From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754966AbaGQAgx (ORCPT ); Wed, 16 Jul 2014 20:36:53 -0400 Received: from mail-ig0-f175.google.com ([209.85.213.175]:60963 "EHLO mail-ig0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752627AbaGQAgw (ORCPT ); Wed, 16 Jul 2014 20:36:52 -0400 Date: Wed, 16 Jul 2014 17:36:49 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Andrew Morton cc: Johannes Weiner , Michal Hocko , Rik van Riel , stable@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [patch] mm, writeback: prevent race when calculating dirty limits Message-ID: User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Setting vm_dirty_bytes and dirty_background_bytes is not protected by any serialization. Therefore, it's possible for either variable to change value after the test in global_dirty_limits() to determine whether available_memory needs to be initialized or not. Always ensure that available_memory is properly initialized. Cc: stable@vger.kernel.org Signed-off-by: David Rientjes --- mm/page-writeback.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -261,14 +261,11 @@ static unsigned long global_dirtyable_memory(void) */ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) { + const unsigned long available_memory = global_dirtyable_memory(); unsigned long background; unsigned long dirty; - unsigned long uninitialized_var(available_memory); struct task_struct *tsk; - if (!vm_dirty_bytes || !dirty_background_bytes) - available_memory = global_dirtyable_memory(); - if (vm_dirty_bytes) dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE); else