CIFS: Fix readpages retrying on reconnects

If we got a reconnect error from async readv we re-add pages back
to page_list and continue loop. That is wrong because these pages
have been already added to the pagecache but page_list has pages that
have not been added to the pagecache yet. This ends up with a general
protection fault in put_pages after readpages. Fix it by not retrying
the read of these pages and falling back to readpage instead.

Fixes debian bug 762306
Signed-off-by: NPavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: NSteve French <smfrench@gmail.com>
Tested-by: NArthur Marsh <arthur.marsh@internode.on.net>

fs/cifs/file.c

@@ -3568,15 +3568,9 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
 				lru_cache_add_file(page);
 				unlock_page(page);
 				page_cache_release(page);
-				if (rc == -EAGAIN)
-					list_add_tail(&page->lru, &tmplist);
 			}
+			/* Fallback to the readpage in error/reconnect cases */
 			kref_put(&rdata->refcount, cifs_readdata_release);
-			if (rc == -EAGAIN) {
-				/* Re-add pages to the page_list and retry */
-				list_splice(&tmplist, page_list);
-				continue;
-			}
 			break;
 		}