[PATCH 1/3] drm/radeon: use RCU query for GEM_BUSY syscall

[Grigori Goronzy]

We don't need to call the (expensive) radeon_bo_wait, checking the
fences via RCU is much faster. The reservation done by radeon_bo_wait
does not save us from any race conditions.
---
 drivers/gpu/drm/radeon/radeon_gem.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_gem.c 
b/drivers/gpu/drm/radeon/radeon_gem.c
index ac3c131..7199e19 100644
--- a/drivers/gpu/drm/radeon/radeon_gem.c
+++ b/drivers/gpu/drm/radeon/radeon_gem.c
@@ -428,7 +428,6 @@ int radeon_gem_mmap_ioctl(struct drm_device *dev, void 
*data,
 int radeon_gem_busy_ioctl(struct drm_device *dev, void *data,
                          struct drm_file *filp)
 {
-       struct radeon_device *rdev = dev->dev_private;
        struct drm_radeon_gem_busy *args = data;
        struct drm_gem_object *gobj;
        struct radeon_bo *robj;
@@ -440,10 +439,16 @@ int radeon_gem_busy_ioctl(struct drm_device *dev, void 
*data,
                return -ENOENT;
        }
        robj = gem_to_radeon_bo(gobj);
-       r = radeon_bo_wait(robj, &cur_placement, true);
+
+       r = reservation_object_test_signaled_rcu(robj->tbo.resv, true);
+       if (r == 0)
+               r = -EBUSY;
+       else
+               r = 0;
+
+       cur_placement = ACCESS_ONCE(robj->tbo.mem.mem_type);
        args->domain = radeon_mem_type_to_domain(cur_placement);
        drm_gem_object_unreference_unlocked(gobj);
-       r = radeon_gem_handle_lockup(rdev, r);
        return r;
 }

-- 
1.9.1