From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 213ECC43331 for ; Tue, 12 Nov 2019 08:47:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 00E4521783 for ; Tue, 12 Nov 2019 08:47:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727365AbfKLIrT (ORCPT ); Tue, 12 Nov 2019 03:47:19 -0500 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:57005 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725821AbfKLIrT (ORCPT ); Tue, 12 Nov 2019 03:47:19 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R881e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=tonylu@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0ThsxEsr_1573548435; Received: from localhost(mailfrom:tonylu@linux.alibaba.com fp:SMTPD_---0ThsxEsr_1573548435) by smtp.aliyun-inc.com(127.0.0.1); Tue, 12 Nov 2019 16:47:15 +0800 Date: Tue, 12 Nov 2019 16:47:14 +0800 From: Tony Lu To: Cong Wang Cc: David Miller , shemminger@osdl.org, Linux Kernel Network Developers , LKML Subject: Re: [PATCH] net: remove static inline from dev_put/dev_hold Message-ID: <20191112084714.GC67139@TonyMac-Alibaba> Reply-To: Tony Lu References: <20191111140502.17541-1-tonylu@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 11, 2019 at 01:26:13PM -0800, Cong Wang wrote: > On Mon, Nov 11, 2019 at 6:12 AM Tony Lu wrote: > > > > This patch removes static inline from dev_put/dev_hold in order to help > > trace the pcpu_refcnt leak of net_device. > > > > We have sufferred this kind of issue for several times during > > manipulating NIC between different net namespaces. It prints this > > log in dmesg: > > > > unregister_netdevice: waiting for eth0 to become free. Usage count = 1 > > I debugged a nasty dst refcnt leak in TCP a long time ago, so I can > feel your pain. > > > > > > However, it is hard to find out who called and leaked refcnt in time. It > > only left the crime scene but few evidence. Once leaked, it is not > > safe to fix it up on the running host. We can't trace dev_put/dev_hold > > directly, for the functions are inlined and used wildly amoung modules. > > And this issue is common, there are tens of patches fix net_device > > refcnt leak for various causes. > > > > To trace the refcnt manipulating, this patch removes static inline from > > dev_put/dev_hold. We can use handy tools, such as eBPF with kprobe, to > > find out who holds but forgets to put refcnt. This will not be called > > frequently, so the overhead is limited. > > I think tracepoint serves the purpose of tracking function call history, > you can add tracepoint for each of dev_put()/dev_hold(), which could > also inherit the trace filter and trigger too. Thanks for your advice. I already made a patch set to add a pair of tracepoints to trace dev_hold()/dev_put() as an available solution. I used to want to give a flexible approach for people who want to choose. I will send it out later. > > The netdev refcnt itself is not changed very frequently, but it is > refcnt'ed by other things like dst too which is changed frequently. > This is why usually when you see the netdev refcnt leak warning, > the problem is probably somewhere else, like dst refcnt leak. We also suffered dst refcnt leak issue before. It is really hard to investigate. I will think about this place well. > > Hope this helps. > > Thanks. Thanks. Tony Lu