Am 06.08.19 um 21:24 schrieb Chris Wilson:
Quoting Christian König (2019-08-06 16:01:33)
Add a new helper to get a consistent set of pointers from the reservation
object. While at it group all access helpers together in the header file.
Ah, needs to be earlier :)
Ah, crap. That got incorrectly reordered while moving the fixes to the
beginning of the set.
+/**
+ * reservation_object_fences - read consistent fence pointers
+ * @obj: reservation object where we get the fences from
+ * @excl: pointer for the exclusive fence
+ * @list: pointer for the shared fence list
+ *
+ * Make sure we have a consisten exclusive fence and shared fence list.
+ * Must be called with rcu read side lock held.
+ */
+static inline void
+reservation_object_fences(struct reservation_object *obj,
+ struct dma_fence **excl,
+ struct reservation_object_list **list)
+{
+ unsigned int seq;
+
+ do {
+ seq = read_seqcount_begin(&obj->seq);
+ *excl = rcu_dereference(obj->fence_excl);
+ *list = rcu_dereference(obj->fence);
+ } while (read_seqcount_retry(&obj->seq, seq));
+}
I would personally prefer return excl rather than have it as a second
outparam, but I'd leave that to gcc to decide.
Having stared at this, I agree this does the right thing. The important
point from all callers' perspective is that the combination of pointers
is consistent for this rcu_read_lock. And rcu_dereference enforces the
callers do hold rcu_read_lock.
I didn't check all the conversions, just stared at the heart of the
problem.
Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk>
Thanks.
Going to fix that up,
Christian.
-Chris
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