From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 7F2986B0069 for ; Mon, 7 Nov 2011 04:17:21 -0500 (EST) Date: Mon, 7 Nov 2011 17:17:04 +0800 From: Wu Fengguang Subject: Re: Possible usage of uninitalized task_ratelimit variable in mm/page-writeback.c Message-ID: <20111107091704.GA29562@localhost> References: <20111107081824.GA18221@smp.if.uj.edu.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20111107081824.GA18221@smp.if.uj.edu.pl> Sender: owner-linux-mm@kvack.org List-ID: To: Witold Baryluk Cc: "linux-mm@kvack.org" , linux-fsdevel@vger.kernel.org On Mon, Nov 07, 2011 at 04:18:24PM +0800, Witold Baryluk wrote: > Hi, > > I found a minor issue when compiling kernel today > > > CC mm/page-writeback.o > mm/page-writeback.c: In function a??balance_dirty_pages_ratelimited_nra??: > include/trace/events/writeback.h:281:1: warning: a??task_ratelimita?? may be used uninitialized in this function [-Wuninitialized] > mm/page-writeback.c:1018:16: note: a??task_ratelimita?? was declared here > > Indeed in balance_dirty_pages a task_ratelimit may be not initialized > (initialization skiped by goto pause;), and then used when calling > tracing hook. Witold, thanks for the report! This patch should fix the bug. Thanks, Fengguang --- writeback: fix uninitialized task_ratelimit In balance_dirty_pages() task_ratelimit may be not initialized (initialization skiped by goto pause;), and then used when calling tracing hook. Fix it by moving the task_ratelimit assignment before goto pause. Reported-by: Witold Baryluk Signed-off-by: Wu Fengguang --- mm/page-writeback.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- linux.orig/mm/page-writeback.c 2011-11-07 17:07:04.080000043 +0800 +++ linux/mm/page-writeback.c 2011-11-07 17:08:43.232000031 +0800 @@ -1097,13 +1097,13 @@ static void balance_dirty_pages(struct a pos_ratio = bdi_position_ratio(bdi, dirty_thresh, background_thresh, nr_dirty, bdi_thresh, bdi_dirty); - if (unlikely(pos_ratio == 0)) { + task_ratelimit = (u64)dirty_ratelimit * + pos_ratio >> RATELIMIT_CALC_SHIFT; + if (unlikely(task_ratelimit == 0)) { pause = max_pause; goto pause; } - task_ratelimit = (u64)dirty_ratelimit * - pos_ratio >> RATELIMIT_CALC_SHIFT; - pause = (HZ * pages_dirtied) / (task_ratelimit | 1); + pause = (HZ * pages_dirtied) / task_ratelimit; if (unlikely(pause <= 0)) { trace_balance_dirty_pages(bdi, dirty_thresh, -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org