svcrdma: Convert "might sleep" comment into a code annotation

Try to catch incorrect calling contexts mechanically rather than by
code review.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Tom Talpey <tom@talpey.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/xprtrdma/svc_rdma_rw.c

@@ -353,8 +353,7 @@ static void svc_rdma_wc_read_done(struct ib_cq *cq, struct ib_wc *wc)
 	return;
 }
 
-/* This function sleeps when the transport's Send Queue is congested.
- *
+/*
  * Assumptions:
  * - If ib_post_send() succeeds, only one completion is expected,
  *   even if one or more WRs are flushed. This is true when posting
@@ -369,6 +368,8 @@ static int svc_rdma_post_chunk_ctxt(struct svc_rdma_chunk_ctxt *cc)
 	struct ib_cqe *cqe;
 	int ret;
 
+	might_sleep();
+
 	if (cc->cc_sqecount > rdma->sc_sq_depth)
 		return -EINVAL;
 

net/sunrpc/xprtrdma/svc_rdma_sendto.c

@@ -315,6 +315,8 @@ int svc_rdma_send(struct svcxprt_rdma *rdma, struct svc_rdma_send_ctxt *ctxt)
 	struct ib_send_wr *wr = &ctxt->sc_send_wr;
 	int ret;
 
+	might_sleep();
+
 	/* Sync the transport header buffer */
 	ib_dma_sync_single_for_device(rdma->sc_pd->device,
 				      wr->sg_list[0].addr,