Re: [PATCH v8 3/3] drm/fence: add out-fences support

[Gustavo Padovan]

Hi Brian,

2016-11-11 Brian Starkey <brian.starkey@xxxxxxx>:

> Hi Gustavo,
> 
> On Fri, Nov 11, 2016 at 02:16:09PM +0900, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> > 
> > Support DRM out-fences by creating a sync_file with a fence for each CRTC
> > that sets the OUT_FENCE_PTR property.
> > 
> > We use the out_fence pointer received in the OUT_FENCE_PTR prop to send
> > the sync_file fd back to userspace.
> > 
> > The sync_file and fd are allocated/created before commit, but the
> > fd_install operation only happens after we know that commit succeed.
> > 
> > v2: Comment by Rob Clark:
> > 	- Squash commit that adds DRM_MODE_ATOMIC_OUT_FENCE flag here.
> > 
> >    Comment by Daniel Vetter:
> > 	- Add clean up code for out_fences
> > 
> > v3: Comments by Daniel Vetter:
> > 	- create DRM_MODE_ATOMIC_EVENT_MASK
> > 	- userspace should fill out_fences_ptr with the crtc_ids for which
> > 	it wants fences back.
> > 
> > v4: Create OUT_FENCE_PTR properties and remove old approach.
> > 
> > v5: Comments by Brian Starkey:
> > 	- Remove extra fence_get() in atomic_ioctl()
> > 	- Check ret before iterating on the crtc_state
> > 	- check ret before fd_install
> > 	- set fence_state to NULL at the beginning
> > 	- check fence_state->out_fence_ptr before put_user()
> > 	- change order of fput() and put_unused_fd() on failure
> > 
> >     - Add access_ok() check to the out_fence_ptr received
> >     - Rebase after fence -> dma_fence rename
> >     - Store out_fence_ptr in the drm_atomic_state
> >     - Split crtc_setup_out_fence()
> >     - return -1 as out_fence with TEST_ONLY flag
> > 
> > v6: Comments by Daniel Vetter
> > 	- Add prepare/unprepare_crtc_signaling()
> > 	- move struct drm_out_fence_state to drm_atomic.c
> > 	- mark get_crtc_fence() as static
> > 
> >    Comments by Brian Starkey
> > 	- proper set fence_ptr fence_state array
> > 	- isolate fence_idx increment
> > 
> >    - improve error handling
> > 
> > v7: Comments by Daniel Vetter
> > 	- remove prefix from internal functions
> > 	- make out_fence_ptr an s64 pointer
> > 	- degrade DRM_INFO to DRM_DEBUG_ATOMIC when put_user fail
> > 	- fix doc issues
> > 	- filter out OUT_FENCE_PTR == NULL and do fail in this case
> 
> Do *not* fail in this case?
> 
> > 	- add complete_crtc_signalling()
> > 	- krealloc fence_state on demand
> > 
> >    Comment by Brian Starkey
> > 	- remove unused crtc_state arg from get_out_fence()
> > 
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> 
> From an integration with writeback point of view, this looks fine to
> me - I can add writeback to this easily.
> 
> A few comments below though:
> 
> > ---
> > drivers/gpu/drm/drm_atomic.c | 242 +++++++++++++++++++++++++++++++++++--------
> > drivers/gpu/drm/drm_crtc.c   |   8 ++
> > include/drm/drm_atomic.h     |   1 +
> > include/drm/drm_crtc.h       |   6 ++
> > 4 files changed, 212 insertions(+), 45 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 8e26ad1..cd39f13 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -290,6 +290,23 @@ drm_atomic_get_crtc_state(struct drm_atomic_state *state,
> > }
> > EXPORT_SYMBOL(drm_atomic_get_crtc_state);
> > 
> > +static void set_out_fence_for_crtc(struct drm_atomic_state *state,
> > +				   struct drm_crtc *crtc, u64 __user *fence_ptr)
> > +{
> > +	state->crtcs[drm_crtc_index(crtc)].out_fence_ptr = fence_ptr;
> > +}
> > +
> > +static u64 __user * get_out_fence_for_crtc(struct drm_atomic_state *state,
> > +					   struct drm_crtc *crtc)
> > +{
> > +	u64 __user *fence_ptr;
> > +
> > +	fence_ptr = state->crtcs[drm_crtc_index(crtc)].out_fence_ptr;
> > +	state->crtcs[drm_crtc_index(crtc)].out_fence_ptr = NULL;
> > +
> > +	return fence_ptr;
> > +}
> > +
> 
> You missed a couple of s/u64/s64/ in the two functions above.
> 
> > /**
> >  * drm_atomic_set_mode_for_crtc - set mode for CRTC
> >  * @state: the CRTC whose incoming state to update
> > @@ -491,6 +508,16 @@ int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
> > 					&replaced);
> > 		state->color_mgmt_changed |= replaced;
> > 		return ret;
> > +	} else if (property == config->prop_out_fence_ptr) {
> > +		s64 __user *fence_ptr = u64_to_user_ptr(val);
> > +
> > +		if (!fence_ptr)
> > +			return 0;
> > +
> > +		if (!access_ok(VERIFY_WRITE, fence_ptr, sizeof(*fence_ptr)))
> > +			return -EFAULT;
> > +
> > +		set_out_fence_for_crtc(state->state, crtc, fence_ptr);
> > 	} else if (crtc->funcs->atomic_set_property)
> > 		return crtc->funcs->atomic_set_property(crtc, state, property, val);
> > 	else
> > @@ -533,6 +560,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
> > 		*val = (state->ctm) ? state->ctm->base.id : 0;
> > 	else if (property == config->gamma_lut_property)
> > 		*val = (state->gamma_lut) ? state->gamma_lut->base.id : 0;
> > +	else if (property == config->prop_out_fence_ptr)
> > +		*val = 0;
> > 	else if (crtc->funcs->atomic_get_property)
> > 		return crtc->funcs->atomic_get_property(crtc, state, property, val);
> > 	else
> > @@ -1659,11 +1688,9 @@ int drm_atomic_debugfs_init(struct drm_minor *minor)
> >  */
> > 
> > static struct drm_pending_vblank_event *create_vblank_event(
> > -		struct drm_device *dev, struct drm_file *file_priv,
> > -		struct dma_fence *fence, uint64_t user_data)
> > +		struct drm_device *dev, uint64_t user_data)
> > {
> > 	struct drm_pending_vblank_event *e = NULL;
> > -	int ret;
> > 
> > 	e = kzalloc(sizeof *e, GFP_KERNEL);
> > 	if (!e)
> > @@ -1673,17 +1700,6 @@ static struct drm_pending_vblank_event *create_vblank_event(
> > 	e->event.base.length = sizeof(e->event);
> > 	e->event.user_data = user_data;
> > 
> > -	if (file_priv) {
> > -		ret = drm_event_reserve_init(dev, file_priv, &e->base,
> > -					     &e->event.base);
> > -		if (ret) {
> > -			kfree(e);
> > -			return NULL;
> > -		}
> > -	}
> > -
> > -	e->base.fence = fence;
> > -
> > 	return e;
> > }
> > 
> > @@ -1788,6 +1804,166 @@ void drm_atomic_clean_old_fb(struct drm_device *dev,
> > }
> > EXPORT_SYMBOL(drm_atomic_clean_old_fb);
> > 
> > +static struct dma_fence *get_crtc_fence(struct drm_crtc *crtc)
> > +{
> > +	struct dma_fence *fence;
> > +
> > +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> > +	if (!fence)
> > +		return NULL;
> > +
> > +	dma_fence_init(fence, &drm_crtc_fence_ops, &crtc->fence_lock,
> > +		       crtc->fence_context, ++crtc->fence_seqno);
> > +
> > +	return fence;
> > +}
> > +
> > +struct drm_out_fence_state {
> > +	s64 __user *out_fence_ptr;
> > +	struct sync_file *sync_file;
> > +	int fd;
> > +};
> > +
> > +static int setup_out_fence(struct drm_out_fence_state *fence_state,
> > +			   struct dma_fence *fence)
> > +{
> > +	fence_state->fd = get_unused_fd_flags(O_CLOEXEC);
> > +	if (fence_state->fd < 0)
> > +		return fence_state->fd;
> > +
> > +	if (put_user(fence_state->fd, fence_state->out_fence_ptr))
> > +		return -EFAULT;
> > +
> > +	fence_state->sync_file = sync_file_create(fence);
> > +	if(!fence_state->sync_file)
> > +		return -ENOMEM;
> > +
> > +	return 0;
> > +}
> > +
> > +static int prepare_crtc_signaling(struct drm_device *dev,
> > +				  struct drm_atomic_state *state,
> > +				  struct drm_mode_atomic *arg,
> > +				  struct drm_file *file_priv,
> > +				  struct drm_out_fence_state **fence_state,
> > +				  unsigned int *num_fences)
> > +{
> > +	struct drm_crtc *crtc;
> > +	struct drm_crtc_state *crtc_state;
> > +	int i, ret;
> > +
> > +	for_each_crtc_in_state(state, crtc, crtc_state, i) {
> > +		u64 __user *fence_ptr;
> > +
> > +		fence_ptr = get_out_fence_for_crtc(crtc_state->state, crtc);
> > +
> > +		if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY && fence_ptr) {
> > +			if (put_user(-1, fence_ptr))
> > +				return -EFAULT;
> > +
> > +			continue;
> > +		}
> > +
> > +		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT || fence_ptr) {
> > +			struct drm_pending_vblank_event *e;
> > +
> > +			e = create_vblank_event(dev, arg->user_data);
> > +			if (!e)
> > +				return -ENOMEM;
> > +
> > +			crtc_state->event = e;
> > +		}
> > +
> > +		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> > +			struct drm_pending_vblank_event *e = crtc_state->event;
> > +
> > +			if (!file_priv)
> > +				continue;
> > +
> > +			ret = drm_event_reserve_init(dev, file_priv, &e->base,
> > +						     &e->event.base);
> > +			if (ret) {
> > +				kfree(e);
> > +				crtc_state->event = NULL;
> > +				return ret;
> > +			}
> > +		}
> > +
> > +		if (fence_ptr) {
> > +			struct dma_fence *fence;
> > +			struct drm_out_fence_state *f;
> > +
> > +			f = krealloc(*fence_state, sizeof(**fence_state) *
> > +				     (*num_fences + 1), GFP_KERNEL);
> > +			if (!f)
> > +				return -ENOMEM;
> > +
> > +			f[*num_fences].out_fence_ptr = fence_ptr;
> > +
> > +			fence = get_crtc_fence(crtc);
> > +			if (!fence)
> > +				return -ENOMEM;
> > +
> > +			ret = setup_out_fence(&f[*num_fences], fence);
> > +			if (ret) {
> > +				dma_fence_put(fence);
> > +				return ret;
> > +			}
> 
> Looks to me that the cleanup path doesn't work here. If
> setup_out_fence fails, you bail out before incrementing num_fences,
> and so the cleanup loop will be an iteration short.
> 
> > +
> > +			(*num_fences)++;
> > +
> > +			*fence_state = f;
> 
> I think this is problematic too. If I understand krealloc right, when
> you bail out before here and f != *fence_state, then the old
> *fence_state will have been already freed, and f is going to leak.

Yes, it is broken, I missed that. I think for fence_state I can just
move the assignment a few lines above and for num_fences one way is to
increment it before returning on error.

> 
> > +			crtc_state->event->base.fence = fence;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static void complete_crtc_signaling(struct drm_device *dev,
> > +				     struct drm_atomic_state *state,
> > +				     struct drm_out_fence_state *fence_state,
> > +				     unsigned int num_fences, int ret)
> > +{
> > +	struct drm_crtc *crtc;
> > +	struct drm_crtc_state *crtc_state;
> > +	int i;
> > +
> > +	if (!ret) {
> > +		for (i = 0; i < num_fences; i++)
> > +			fd_install(fence_state[i].fd,
> > +				   fence_state[i].sync_file->file);
> > +		return;
> > +	}
> > +
> > +	if (!fence_state)
> > +		return;
> > +
> > +	for_each_crtc_in_state(state, crtc, crtc_state, i) {
> > +		/*
> > +		 * TEST_ONLY and PAGE_FLIP_EVENT are mutually
> > +		 * exclusive, if they weren't, this code should be
> > +		 * called on success for TEST_ONLY too.
> > +		 */
> > +		if (crtc_state->event)
> > +			drm_event_cancel_free(dev, &crtc_state->event->base);
> > +	}
> 
> I think this event cleanup needs to be before the !fence_state check;
> userspace can ask for events but no fences, and if that fails then the
> events need to be freed.

Yes. In the previous version this was the correct flow, but with v8 the
clean up actually needs to happen before.

Gustavo