[Intel-gfx] [PATCH 1/6] drm/atomic: Ensure that drm_connector_index is stable

[Rob Clark]

On Wed, Nov 19, 2014 at 12:38 PM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> I've totally forgotten that with DP MST connectors can now be
> hotplugged. And failed to adapt Rob's drm_atomic_state code (which
> predates connector hotplugging) to the new realities.
>
> The first step is to make sure that the connector indices used to
> access the arrays of pointers are stable. The connection mutex gives
> us enough guarantees for that, which means we won't unecessarily block
> on concurrent modesets or background probing.
>
> So add a locking WARN_ON and shuffle the code slightly to make sure we
> always hold the right lock.
>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>

Reviewed-by: Rob Clark <robdclark at gmail.com>

> ---
>  drivers/gpu/drm/drm_atomic.c | 8 ++++----
>  drivers/gpu/drm/drm_crtc.c   | 5 +++++
>  2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index ed22a719440f..90b2d1644bd7 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -295,15 +295,15 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state,
>         struct drm_mode_config *config = &connector->dev->mode_config;
>         struct drm_connector_state *connector_state;
>
> +       ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx);
> +       if (ret)
> +               return ERR_PTR(ret);
> +
>         index = drm_connector_index(connector);
>
>         if (state->connector_states[index])
>                 return state->connector_states[index];
>
> -       ret = drm_modeset_lock(&config->connection_mutex, state->acquire_ctx);
> -       if (ret)
> -               return ERR_PTR(ret);
> -
>         connector_state = connector->funcs->atomic_duplicate_state(connector);
>         if (!connector_state)
>                 return ERR_PTR(-ENOMEM);
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 56737e74b59d..5c878f172365 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -867,6 +867,8 @@ int drm_connector_init(struct drm_device *dev,
>
>         drm_connector_get_cmdline_mode(connector);
>
> +       /* We should add connectors at the end to avoid upsetting the connector
> +        * index too much. */
>         list_add_tail(&connector->head, &dev->mode_config.connector_list);
>         dev->mode_config.num_connector++;
>
> @@ -930,6 +932,9 @@ unsigned int drm_connector_index(struct drm_connector *connector)
>  {
>         unsigned int index = 0;
>         struct drm_connector *tmp;
> +       struct drm_mode_config *config = &connector->dev->mode_config;
> +
> +       WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
>
>         list_for_each_entry(tmp, &connector->dev->mode_config.connector_list, head) {
>                 if (tmp == connector)
> --
> 2.1.1
>
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