xsk: fix poll/POLLIN premature returns

Polling for the ingress queues relies on reading the producer/consumer
pointers of the Rx queue.

Prior this commit, a cached consumer pointer could be used, instead of
the actual consumer pointer and therefore report POLLIN prematurely.

This patch makes sure that the non-cached consumer pointer is used
instead.

Reported-by: Qi Zhang <[e-mail]>
Tested-by: Qi Zhang <[e-mail]>
Fixes: c497176cb2e4 ("xsk: add Rx receive functions and poll support")
Signed-off-by: Björn Töpel <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>

net/xdp/xsk_queue.h

···
 
 static inline bool xskq_empty_desc(struct xsk_queue *q)
 {
-	return xskq_nb_free(q, q->prod_tail, 1) == q->nentries;
+	return xskq_nb_free(q, q->prod_tail, q->nentries) == q->nentries;
 }
 
 void xskq_set_umem(struct xsk_queue *q, struct xdp_umem_props *umem_props);