Re: [RFC][PATCH 11/11] drm: Sprinkle lockdep asserts for edid/display_info

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Feb 27, 2018 at 02:57:00PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> edid and display_info are protected by mode_config.mutex. Add lockdep
> asserts to make sure we're not accessing things w/o the lock.
> 
> FIXME: pretty sure this will blow up with amdgpu as they seem
> to be doing edid updates even from the modeset path. Need to figure
> out what to do about that. Maybe protect the edid/display info with
> with connection_mutex instead of mode_config.mutex?

Imo not doing EDID udpates from the modeset path is the right fix. I can't
think of any reasonable reason to do that at least. Can you point me at
the relevant amdgpu code pls (I'm lazy, sry)?

Otherwise I think this is a real good patch.

Thanks, Daniel

> 
> Cc: Keith Packard <keithp@keithp.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c    | 4 ++++
>  drivers/gpu/drm/drm_edid.c         | 2 ++
>  drivers/gpu/drm/drm_probe_helper.c | 2 +-
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 122060792b6f..a9f3536f4e94 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1374,6 +1374,8 @@ int drm_mode_connector_update_edid_property(struct drm_connector *connector,
>  	size_t size = 0;
>  	int ret;
>  
> +	lockdep_assert_held(&dev->mode_config.mutex);
> +
>  	/* ignore requests to set edid when overridden */
>  	if (connector->override_edid)
>  		return 0;
> @@ -1770,6 +1772,8 @@ void drm_connector_reset_display_info(struct drm_connector *connector)
>  {
>  	struct drm_display_info *info = &connector->display_info;
>  
> +	lockdep_assert_held(&connector->dev->mode_config.mutex);
> +
>  	memset(info, 0, sizeof(*info));
>  }
>  EXPORT_SYMBOL_GPL(drm_connector_reset_display_info);
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 618093c4a039..7f9e9236114b 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -4440,6 +4440,8 @@ u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edi
>  	struct drm_display_info *info = &connector->display_info;
>  	u32 quirks = edid_get_quirks(edid);
>  
> +	lockdep_assert_held(&connector->dev->mode_config.mutex);
> +
>  	info->width_mm = edid->width_cm * 10;
>  	info->height_mm = edid->height_cm * 10;
>  
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 7dc7e635d7e4..2a2afcf72788 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -400,7 +400,7 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  	enum drm_connector_status old_status;
>  	struct drm_modeset_acquire_ctx ctx;
>  
> -	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
> +	lockdep_assert_held(&dev->mode_config.mutex);
>  
>  	drm_modeset_acquire_init(&ctx, 0);
>  
> -- 
> 2.13.6
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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