On Fri, Sep 01, 2017 at 03:57:06PM +0100, Chris Wilson wrote:
> We take advantage of that syncobj->fence is an RCU-protected pointer, and
> so sparse complains that it is lacking annotation.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> include/drm/drm_syncobj.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
> index c00fee539822..455660673259 100644
> --- a/include/drm/drm_syncobj.h
> +++ b/include/drm/drm_syncobj.h
> @@ -49,7 +49,7 @@ struct drm_syncobj {
> * This field should not be used directly. Use drm_syncobj_fence_get
> * and drm_syncobj_replace_fence instead.
> */
> - struct dma_fence *fence;
> + struct dma_fence __rcu *fence;
drm_syncobj.c uses that pointer directly quite a bit which seems to
generate more sparse warnings.
Would something like this be needed (just typing stuff blindly here)?
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 0422b8c2c2e7..1786787ecc30 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -106,7 +106,8 @@ static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
* callback when a fence has already been set.
*/
if (syncobj->fence) {
- *fence = dma_fence_get(syncobj->fence);
+ *fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+ lockdep_is_held(&syncobj->lock)));
ret = 1;
} else {
*fence = NULL;
@@ -168,8 +169,9 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
spin_lock(&syncobj->lock);
- old_fence = syncobj->fence;
- syncobj->fence = fence;
+ old_fence = rcu_dereference_protected(syncobj->fence,
+ lockdep_is_held(&syncobj->lock));
+ rcu_assign_pointer(syncobj->fence, fence);
if (fence != old_fence) {
list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node) {
@@ -613,7 +615,8 @@ static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,
container_of(cb, struct syncobj_wait_entry, syncobj_cb);
/* This happens inside the syncobj lock */
- wait->fence = dma_fence_get(syncobj->fence);
+ wait->fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+ lockdep_is_held(&syncobj->lock)));
wake_up_process(wait->task);
}
--
Ville Syrjälä
Intel OTC
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