From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759382AbaGRGyt (ORCPT ); Fri, 18 Jul 2014 02:54:49 -0400 Received: from mail-wg0-f49.google.com ([74.125.82.49]:65230 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758919AbaGRGyr (ORCPT ); Fri, 18 Jul 2014 02:54:47 -0400 Date: Fri, 18 Jul 2014 08:54:44 +0200 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Johannes Weiner , Rik van Riel , stable@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch] mm, writeback: prevent race when calculating dirty limits Message-ID: <20140718065444.GA21453@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 16-07-14 17:36:49, David Rientjes wrote: > 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 Makes sense to me Acked-by: Michal Hocko > --- > 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 -- Michal Hocko SUSE Labs