Commit 280dc0e1 authored May 18, 2016 by Jon Hunter Committed by Daniel Vetter May 18, 2016

drm/tegra: Fix crash caused by reference count imbalance



Commit d2307dea ("drm/atomic: use connector references (v3)") added
reference counting for DRM connectors and this caused a crash when
exercising system suspend on Tegra114 Dalmore.

The Tegra DSI driver implements a Tegra specific function,
tegra_dsi_connector_duplicate_state(), to duplicate the connector state
and destroys the state using the generic helper function,
drm_atomic_helper_connector_destroy_state(). Following commit
d2307dea ("drm/atomic: use connector references (v3)") there is
now an imbalance in the connector reference count because the Tegra
function to duplicate state does not take a reference when duplicating
the state information. However, the generic helper function to destroy
the state information assumes a reference has been taken and during
system suspend, when the connector state is destroyed, this leads to a
crash because we attempt to put the reference for an object that has
already been freed.

Fix this by calling __drm_atomic_helper_connector_duplicate_state() from
tegra_dsi_connector_duplicate_state() to ensure that we take a reference
on a connector if crtc is set. Note that this will also copy the
connector state a 2nd time, but this should be harmless.

By fixing tegra_dsi_connector_duplicate_state() to take a reference,
although a crash was no longer seen, it was then observed that after
each system suspend-resume cycle, the reference would be one greater
than before the suspend-resume cycle. Following commit d2307dea
("drm/atomic: use connector references (v3)"), it was found that we
also need to put the reference when calling the function
tegra_dsi_connector_reset() before freeing the state. Fix this by
updating tegra_dsi_connector_reset() to call the function
__drm_atomic_helper_connector_destroy_state() in order to put the
reference for the connector.

Fixes: d2307dea ("drm/atomic: use connector references (v3)")

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1463585856-16606-1-git-send-email-jonathanh@nvidia.com

parent fdf2c85f

drivers/gpu/drm/tegra/dsi.c

+11 −4

Original line number	Diff line number	Diff line
		@@ -745,13 +745,17 @@ static void tegra_dsi_soft_reset(struct tegra_dsi *dsi)

		static void tegra_dsi_connector_reset(struct drm_connector *connector)
		{
		struct tegra_dsi_state *state =
		kzalloc(sizeof(*state), GFP_KERNEL);
		struct tegra_dsi_state state = kzalloc(sizeof(state), GFP_KERNEL);

		if (state) {
		if (!state)
		return;

		if (connector->state) {
		__drm_atomic_helper_connector_destroy_state(connector->state);
		kfree(connector->state);
		__drm_atomic_helper_connector_reset(connector, &state->base);
		}

		__drm_atomic_helper_connector_reset(connector, &state->base);
		}

		static struct drm_connector_state *
		@@ -764,6 +768,9 @@ tegra_dsi_connector_duplicate_state(struct drm_connector *connector)
		if (!copy)
		return NULL;

		__drm_atomic_helper_connector_duplicate_state(connector,
		&copy->base);

		return &copy->base;
		}