Quoting Christian König (2018-08-07 19:18:55)
Am 07.08.2018 um 20:14 schrieb Chris Wilson:
Quoting Christian König (2018-08-07 18:57:16)
Am 07.08.2018 um 18:08 schrieb Chris Wilson:
amdgpu only uses shared-fences internally, but dmabuf importers rely on implicit write hazard tracking via the reservation_object.fence_excl. For example, the importer use the write hazard for timing a page flip to only occur after the exporter has finished flushing its write into the surface. As such, on exporting a dmabuf, we must either flush all outstanding fences (for we do not know which are writes and should have been exclusive) or alternatively create a new exclusive fence that is the composite of all the existing shared fences, and so will only be signaled when all earlier fences are signaled (ensuring that we can not be signaled before the completion of any earlier write).
v2: reservation_object is already locked by amdgpu_bo_reserve()
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107341 Testcase: igt/amd_prime/amd-to-i915 References: 8e94a46c1770 ("drm/amdgpu: Attach exclusive fence to prime exported bo's. (v5)") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Alex Deucher alexander.deucher@amd.com Cc: "Christian König" christian.koenig@amd.com
This time, hopefully proofread and references complete. -Chris
drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c | 68 ++++++++++++++++++++--- 1 file changed, 60 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c index 1c5d97f4b4dd..dff2b01a3d89 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c @@ -37,6 +37,7 @@ #include "amdgpu_display.h" #include <drm/amdgpu_drm.h> #include <linux/dma-buf.h> +#include <linux/dma-fence-array.h>
static const struct dma_buf_ops amdgpu_dmabuf_ops;
@@ -188,6 +189,57 @@ amdgpu_gem_prime_import_sg_table(struct drm_device *dev, return ERR_PTR(ret); }
+static int +__reservation_object_make_exclusive(struct reservation_object *obj) +{
struct reservation_object_list *fobj;struct dma_fence_array *array;struct dma_fence **fences;unsigned int count, i;fobj = reservation_object_get_list(obj);if (!fobj)return 0;count = !!rcu_access_pointer(obj->fence_excl);count += fobj->shared_count;fences = kmalloc_array(count, sizeof(*fences), GFP_KERNEL);if (!fences)return -ENOMEM;for (i = 0; i < fobj->shared_count; i++) {struct dma_fence *f =rcu_dereference_protected(fobj->shared[i],reservation_object_held(obj));fences[i] = dma_fence_get(f);}if (rcu_access_pointer(obj->fence_excl)) {struct dma_fence *f =rcu_dereference_protected(obj->fence_excl,reservation_object_held(obj));fences[i] = dma_fence_get(f);}array = dma_fence_array_create(count, fences,dma_fence_context_alloc(1), 0,false);if (!array)goto err_fences_put;reservation_object_add_excl_fence(obj, &array->base);return 0;+err_fences_put:
for (i = 0; i < count; i++)dma_fence_put(fences[i]);kfree(fences);return -ENOMEM;+}
This can be simplified a lot. See amdgpu_pasid_free_delayed() for an example:
{ if (!reservation_object_get_list(obj)) return 0;
r = reservation_object_get_fences_rcu(obj, NULL, &count, &fences); if (r) return r; array = dma_fence_array_create(count, fences, dma_fence_context_alloc(1), 0, false); if (!array) goto err_fences_put; reservation_object_add_excl_fence(obj, &array->base); return 0;err: ... }
My starting point was going to be use get_fences_rcu, but get_fences_rcu can hardly be called simple for where the lock is required to be held start to finish ;)
What are you talking about? get_fences_rcu doesn't require any locking at all.
You only need to the locking to make sure that between creating the fence array and calling reservation_object_add_excl_fence() no other fence is added.
Exactly. That's what need to be absolutely clear from the context. I didn't say anything about the locking requirements for get_fences_rcu just the opposite. -Chris