon@znc.in>
The backend destroy signal is emitted before the output_remove
signal is. When the destroy signal is emitted listeners remove
their output_remove listener, so the output_remove signal is never
received and listeners have an invalid output pointer.
The correct way to solve this would be to remove the output_remove
signal completely and use the wlr_output.events.destroy signal
instead. This isn't yet possible because wl_signal_emit is unsafe
and listeners cannot be removed in listeners.
This backports some changes to #319 to fix the screenshooter data
format. This also adds wlr_backend_get_renderer which will be
useful to support multiple renderers.
