Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758268AbaD2TUA (ORCPT ); Tue, 29 Apr 2014 15:20:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63838 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751837AbaD2TT7 (ORCPT ); Tue, 29 Apr 2014 15:19:59 -0400 Date: Tue, 29 Apr 2014 15:19:10 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, sandeen@redhat.com, akpm@linux-foundation.org, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, mhocko@suse.cz, fengguang.wu@intel.com, mpatlasov@parallels.com Subject: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Message-ID: <20140429151910.53f740ef@annuminas.surriel.com> Organization: Red Hat, Inc. MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It is possible for "limit - setpoint + 1" to equal zero, leading to a divide by zero error. Blindly adding 1 to "limit - setpoint" is not working, so we need to actually test the divisor before calling div64. Signed-off-by: Rik van Riel Cc: stable@vger.kernel.org --- mm/page-writeback.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index ef41349..2682516 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -597,11 +597,16 @@ static inline long long pos_ratio_polynom(unsigned long setpoint, unsigned long dirty, unsigned long limit) { + unsigned int divisor; long long pos_ratio; long x; + divisor = limit - setpoint; + if (!divisor) + divisor = 1; + x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, - limit - setpoint + 1); + divisor); pos_ratio = x; pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; -- 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/