From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f44.google.com (mail-ee0-f44.google.com [74.125.83.44]) by kanga.kvack.org (Postfix) with ESMTP id 78F836B0037 for ; Tue, 29 Apr 2014 15:19:56 -0400 (EDT) Received: by mail-ee0-f44.google.com with SMTP id c41so626254eek.17 for ; Tue, 29 Apr 2014 12:19:55 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTP id y41si28011145eel.320.2014.04.29.12.19.53 for ; Tue, 29 Apr 2014 12:19:54 -0700 (PDT) Date: Tue, 29 Apr 2014 15:19:10 -0400 From: Rik van Riel Subject: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Message-ID: <20140429151910.53f740ef@annuminas.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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/ . Don't email: email@kvack.org