text_backend: make destructor call explicit

Graphics / Wayland / Weston - Pekka Paalanen [collabora.co.uk] - 26 June 2015 01:33 UTC

We used to rely on the order in which the weston_compositor::destroy_signal callbacks happened, to not access freed memory. Don't know when, but this broke at least with ivi-shell, which caused crashes in random places on compositor shutdown.

Valgrind found the following:

Invalid write of size 8 at 0xC2EDC69: unbind_input_panel (input-panel-ivi.c:340) by 0x4E3B6BB: destroy_resource (wayland-server.c:537) by 0x4E3E085: for_each_helper.isra.0 (wayland-util.c:359) by 0x4E3E60D: wl_map_for_each (wayland-util.c:365) by 0x4E3BEC7: wl_client_destroy (wayland-server.c:675) by 0x4182F2: text_backend_notifier_destroy (text-backend.c:1047) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465) Address 0x67ea360 is 208 bytes inside a block of size 232 free'd at 0x4C2A6BC: free (vg_replace_malloc.c:473) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465)

Invalid write of size 8 at 0x4E3E0D7: wl_list_remove (wayland-util.c:57) by 0xC2EDEE9: destroy_input_panel_surface (input-panel-ivi.c:191) by 0x4E3B6BB: destroy_resource (wayland-server.c:537) by 0x4E3BC7B: wl_resource_destroy (wayland-server.c:550) by 0x40DB8B: wl_signal_emit (wayland-server-core.h:264) by 0x40DB8B: weston_surface_destroy (compositor.c:1883) by 0x40DB8B: weston_surface_destroy (compositor.c:1873) by 0x4E3B6BB: destroy_resource (wayland-server.c:537) by 0x4E3E085: for_each_helper.isra.0 (wayland-util.c:359) by 0x4E3E60D: wl_map_for_each (wayland-util.c:365) by 0x4E3BEC7: wl_client_destroy (wayland-server.c:675) by 0x4182F2: text_backend_notifier_destroy (text-backend.c:1047) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465) Address 0x67ea370 is 224 bytes inside a block of size 232 free'd at 0x4C2A6BC: free (vg_replace_malloc.c:473) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465)

Invalid write of size 8 at 0x4E3E0E7: wl_list_remove (wayland-util.c:58) by 0xC2EDEE9: destroy_input_panel_surface (input-panel-ivi.c:191) by 0x4E3B6BB: destroy_resource (wayland-server.c:537) by 0x4E3BC7B: wl_resource_destroy (wayland-server.c:550) by 0x40DB8B: wl_signal_emit (wayland-server-core.h:264) by 0x40DB8B: weston_surface_destroy (compositor.c:1883) by 0x40DB8B: weston_surface_destroy (compositor.c:1873) by 0x4E3B6BB: destroy_resource (wayland-server.c:537) by 0x4E3E085: for_each_helper.isra.0 (wayland-util.c:359) by 0x4E3E60D: wl_map_for_each (wayland-util.c:365) by 0x4E3BEC7: wl_client_destroy (wayland-server.c:675) by 0x4182F2: text_backend_notifier_destroy (text-backend.c:1047) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465) Address 0x67ea368 is 216 bytes inside a block of size 232 free'd at 0x4C2A6BC: free (vg_replace_malloc.c:473) by 0x4084FB: wl_signal_emit (wayland-server-core.h:264) by 0x4084FB: main (compositor.c:5465)

Looking at the first of these, unbind_input_panel() gets called when the text-backend destroys its helper client which has bound to input_panel interface. This happens after the shell's destroy_signal callback has been called, so the shell has already been freed.

The other two errors come from wl_list_remove(&input_panel_surface->link); which has gone stale when the shell was destroyed (shell->input_panel.surfaces list).

Rather than creating even more destroy listeners and hooking them up in spaghetti, modify text-backend to not hook up to the compositor destroy signal. Instead, make it the text_backend_init() callers' responsibility to also call text_backend_destroy() appropriately, before the shell goes away.

This fixed all the above Valgrind errors, and avoid a crash with ivi-shell when exiting Weston.

Also using desktop-shell exhibited similar Valgrind errors which are fixed by this patch, but those didn't happen to cause any crashes AFAIK.

aa9536a text_backend: make destructor call explicit
desktop-shell/shell.c | 4 +++-
desktop-shell/shell.h | 2 ++
ivi-shell/ivi-shell.c | 4 +++-
ivi-shell/ivi-shell.h | 2 ++
src/compositor.h | 7 ++++++-
src/text-backend.c | 18 +++++-------------
6 files changed, 21 insertions(+), 16 deletions(-)

Upstream: cgit.freedesktop.org

  • Share