cifs: Fix kmap_local_page() unmapping

kmap_local_page() requires kunmap_local() to unmap the mapping.  In
addition memcpy_page() is provided to perform this common memcpy
pattern.

Replace the kmap_local_page() and broken kunmap() with memcpy_page()

Fixes: d406d267 ("cifs: skip alloc when request has no pages")
Reviewed-by: Paulo Alcantara <pc@cjr.nz>
Reviewed-by: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -4488,17 +4488,12 @@ smb3_init_transform_rq(struct TCP_Server_Info *server, int num_rqst,
 
 		/* copy pages form the old */
 		for (j = 0; j < npages; j++) {
-			char *dst, *src;
 			unsigned int offset, len;
 
 			rqst_page_get_length(new, j, &len, &offset);
 
-			dst = kmap_local_page(new->rq_pages[j]) + offset;
-			src = kmap_local_page(old->rq_pages[j]) + offset;
-
-			memcpy(dst, src, len);
-			kunmap(new->rq_pages[j]);
-			kunmap(old->rq_pages[j]);
+			memcpy_page(new->rq_pages[j], offset,
+				    old->rq_pages[j], offset, len);
 		}
 	}