Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755705AbaFJUBk (ORCPT ); Tue, 10 Jun 2014 16:01:40 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35572 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753878AbaFJTxs (ORCPT ); Tue, 10 Jun 2014 15:53:48 -0400 From: Kamal Mostafa 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 , Kamal Mostafa Subject: [PATCH 3.13 156/160] mm/page-writeback.c: fix divide by zero in pos_ratio_polynom Date: Tue, 10 Jun 2014 12:46:36 -0700 Message-Id: <1402429600-20477-157-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1402429600-20477-1-git-send-email-kamal@canonical.com> References: <1402429600-20477-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.13.11.3 -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 Signed-off-by: Kamal Mostafa --- mm/page-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 7106cb1..8f6daa6 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) * => fast response on large errors; small oscillation near setpoint */ -static inline long long pos_ratio_polynom(unsigned long setpoint, +static long long pos_ratio_polynom(unsigned long setpoint, unsigned long dirty, unsigned long limit) { long long pos_ratio; long x; - 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; @@ -842,7 +842,7 @@ 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/