On Thu, May 12, 2016 at 10:57:01AM -0400, Lyude wrote:
> Unfortunately since we don't have Dave's connector refcounting patch
> here yet, it's very possible that drm_atomic_state_default_clear() could
> get called by intel_display_resume() when
> intel_dp_mst_destroy_connector() isn't completely finished destroying an
> mst connector, but has already finished setting connector->funcs to
> NULL. As such, we need to treat the connector like it's already been
> destroyed and just skip it, otherwise we'll end up dereferencing a NULL
> pointer.
>
> This fix is only required for 4.6 and below. David Airlie's patchseries
> for 4.7 to add connector reference counting provides a more proper fix
> for this.
>
> Upstream fix: b164d31f50b2923a7a92c2a40cb46973a6ba8c36
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
Not fixing the race at all, bug if it helps a few users in real-world
cases while the real bugfix trickles down into shipping kernels (it'll be
in 4.7 but just way too big for backporting) I'm ok with this.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> (but for stable
kernels only)
> ---
> drivers/gpu/drm/drm_atomic.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 8ee1db8..d3a5b5c 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -139,7 +139,7 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> for (i = 0; i < state->num_connector; i++) {
> struct drm_connector *connector = state->connectors[i];
>
> - if (!connector)
> + if (!connector || !connector->funcs)
> continue;
>
> /*
> @@ -150,6 +150,7 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
> * case by setting all connector pointers to NULL.
> */
> state->connector_states[i]->connector = NULL;
> +
> connector->funcs->atomic_destroy_state(NULL,
> state->connector_states[i]);
> state->connectors[i] = NULL;
> --
> 2.5.5
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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