Re: [Intel-gfx] [PATCH] drm/atomic-helper: Fix leak in disable_all

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 17-07-17 om 17:21 schreef Daniel Vetter:
> On Mon, Jul 17, 2017 at 11:39:56AM +0200, Maarten Lankhorst wrote:
>> Op 15-07-17 om 11:31 schreef Daniel Vetter:
>>> The legacy plane->fb pointer is refcounted by calling
>>> drm_atomic_clean_old_fb().
>>>
>>> In practice this isn't a real problem because:
>>> - The caller in the i915 gpu reset code restores the original state
>>>   again, which means the plane->fb pointer won't change, hence can't
>>>   leak.
>>> - Drivers using drm_atomic_helper_shutdown call the fbdev cleanup
>>>   first, and that usually cleans up the fb through
>>>   drm_remove_framebuffer, which does this correctly.
>>> - Without fbdev the only framebuffers are from userspace, and those
>>>   get cleaned up (again using drm_remove_framebuffer) befor the driver
>>>   can even be unloaded.
>>>
>>> But in i915 I've switched the cleanup sequence around so that the
>>> _shutdown() calls happens after the drm_remove_framebuffer(), which is
>>> how I discovered this issue.
>>>
>>> v2: My analysis why the current code was ok for gpu reset and
>>> suspend/resume was correct, but then I totally failed to realize that
>>> we better keep this symmetric. Thanksfully CI noticed that for
>>> balance, a refcounting bug must exist at 2 places if previously there
>>> was no issue ...
>>>
>>> v3: Don't be lazy and compute the plane_mask in
>>> commit_duplicated_state properly too, instead of just using ~0U.
>>>
>>> Cc: martin.peres@free.fr
>>> Cc: chris@chris-wilson.co.uk
>>> Acked-by: Dave Airlie <airlied@gmail.com> (v1)
>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>> ---
>>>  drivers/gpu/drm/drm_atomic_helper.c | 18 ++++++++++++++++--
>>>  1 file changed, 16 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>>> index b07fc30372d3..545328a9a769 100644
>>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>>> @@ -2726,6 +2726,7 @@ int drm_atomic_helper_disable_all(struct drm_device *dev,
>>>  	struct drm_plane *plane;
>>>  	struct drm_crtc_state *crtc_state;
>>>  	struct drm_crtc *crtc;
>>> +	unsigned plane_mask = 0;
>>>  	int ret, i;
>>>  
>>>  	state = drm_atomic_state_alloc(dev);
>>> @@ -2768,10 +2769,14 @@ int drm_atomic_helper_disable_all(struct drm_device *dev,
>>>  			goto free;
>>>  
>>>  		drm_atomic_set_fb_for_plane(plane_state, NULL);
>>> +		plane_mask |= BIT(drm_plane_index(plane));
>>> +		plane->old_fb = plane->fb;
>>>  	}
>>>  
>>>  	ret = drm_atomic_commit(state);
>>>  free:
>>> +	if (plane_mask)
>>> +		drm_atomic_clean_old_fb(dev, plane_mask, ret);
>>>  	drm_atomic_state_put(state);
>>>  	return ret;
>>>  }
>>> @@ -2902,11 +2907,16 @@ int drm_atomic_helper_commit_duplicated_state(struct drm_atomic_state *state,
>>>  	struct drm_connector_state *new_conn_state;
>>>  	struct drm_crtc *crtc;
>>>  	struct drm_crtc_state *new_crtc_state;
>>> +	unsigned plane_mask = 0;
>>> +	struct drm_device *dev = state->dev;
>>> +	int ret;
>>>  
>>>  	state->acquire_ctx = ctx;
>>>  
>>> -	for_each_new_plane_in_state(state, plane, new_plane_state, i)
>>> +	for_each_new_plane_in_state(state, plane, new_plane_state, i) {
>>> +		plane_mask |= BIT(drm_plane_index(plane));
>> We should really add a drm_plane_mask/drm_connector_mask at some point, to complement drm_crtc_mask.
>>>  		state->planes[i].old_state = plane->state;
>>> +	}
>>>  
>>>  	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i)
>>>  		state->crtcs[i].old_state = crtc->state;
>>> @@ -2914,7 +2924,11 @@ int drm_atomic_helper_commit_duplicated_state(struct drm_atomic_state *state,
>>>  	for_each_new_connector_in_state(state, connector, new_conn_state, i)
>>>  		state->connectors[i].old_state = connector->state;
>>>  
>>> -	return drm_atomic_commit(state);
>>> +	ret = drm_atomic_commit(state);
>>> +	if (plane_mask)
>>> +		drm_atomic_clean_old_fb(dev, plane_mask, ret);
>> Kill the if () part, and make it unconditional? On second thought, I should have done the same in drm_framebuffer.c
> I'd prefer to not bikeshed this stuff too much and just go with what we do
> everywhere else (i.e. rmfb code and atomic commit) for consistency.
> clean_old_fb is definitely a horrible function with misleading kerneldoc
> on top, and I think the best way to clean that up would be to:
>
> - Move the plane_mask computation in drm_atmic_commit and also put the
>   clean_old_fb call in there. Maybe give it a more descriptive name like
>   update_legacy_fb or whatever. Unexport them.
>
> - This would break the compat helpers, where drm_atomic_commit must not
>   update the legacy refcounts, because for set_config, page_flip and the
>   plane hooks the core does that already. Create a
>   drm_atomic_commit_legacy for these.
>
> But since one of my patches caused an existing issue to pop up as a
> regression, and this series fixes it, I'd like to first get the minimal
> fix in through drm-intel. And then bikeshed it properly in drm-misc.
>
> Typing the patches is also a bit annoying right now since I have a few
> other atomic_commit patches in-flight ...
I'd prefer a bright gray bikeshed,

but hey..

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

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