Olivier Fourdan authored Aug 08, 2016 and Adam Jackson committed Aug 15, 2016

At shutdown, the Xserver will free all its resources which includes the
RRCrtc and RROutput created.

Xwayland would do the same in its xwl_output_destroy() called from
xwl_close_screen(), leading to a double free of existing RRCrtc
RROutput:

 Invalid read of size 4
    at 0x4CDA10: RRCrtcDestroy (rrcrtc.c:689)
    by 0x426E75: xwl_output_destroy (xwayland-output.c:301)
    by 0x424144: xwl_close_screen (xwayland.c:117)
    by 0x460E17: CursorCloseScreen (cursor.c:187)
    by 0x4EB5A3: AnimCurCloseScreen (animcur.c:106)
    by 0x4EF431: present_close_screen (present_screen.c:64)
    by 0x556D40: dix_main (main.c:354)
    by 0x6F0D290: (below main) (in /usr/lib/libc-2.24.so)
  Address 0xbb1fc30 is 0 bytes inside a block of size 728 free'd
    at 0x4C2BDB0: free (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    by 0x4CCE5F: RRCrtcDestroyResource (rrcrtc.c:719)
    by 0x577541: doFreeResource (resource.c:895)
    by 0x5787B5: FreeClientResources (resource.c:1161)
    by 0x578862: FreeAllResources (resource.c:1176)
    by 0x556C54: dix_main (main.c:323)
    by 0x6F0D290: (below main) (in /usr/lib/libc-2.24.so)
  Block was alloc'd at
    at 0x4C2CA6A: calloc (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    by 0x4CC6DB: RRCrtcCreate (rrcrtc.c:76)
    by 0x426D1C: xwl_output_create (xwayland-output.c:264)
    by 0x4232EC: registry_global (xwayland.c:431)
    by 0x76CB1C7: ffi_call_unix64 (in /usr/lib/libffi.so.6.0.4)
    by 0x76CAC29: ffi_call (in /usr/lib/libffi.so.6.0.4)
    by 0x556CEFD: wl_closure_invoke (connection.c:935)
    by 0x5569CBF: dispatch_event.isra.4 (wayland-client.c:1310)
    by 0x556AF13: dispatch_queue (wayland-client.c:1456)
    by 0x556AF13: wl_display_dispatch_queue_pending
(wayland-client.c:1698)
    by 0x556B33A: wl_display_roundtrip_queue (wayland-client.c:1121)
    by 0x42371C: xwl_screen_init (xwayland.c:631)
    by 0x552F60: AddScreen (dispatch.c:3864)

And:

 Invalid read of size 4
    at 0x522890: RROutputDestroy (rroutput.c:348)
    by 0x42684E: xwl_output_destroy (xwayland-output.c:302)
    by 0x423CF4: xwl_close_screen (xwayland.c:118)
    by 0x4B6377: CursorCloseScreen (cursor.c:187)
    by 0x539503: AnimCurCloseScreen (animcur.c:106)
    by 0x53D081: present_close_screen (present_screen.c:64)
    by 0x43DBF0: dix_main (main.c:354)
    by 0x7068730: (below main) (libc-start.c:289)
  Address 0xc403190 is 0 bytes inside a block of size 154 free'd
    at 0x4C2CD5A: free (vg_replace_malloc.c:530)
    by 0x521DF3: RROutputDestroyResource (rroutput.c:389)
    by 0x45DA61: doFreeResource (resource.c:895)
    by 0x45ECFD: FreeClientResources (resource.c:1161)
    by 0x45EDC2: FreeAllResources (resource.c:1176)
    by 0x43DB04: dix_main (main.c:323)
    by 0x7068730: (below main) (libc-start.c:289)
  Block was alloc'd at
    at 0x4C2BBAD: malloc (vg_replace_malloc.c:299)
    by 0x52206B: RROutputCreate (rroutput.c:84)
    by 0x426763: xwl_output_create (xwayland-output.c:270)
    by 0x422EDC: registry_global (xwayland.c:432)
    by 0x740FC57: ffi_call_unix64 (unix64.S:76)
    by 0x740F6B9: ffi_call (ffi64.c:525)
    by 0x5495A9D: wl_closure_invoke (connection.c:949)
    by 0x549283F: dispatch_event.isra.4 (wayland-client.c:1274)
    by 0x5493A13: dispatch_queue (wayland-client.c:1420)
    by 0x5493A13: wl_display_dispatch_queue_pending
(wayland-client.c:1662)
    by 0x5493D2E: wl_display_roundtrip_queue (wayland-client.c:1085)
    by 0x4232EC: xwl_screen_init (xwayland.c:632)
    by 0x439F50: AddScreen (dispatch.c:3864)

Split xwl_output_destroy() into xwl_output_destroy() which frees the
wl_output and the xwl_output structure, and xwl_output_remove() which
does the RRCrtcDestroy() and RROutputDestroy() and call the latter only
when an output is effectively removed.

An additional benefit, on top of avoiding a double free, is to avoid
updating the screen size at shutdown.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>