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

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Mar 06, 2018 at 11:23:23AM -0500, Harry Wentland wrote:
> On 2018-03-06 07:18 AM, Ville Syrjälä wrote:
> > On Tue, Mar 06, 2018 at 10:31:27AM +0100, Daniel Vetter wrote:
> >> 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)?
> > 
> > It was some MST thing I believe... (should have written it down)
> > 
> > amdgpu_dm_atomic_check() -> dm_update_crtcs_state() ->
> > create_stream_for_sink() -> dm_dp_mst_dc_sink_create() ->
> > get_edid/update_edid_property
> > 
> 
> Yeah, it's because the dc_sink carries the EDID and is only created at
> this point for us. It's bugged me ever since we did this. Might be time
> to think of a solution to it now.

But how does this work? Userspace won't do a modeset without the EDID
present and the modes listed, which means you'll never ever end up in
atomic check. This really sounds rather wrong.

Only idea I can come up with is that you're abusing the regular pageflip
request as a worker thread, but that's some seriously backwards design.
-Daniel

> 
> Harry
> 
> >>
> >> 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
> > 

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