[PATCH v3] drm/syncobj: use newly allocated stub fences

[David Stevens]

Pushing to drm-misc-next works for me. Thanks for the quick responses.

-David

On Thu, Apr 8, 2021 at 6:56 PM Christian König <christian.koenig at amd.com> wrote:
>
> Am 08.04.21 um 11:54 schrieb David Stevens:
> > From: David Stevens <stevensd at chromium.org>
> >
> > Allocate a new private stub fence in drm_syncobj_assign_null_handle,
> > instead of using a static stub fence.
> >
> > When userspace creates a fence with DRM_SYNCOBJ_CREATE_SIGNALED or when
> > userspace signals a fence via DRM_IOCTL_SYNCOBJ_SIGNAL, the timestamp
> > obtained when the fence is exported and queried with SYNC_IOC_FILE_INFO
> > should match when the fence's status was changed from the perspective of
> > userspace, which is during the respective ioctl.
> >
> > When a static stub fence started being used in by these ioctls, this
> > behavior changed. Instead, the timestamp returned by SYNC_IOC_FILE_INFO
> > became the first time anything used the static stub fence, which has no
> > meaning to userspace.
> >
> > Signed-off-by: David Stevens <stevensd at chromium.org>
>
> Reviewed-by: Christian König <christian.koenig at amd.com>
>
> Should I push this to drm-misc-next or how do you want to upstream it?
>
> Thanks,
> Christian.
>
> > ---
> > v2 -> v3:
> >   - reuse the static stub spinlock
> > v1 -> v2:
> >   - checkpatch style fixes
> >
> >   drivers/dma-buf/dma-fence.c   | 27 ++++++++++++++++++++++++++-
> >   drivers/gpu/drm/drm_syncobj.c | 25 +++++++++++++++++++------
> >   include/linux/dma-fence.h     |  1 +
> >   3 files changed, 46 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> > index d64fc03929be..ce0f5eff575d 100644
> > --- a/drivers/dma-buf/dma-fence.c
> > +++ b/drivers/dma-buf/dma-fence.c
> > @@ -123,7 +123,9 @@ static const struct dma_fence_ops dma_fence_stub_ops = {
> >   /**
> >    * dma_fence_get_stub - return a signaled fence
> >    *
> > - * Return a stub fence which is already signaled.
> > + * Return a stub fence which is already signaled. The fence's
> > + * timestamp corresponds to the first time after boot this
> > + * function is called.
> >    */
> >   struct dma_fence *dma_fence_get_stub(void)
> >   {
> > @@ -141,6 +143,29 @@ struct dma_fence *dma_fence_get_stub(void)
> >   }
> >   EXPORT_SYMBOL(dma_fence_get_stub);
> >
> > +/**
> > + * dma_fence_allocate_private_stub - return a private, signaled fence
> > + *
> > + * Return a newly allocated and signaled stub fence.
> > + */
> > +struct dma_fence *dma_fence_allocate_private_stub(void)
> > +{
> > +     struct dma_fence *fence;
> > +
> > +     fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> > +     if (fence == NULL)
> > +             return ERR_PTR(-ENOMEM);
> > +
> > +     dma_fence_init(fence,
> > +                    &dma_fence_stub_ops,
> > +                    &dma_fence_stub_lock,
> > +                    0, 0);
> > +     dma_fence_signal(fence);
> > +
> > +     return fence;
> > +}
> > +EXPORT_SYMBOL(dma_fence_allocate_private_stub);
> > +
> >   /**
> >    * dma_fence_context_alloc - allocate an array of fence contexts
> >    * @num: amount of contexts to allocate
> > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> > index 349146049849..a54aa850d143 100644
> > --- a/drivers/gpu/drm/drm_syncobj.c
> > +++ b/drivers/gpu/drm/drm_syncobj.c
> > @@ -350,12 +350,16 @@ EXPORT_SYMBOL(drm_syncobj_replace_fence);
> >    *
> >    * Assign a already signaled stub fence to the sync object.
> >    */
> > -static void drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
> > +static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
> >   {
> > -     struct dma_fence *fence = dma_fence_get_stub();
> > +     struct dma_fence *fence = dma_fence_allocate_private_stub();
> > +
> > +     if (IS_ERR(fence))
> > +             return PTR_ERR(fence);
> >
> >       drm_syncobj_replace_fence(syncobj, fence);
> >       dma_fence_put(fence);
> > +     return 0;
> >   }
> >
> >   /* 5s default for wait submission */
> > @@ -469,6 +473,7 @@ EXPORT_SYMBOL(drm_syncobj_free);
> >   int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
> >                      struct dma_fence *fence)
> >   {
> > +     int ret;
> >       struct drm_syncobj *syncobj;
> >
> >       syncobj = kzalloc(sizeof(struct drm_syncobj), GFP_KERNEL);
> > @@ -479,8 +484,13 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
> >       INIT_LIST_HEAD(&syncobj->cb_list);
> >       spin_lock_init(&syncobj->lock);
> >
> > -     if (flags & DRM_SYNCOBJ_CREATE_SIGNALED)
> > -             drm_syncobj_assign_null_handle(syncobj);
> > +     if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
> > +             ret = drm_syncobj_assign_null_handle(syncobj);
> > +             if (ret < 0) {
> > +                     drm_syncobj_put(syncobj);
> > +                     return ret;
> > +             }
> > +     }
> >
> >       if (fence)
> >               drm_syncobj_replace_fence(syncobj, fence);
> > @@ -1322,8 +1332,11 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
> >       if (ret < 0)
> >               return ret;
> >
> > -     for (i = 0; i < args->count_handles; i++)
> > -             drm_syncobj_assign_null_handle(syncobjs[i]);
> > +     for (i = 0; i < args->count_handles; i++) {
> > +             ret = drm_syncobj_assign_null_handle(syncobjs[i]);
> > +             if (ret < 0)
> > +                     break;
> > +     }
> >
> >       drm_syncobj_array_free(syncobjs, args->count_handles);
> >
> > diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> > index 9f12efaaa93a..6ffb4b2c6371 100644
> > --- a/include/linux/dma-fence.h
> > +++ b/include/linux/dma-fence.h
> > @@ -587,6 +587,7 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
> >   }
> >
> >   struct dma_fence *dma_fence_get_stub(void);
> > +struct dma_fence *dma_fence_allocate_private_stub(void);
> >   u64 dma_fence_context_alloc(unsigned num);
> >
> >   #define DMA_FENCE_TRACE(f, fmt, args...) \
>