Modify the queue APIs to protect all user space index loads
with smp_load_acquire() and all user space index stores with
smp_store_release(). Base this on the types of the queues which
can be one of ..KERNEL, ..FROM_USER, ..TO_USER. Kernel space
indices are protected by locks which also provide memory barriers.

Signed-off-by: Bob Pearson <redacted>
v2:
  In v2 use queue type to selectively protect user space indices.
 drivers/infiniband/sw/rxe/rxe_queue.h | 168 ++++++++++++++++++--------
 1 file changed, 117 insertions(+), 51 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_queue.h b/drivers/infiniband/sw/rxe/rxe_queue.h
index 4512745419f8..6e705e09d357 100644
+++ b/drivers/infiniband/sw/rxe/rxe_queue.h

@@ -66,12 +66,22 @@ static inline int queue_empty(struct rxe_queue *q)
 	u32 prod;
 	u32 cons;
 
-	/* make sure all changes to queue complete before
-	 * testing queue empty
-	 */
-	prod = smp_load_acquire(&q->buf->producer_index);
-	/* same */
-	cons = smp_load_acquire(&q->buf->consumer_index);
+	switch (q->type) {
+	case QUEUE_TYPE_FROM_USER:
+		/* protect user space index */
+		prod = smp_load_acquire(&q->buf->producer_index);
+		cons = q->buf->consumer_index;