NFS: Fix a bogus warning in nfs_generic_pgio

It is OK for pageused == pagecount in the loop, as long as we don't add
another entry to the *pages array. Move the test so that it only triggers
in that case.

Reported-by: Steve Dickson <SteveD@redhat.com>
Fixes: bba5c1887a (nfs: disallow duplicate pages in pgio page vectors)
Cc: Weston Andros Adamson <dros@primarydata.com>
Cc: stable@vger.kernel.org # 3.16.x
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/pagelist.c

@@ -752,12 +752,11 @@ int nfs_generic_pgio(struct nfs_pageio_descriptor *desc,
 		nfs_list_remove_request(req);
 		nfs_list_add_request(req, &hdr->pages);
 
-		if (WARN_ON_ONCE(pageused >= pagecount))
-			return nfs_pgio_error(desc, hdr);
-
 		if (!last_page || last_page != req->wb_page) {
-			*pages++ = last_page = req->wb_page;
 			pageused++;
+			if (pageused > pagecount)
+				break;
+			*pages++ = last_page = req->wb_page;
 		}
 	}
 	if (WARN_ON_ONCE(pageused != pagecount))