Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755067AbaFWNIm (ORCPT ); Mon, 23 Jun 2014 09:08:42 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:37242 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754877AbaFWNFZ (ORCPT ); Mon, 23 Jun 2014 09:05:25 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Rik van Riel , "Aneesh Kumar K.V" , Mel Gorman , Nishanth Aravamudan , Luiz Capitulino , Masayoshi Mizuma , Andrew Morton , Linus Torvalds , Ben Hutchings , Luis Henriques Subject: [PATCH 3.11 79/93] mm/page-writeback.c: fix divide by zero in pos_ratio_polynom Date: Mon, 23 Jun 2014 14:02:58 +0100 Message-Id: <1403528592-2163-80-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1403528592-2163-1-git-send-email-luis.henriques@canonical.com> References: <1403528592-2163-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.11.10.12 -stable 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 Signed-off-by: Luis Henriques --- mm/page-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 7298e741ae35..ad494ae5703f 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -689,7 +689,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, * => 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; @@ -755,7 +755,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, 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; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/