Re: [PATCH 4/7] dma-buf: rename and cleanup dma_resv_get_excl

[Jason Ekstrand <jason@jlekstrand.net>]

On Wed, Jun 2, 2021 at 7:43 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Wed, Jun 02, 2021 at 01:17:11PM +0200, Christian König wrote:
> > When the comment needs to state explicitly that this
> > doesn't get a reference to the object then the function
> > is named rather badly.
> >
> > Rename the function and use rcu_dereference_check(), this
> > way it can be used from both rcu as well as lock protected
> > critical sections.
> >
> > Signed-off-by: Christian König <christian.koenig@amd.com>
>
> I'd call this dma_resv_exlusive_fence, since without that it's a bit close

Or, if we want to keep it shorter, dma_resv_excl_fence().  I don't
care much either way

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

> to dma_resv_make_exclusive or something like that. But this is definitely
> better than the previous pointer deref in a "I'm totally getting you a
> full reference" trenchcoat thing.
>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>
> > ---
> >  drivers/dma-buf/dma-buf.c                |  4 ++--
> >  drivers/dma-buf/dma-resv.c               | 10 +++++-----
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c  |  2 +-
> >  drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c |  2 +-
> >  drivers/gpu/drm/etnaviv/etnaviv_gem.c    |  2 +-
> >  drivers/gpu/drm/i915/gem/i915_gem_busy.c |  3 +--
> >  drivers/gpu/drm/msm/msm_gem.c            |  4 ++--
> >  drivers/gpu/drm/nouveau/nouveau_bo.c     |  2 +-
> >  drivers/gpu/drm/nouveau/nouveau_fence.c  |  2 +-
> >  drivers/gpu/drm/radeon/radeon_display.c  |  2 +-
> >  drivers/gpu/drm/radeon/radeon_sync.c     |  2 +-
> >  drivers/gpu/drm/radeon/radeon_uvd.c      |  2 +-
> >  drivers/gpu/drm/ttm/ttm_bo.c             |  2 +-
> >  drivers/gpu/drm/vmwgfx/vmwgfx_resource.c |  2 +-
> >  include/linux/dma-resv.h                 | 13 +++++--------
> >  15 files changed, 25 insertions(+), 29 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index d3b4e370dbc1..4d0ddc712f1e 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -234,7 +234,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
> >               shared_count = fobj->shared_count;
> >       else
> >               shared_count = 0;
> > -     fence_excl = rcu_dereference(resv->fence_excl);
> > +     fence_excl = dma_resv_exclusive(resv);
> >       if (read_seqcount_retry(&resv->seq, seq)) {
> >               rcu_read_unlock();
> >               goto retry;
> > @@ -1385,7 +1385,7 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
> >               robj = buf_obj->resv;
> >               seq = read_seqcount_begin(&robj->seq);
> >               rcu_read_lock();
> > -             fence = rcu_dereference(robj->fence_excl);
> > +             fence = dma_resv_exclusive(robj);
> >               if (fence)
> >                       seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
> >                                  fence->ops->get_driver_name(fence),
> > diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> > index 6c6195315e9f..81b032b43457 100644
> > --- a/drivers/dma-buf/dma-resv.c
> > +++ b/drivers/dma-buf/dma-resv.c
> > @@ -281,7 +281,7 @@ EXPORT_SYMBOL(dma_resv_add_shared_fence);
> >   */
> >  void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
> >  {
> > -     struct dma_fence *old_fence = dma_resv_get_excl(obj);
> > +     struct dma_fence *old_fence = dma_resv_exclusive(obj);
> >       struct dma_resv_list *old;
> >       u32 i = 0;
> >
> > @@ -377,7 +377,7 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src)
> >       rcu_read_unlock();
> >
> >       src_list = dma_resv_get_list(dst);
> > -     old = dma_resv_get_excl(dst);
> > +     old = dma_resv_exclusive(dst);
> >
> >       write_seqcount_begin(&dst->seq);
> >       /* write_seqcount_begin provides the necessary memory barrier */
> > @@ -425,7 +425,7 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
> >               rcu_read_lock();
> >               seq = read_seqcount_begin(&obj->seq);
> >
> > -             fence_excl = rcu_dereference(obj->fence_excl);
> > +             fence_excl = dma_resv_exclusive(obj);
> >               if (fence_excl && !dma_fence_get_rcu(fence_excl))
> >                       goto unlock;
> >
> > @@ -520,7 +520,7 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj,
> >       rcu_read_lock();
> >       i = -1;
> >
> > -     fence = rcu_dereference(obj->fence_excl);
> > +     fence = dma_resv_exclusive(obj);
> >       if (fence && !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> >               if (!dma_fence_get_rcu(fence))
> >                       goto unlock_retry;
> > @@ -642,7 +642,7 @@ bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all)
> >       }
> >
> >       if (!shared_count) {
> > -             struct dma_fence *fence_excl = rcu_dereference(obj->fence_excl);
> > +             struct dma_fence *fence_excl = dma_resv_exclusive(obj);
> >
> >               if (fence_excl) {
> >                       ret = dma_resv_test_signaled_single(fence_excl);
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > index 73c76a3e2b12..cd5146fa6fb6 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > @@ -226,7 +226,7 @@ static void amdgpu_gem_object_close(struct drm_gem_object *obj,
> >       if (!amdgpu_vm_ready(vm))
> >               goto out_unlock;
> >
> > -     fence = dma_resv_get_excl(bo->tbo.base.resv);
> > +     fence = dma_resv_exclusive(bo->tbo.base.resv);
> >       if (fence) {
> >               amdgpu_bo_fence(bo, fence, true);
> >               fence = NULL;
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > index 4e558632a5d2..c84d5b843985 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sync.c
> > @@ -210,7 +210,7 @@ int amdgpu_sync_resv(struct amdgpu_device *adev, struct amdgpu_sync *sync,
> >               return -EINVAL;
> >
> >       /* always sync to the exclusive fence */
> > -     f = dma_resv_get_excl(resv);
> > +     f = dma_resv_exclusive(resv);
> >       r = amdgpu_sync_fence(sync, f);
> >
> >       flist = dma_resv_get_list(resv);
> > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > index db69f19ab5bc..d4f54dea8ac1 100644
> > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > @@ -471,7 +471,7 @@ static void etnaviv_gem_describe(struct drm_gem_object *obj, struct seq_file *m)
> >               }
> >       }
> >
> > -     fence = rcu_dereference(robj->fence_excl);
> > +     fence = dma_resv_exclusive(robj);
> >       if (fence)
> >               etnaviv_gem_describe_fence(fence, "Exclusive", m);
> >       rcu_read_unlock();
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_busy.c b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> > index 25235ef630c1..02312a0c3a36 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> > @@ -113,8 +113,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
> >       seq = raw_read_seqcount(&obj->base.resv->seq);
> >
> >       /* Translate the exclusive fence to the READ *and* WRITE engine */
> > -     args->busy =
> > -             busy_check_writer(rcu_dereference(obj->base.resv->fence_excl));
> > +     args->busy = busy_check_writer(dma_resv_exclusive(obj->base.resv));
> >
> >       /* Translate shared fences to READ set of engines */
> >       list = rcu_dereference(obj->base.resv->fence);
> > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> > index 56df86e5f740..54c1b53426d6 100644
> > --- a/drivers/gpu/drm/msm/msm_gem.c
> > +++ b/drivers/gpu/drm/msm/msm_gem.c
> > @@ -819,7 +819,7 @@ int msm_gem_sync_object(struct drm_gem_object *obj,
> >
> >       fobj = dma_resv_get_list(obj->resv);
> >       if (!fobj || (fobj->shared_count == 0)) {
> > -             fence = dma_resv_get_excl(obj->resv);
> > +             fence = dma_resv_exclusive(obj->resv);
> >               /* don't need to wait on our own fences, since ring is fifo */
> >               if (fence && (fence->context != fctx->context)) {
> >                       ret = dma_fence_wait(fence, true);
> > @@ -1035,7 +1035,7 @@ void msm_gem_describe(struct drm_gem_object *obj, struct seq_file *m,
> >               }
> >       }
> >
> > -     fence = rcu_dereference(robj->fence_excl);
> > +     fence = dma_resv_exclusive(robj);
> >       if (fence)
> >               describe_fence(fence, "Exclusive", m);
> >       rcu_read_unlock();
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > index e688ca77483d..ac0ebcc4ebb7 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > @@ -955,7 +955,7 @@ nouveau_bo_vm_cleanup(struct ttm_buffer_object *bo,
> >  {
> >       struct nouveau_drm *drm = nouveau_bdev(bo->bdev);
> >       struct drm_device *dev = drm->dev;
> > -     struct dma_fence *fence = dma_resv_get_excl(bo->base.resv);
> > +     struct dma_fence *fence = dma_resv_exclusive(bo->base.resv);
> >
> >       nv10_bo_put_tile_region(dev, *old_tile, fence);
> >       *old_tile = new_tile;
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > index e5dcbf67de7e..a6cb35181aee 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > @@ -356,7 +356,7 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan, bool e
> >       }
> >
> >       fobj = dma_resv_get_list(resv);
> > -     fence = dma_resv_get_excl(resv);
> > +     fence = dma_resv_exclusive(resv);
> >
> >       if (fence && (!exclusive || !fobj || !fobj->shared_count)) {
> >               struct nouveau_channel *prev = NULL;
> > diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
> > index 652af7a134bd..57c910e5ae77 100644
> > --- a/drivers/gpu/drm/radeon/radeon_display.c
> > +++ b/drivers/gpu/drm/radeon/radeon_display.c
> > @@ -533,7 +533,7 @@ static int radeon_crtc_page_flip_target(struct drm_crtc *crtc,
> >               DRM_ERROR("failed to pin new rbo buffer before flip\n");
> >               goto cleanup;
> >       }
> > -     work->fence = dma_fence_get(dma_resv_get_excl(new_rbo->tbo.base.resv));
> > +     work->fence = dma_fence_get(dma_resv_exclusive(new_rbo->tbo.base.resv));
> >       radeon_bo_get_tiling_flags(new_rbo, &tiling_flags, NULL);
> >       radeon_bo_unreserve(new_rbo);
> >
> > diff --git a/drivers/gpu/drm/radeon/radeon_sync.c b/drivers/gpu/drm/radeon/radeon_sync.c
> > index 5d3302945076..e476f90ef1c1 100644
> > --- a/drivers/gpu/drm/radeon/radeon_sync.c
> > +++ b/drivers/gpu/drm/radeon/radeon_sync.c
> > @@ -98,7 +98,7 @@ int radeon_sync_resv(struct radeon_device *rdev,
> >       int r = 0;
> >
> >       /* always sync to the exclusive fence */
> > -     f = dma_resv_get_excl(resv);
> > +     f = dma_resv_exclusive(resv);
> >       fence = f ? to_radeon_fence(f) : NULL;
> >       if (fence && fence->rdev == rdev)
> >               radeon_sync_fence(sync, fence);
> > diff --git a/drivers/gpu/drm/radeon/radeon_uvd.c b/drivers/gpu/drm/radeon/radeon_uvd.c
> > index dfa9fdbe98da..02d4bbdc9111 100644
> > --- a/drivers/gpu/drm/radeon/radeon_uvd.c
> > +++ b/drivers/gpu/drm/radeon/radeon_uvd.c
> > @@ -477,7 +477,7 @@ static int radeon_uvd_cs_msg(struct radeon_cs_parser *p, struct radeon_bo *bo,
> >               return -EINVAL;
> >       }
> >
> > -     f = dma_resv_get_excl(bo->tbo.base.resv);
> > +     f = dma_resv_exclusive(bo->tbo.base.resv);
> >       if (f) {
> >               r = radeon_fence_wait((struct radeon_fence *)f, false);
> >               if (r) {
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index 5a7ab4b35b2d..92361556bf0b 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -262,7 +262,7 @@ static void ttm_bo_flush_all_fences(struct ttm_buffer_object *bo)
> >
> >       rcu_read_lock();
> >       fobj = rcu_dereference(resv->fence);
> > -     fence = rcu_dereference(resv->fence_excl);
> > +     fence = dma_resv_exclusive(resv);
> >       if (fence && !fence->ops->signaled)
> >               dma_fence_enable_sw_signaling(fence);
> >
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c b/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> > index 62ea920addc3..c78f38ee1c20 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> > @@ -1166,7 +1166,7 @@ int vmw_resources_clean(struct vmw_buffer_object *vbo, pgoff_t start,
> >               if (bo->moving)
> >                       dma_fence_put(bo->moving);
> >               bo->moving = dma_fence_get
> > -                     (dma_resv_get_excl(bo->base.resv));
> > +                     (dma_resv_exclusive(bo->base.resv));
> >       }
> >
> >       return 0;
> > diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> > index f32a3d176513..7549ec5eb35c 100644
> > --- a/include/linux/dma-resv.h
> > +++ b/include/linux/dma-resv.h
> > @@ -226,22 +226,19 @@ static inline void dma_resv_unlock(struct dma_resv *obj)
> >  }
> >
> >  /**
> > - * dma_resv_get_excl - get the reservation object's
> > - * exclusive fence, with update-side lock held
> > + * dma_resv_exclusive - return the object's exclusive fence
> >   * @obj: the reservation object
> >   *
> > - * Returns the exclusive fence (if any).  Does NOT take a
> > - * reference. Writers must hold obj->lock, readers may only
> > - * hold a RCU read side lock.
> > + * Returns the exclusive fence (if any). Caller must either hold the objects
> > + * lock or the rcu read side lock.
> >   *
> >   * RETURNS
> >   * The exclusive fence or NULL
> >   */
> >  static inline struct dma_fence *
> > -dma_resv_get_excl(struct dma_resv *obj)
> > +dma_resv_exclusive(struct dma_resv *obj)
> >  {
> > -     return rcu_dereference_protected(obj->fence_excl,
> > -                                      dma_resv_held(obj));
> > +     return rcu_dereference_check(obj->fence_excl, dma_resv_held(obj));
> >  }
> >
> >  /**
> > --
> > 2.25.1
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch