On Wed, May 18, 2016 at 04:37:36PM +0100, Jon Hunter wrote:
> Commit d2307dea14a4 ("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
> d2307dea14a4 ("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 d2307dea14a4
> ("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: d2307dea14a4 ("drm/atomic: use connector references (v3)")
>
> Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Acked-by: Thierry Reding <treding@xxxxxxxxxx>
Applied to drm-misc, thanks.
-Daniel
> ---
>
> V3 changes:
> - Dropped WARN_ON
>
> V2 changes:
> - Updated to next-20160518
> - Replaced open coding of call to drm_connector_reference() with
> __drm_atomic_helper_connector_duplicate_state() per Daniel's feedback.
>
> drivers/gpu/drm/tegra/dsi.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/tegra/dsi.c b/drivers/gpu/drm/tegra/dsi.c
> index 44e102799195..d1239ebc190f 100644
> --- a/drivers/gpu/drm/tegra/dsi.c
> +++ b/drivers/gpu/drm/tegra/dsi.c
> @@ -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,
> + ©->base);
> +
> return ©->base;
> }
>
> --
> 2.1.4
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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