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authorJason Ekstrand <jason@jlekstrand.net>2017-08-25 20:52:20 +0300
committerDave Airlie <airlied@redhat.com>2017-08-28 23:20:30 +0300
commit309a5482fa9eb7bc754bf95a2cd89091b01c33d2 (patch)
tree0867e51139f138fa4a8824f0df52db357de77d12 /include/drm
parentafaf59237843bf89823c33143beca6b262dff0ca (diff)
downloadlinux-309a5482fa9eb7bc754bf95a2cd89091b01c33d2.tar.xz
drm/syncobj: Add a race-free drm_syncobj_fence_get helper (v2)
The atomic exchange operation in drm_syncobj_replace_fence is sufficient for the case where it races with itself. However, if you have a race between a replace_fence and dma_fence_get(syncobj->fence), you may end up with the entire replace_fence happening between the point in time where the one thread gets the syncobj->fence pointer and when it calls dma_fence_get() on it. If this happens, then the reference may be dropped before we get a chance to get a new one. The new helper uses dma_fence_get_rcu_safe to get rid of the race. This is also needed because it allows us to do a bit more than just get a reference in drm_syncobj_fence_get should we wish to do so. v2: - RCU isn't that scary - Call rcu_read_lock/unlock - Don't rename fence to _fence - Make the helper static inline Signed-off-by: Jason Ekstrand <jason@jlekstrand.net> Acked-by: Christian König <christian.koenig@amd.com> (v1) Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'include/drm')
-rw-r--r--include/drm/drm_syncobj.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
index 7d4ad777132e..ce94d14c5087 100644
--- a/include/drm/drm_syncobj.h
+++ b/include/drm/drm_syncobj.h
@@ -77,6 +77,18 @@ drm_syncobj_put(struct drm_syncobj *obj)
kref_put(&obj->refcount, drm_syncobj_free);
}
+static inline struct dma_fence *
+drm_syncobj_fence_get(struct drm_syncobj *syncobj)
+{
+ struct dma_fence *fence;
+
+ rcu_read_lock();
+ fence = dma_fence_get_rcu_safe(&syncobj->fence);
+ rcu_read_unlock();
+
+ return fence;
+}
+
struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
u32 handle);
void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,