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 :)
+/**
- 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 chris@chris-wilson.co.uk -Chris