xprtrdma: Improve commentary around rpcrdma_reps_unmap()

Signed-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/xprtrdma/verbs.c

@@ -1041,6 +1041,10 @@ static void rpcrdma_rep_put(struct rpcrdma_buffer *buf,
 	llist_add(&rep->rr_node, &buf->rb_free_reps);
 }
 
+/* Caller must ensure the QP is quiescent (RQ is drained) before
+ * invoking this function, to guarantee rb_all_reps is not
+ * changing.
+ */
 static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt)
 {
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
@@ -1048,7 +1052,7 @@ static void rpcrdma_reps_unmap(struct rpcrdma_xprt *r_xprt)
 
 	list_for_each_entry(rep, &buf->rb_all_reps, rr_all) {
 		rpcrdma_regbuf_dma_unmap(rep->rr_rdmabuf);
-		rep->rr_temp = true;
+		rep->rr_temp = true;	/* Mark this rep for destruction */
 	}
 }