Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964916AbbLVUNm (ORCPT ); Tue, 22 Dec 2015 15:13:42 -0500 Received: from vulcan.natalenko.name ([104.207.131.136]:37898 "EHLO vulcan.natalenko.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932451AbbLVUNj convert rfc822-to-8bit (ORCPT ); Tue, 22 Dec 2015 15:13:39 -0500 DMARC-Filter: OpenDMARC Filter v1.3.1 vulcan.natalenko.name 5E7366F810 Authentication-Results: vulcan.natalenko.name; dmarc=none header.from=natalenko.name From: Oleksandr Natalenko To: Yuchung Cheng Cc: netdev , "linux-kernel@vger.kernel.org" , Patrick McHardy , Hideaki YOSHIFUJI , James Morris , Alexey Kuznetsov , "David S. Miller" Subject: Re: [REGRESSION] tcp/ipv4: kernel panic because of (possible) division by zero Date: Tue, 22 Dec 2015 22:13:36 +0200 Message-ID: <5433032.ornV7UU4Xc@spock> User-Agent: KMail/5.1 (Linux/4.3.0-pf3; KDE/5.17.0; x86_64; ; ) In-Reply-To: References: <26396443.iDTTxgChSj@spock> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1622 Lines: 44 That is correct, I have net.ipv4.tcp_ecn set to 1. I've recompiled the kernel with proposed patch, now still waiting for issue to be triggered. Could I manually simulate the erroneous TCP ECN behavior to speed up the debugging? On понеділок, 21 грудня 2015 р. 18:10:32 EET Yuchung Cheng wrote: > On Mon, Dec 21, 2015 at 12:25 PM, Oleksandr Natalenko > > wrote: > > Commit 3759824da87b30ce7a35b4873b62b0ba38905ef5 (tcp: PRR uses CRB mode by > > default and SS mode conditionally) introduced changes to > > net/ipv4/tcp_input.c tcp_cwnd_reduction() that, possibly, cause division > > by zero, and therefore, kernel panic in interrupt handler [1]. > > > > Reverting 3759824da87b30ce7a35b4873b62b0ba38905ef5 seems to fix the issue. > > > > I'm able to reproduce the issue on 4.3.0–4.3.3 once per several day > > (occasionally). > > > > What could be done to help in debugging this issue? > > Do you have ECN enabled (i.e. sysctl net.ipv4.tcp_ecn > 0)? > > If so I suspect an ACK carrying ECE during CA_Loss causes entering CWR > state w/o calling tcp_init_cwnd_reduct() to set tp->prior_cwnd. Can > you try this debug / quick-fix patch and send me the error message if > any? > > > Regards, > > > > Oleksandr. > > > > [1] http://i.piccy.info/ > > i9/6f5cb187c4ff282d189f78c63f95af43/1450729403/283985/951663/panic.jpg -- 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/