From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752864AbaFGBab (ORCPT ); Fri, 6 Jun 2014 21:30:31 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36108 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752675AbaFGBXj (ORCPT ); Fri, 6 Jun 2014 21:23:39 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Michal Hocko" , "Aneesh Kumar K.V" , "Rik van Riel" , "Nishanth Aravamudan" , "Masayoshi Mizuma" , "Mel Gorman" , "Linus Torvalds" , "Luiz Capitulino" Date: Sat, 07 Jun 2014 02:26:29 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 60/92] mm/page-writeback.c: fix divide by zero in pos_ratio_polynom In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Rik van Riel commit d5c9fde3dae750889168807038243ff36431d276 upstream. It is possible for "limit - setpoint + 1" to equal zero, after getting truncated to a 32 bit variable, and resulting in a divide by zero error. Using the fully 64 bit divide functions avoids this problem. It also will cause pos_ratio_polynom() to return the correct value when (setpoint - limit) exceeds 2^32. Also uninline pos_ratio_polynom, at Andrew's request. Signed-off-by: Rik van Riel Reviewed-by: Michal Hocko Cc: Aneesh Kumar K.V Cc: Mel Gorman Cc: Nishanth Aravamudan Cc: Luiz Capitulino Cc: Masayoshi Mizuma Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: Adjust context - pos_ratio_polynom() is not a separate function] Signed-off-by: Ben Hutchings --- mm/page-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -559,7 +559,7 @@ static unsigned long bdi_position_ratio( * => fast response on large errors; small oscillation near setpoint */ setpoint = (freerun + limit) / 2; - x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, limit - setpoint + 1); pos_ratio = x; pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; @@ -625,7 +625,7 @@ static unsigned long bdi_position_ratio( x_intercept = bdi_setpoint + span; if (bdi_dirty < x_intercept - span / 4) { - pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), x_intercept - bdi_setpoint + 1); } else pos_ratio /= 4;