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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 956B1C2D0E4 for ; Tue, 24 Nov 2020 08:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 202F12073C for ; Tue, 24 Nov 2020 08:58:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eD7NCZxb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730932AbgKXI5l (ORCPT ); Tue, 24 Nov 2020 03:57:41 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39221 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730896AbgKXI5k (ORCPT ); Tue, 24 Nov 2020 03:57:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606208258; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xJwIP3nSo2Uj/Swvhl1TAV1Y63wZ0HYh6rGKpKJBlYE=; b=eD7NCZxbmxC7qf1Spt8mQGCl/9DGZLhTvK8ATAzecjPZrCzPARWpVdKhumZXRYy1PiXatM fGtfS+4r7qKilSzBJJXNwxNeypoi7XUvmmhWwqt37b02icgYCcnyUaVqpJvznQMzL9v4z3 ZnJZCj17+ff4vnnRQWhM1jl2YZL0gKY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-373-AYv1W39-MCqm9Pn8IDBYPw-1; Tue, 24 Nov 2020 03:57:34 -0500 X-MC-Unique: AYv1W39-MCqm9Pn8IDBYPw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D8383A0BD4; Tue, 24 Nov 2020 08:57:31 +0000 (UTC) Received: from [10.72.13.120] (ovpn-13-120.pek2.redhat.com [10.72.13.120]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0D64160C13; Tue, 24 Nov 2020 08:57:24 +0000 (UTC) Subject: Re: netconsole deadlock with virtnet To: Leon Romanovsky Cc: Jakub Kicinski , Steven Rostedt , Sergey Senozhatsky , "Michael S. Tsirkin" , Petr Mladek , John Ogness , virtualization@lists.linux-foundation.org, Amit Shah , Itay Aveksis , Ran Rozenstein , netdev References: <93b42091-66f2-bb92-6822-473167b2698d@redhat.com> <20201118091257.2ee6757a@gandalf.local.home> <20201123110855.GD3159@unreal> <20201123093128.701cf81b@gandalf.local.home> <20201123105252.1c295138@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <20201123140934.38748be3@gandalf.local.home> <20201123112130.759b9487@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <1133f1a4-6772-8aa3-41dd-edbc1ee76cee@redhat.com> <20201124080152.GG3159@unreal> From: Jason Wang Message-ID: <6f046c51-cdcc-77f9-4859-2508d08126f8@redhat.com> Date: Tue, 24 Nov 2020 16:57:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201124080152.GG3159@unreal> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/11/24 下午4:01, Leon Romanovsky wrote: > On Tue, Nov 24, 2020 at 11:22:03AM +0800, Jason Wang wrote: >> On 2020/11/24 上午3:21, Jakub Kicinski wrote: >>> On Mon, 23 Nov 2020 14:09:34 -0500 Steven Rostedt wrote: >>>> On Mon, 23 Nov 2020 10:52:52 -0800 >>>> Jakub Kicinski wrote: >>>> >>>>> On Mon, 23 Nov 2020 09:31:28 -0500 Steven Rostedt wrote: >>>>>> On Mon, 23 Nov 2020 13:08:55 +0200 >>>>>> Leon Romanovsky wrote: >>>>>> >>>>>>> [ 10.028024] Chain exists of: >>>>>>> [ 10.028025] console_owner --> target_list_lock --> _xmit_ETHER#2 >>>>>> Note, the problem is that we have a location that grabs the xmit_lock while >>>>>> holding target_list_lock (and possibly console_owner). >>>>> Well, it try_locks the xmit_lock. Does lockdep understand try-locks? >>>>> >>>>> (not that I condone the shenanigans that are going on here) >>>> Does it? >>>> >>>> virtnet_poll_tx() { >>>> __netif_tx_lock() { >>>> spin_lock(&txq->_xmit_lock); >>> Umpf. Right. I was looking at virtnet_poll_cleantx() >>> >>>> That looks like we can have: >>>> >>>> >>>> CPU0 CPU1 >>>> ---- ---- >>>> lock(xmit_lock) >>>> >>>> lock(console) >>>> lock(target_list_lock) >>>> __netif_tx_lock() >>>> lock(xmit_lock); >>>> >>>> [BLOCKED] >>>> >>>> >>>> lock(console) >>>> >>>> [BLOCKED] >>>> >>>> >>>> >>>> DEADLOCK. >>>> >>>> >>>> So where is the trylock here? >>>> >>>> Perhaps you need the trylock in virtnet_poll_tx()? >>> That could work. Best if we used normal lock if !!budget, and trylock >>> when budget is 0. But maybe that's too hairy. >> >> If we use trylock, we probably lose(or delay) tx notification that may have >> side effects to the stack. >> >> >>> I'm assuming all this trickiness comes from virtqueue_get_buf() needing >>> locking vs the TX path? It's pretty unusual for the completion path to >>> need locking vs xmit path. >> >> Two reasons for doing this: >> >> 1) For some historical reason, we try to free transmitted tx packets in xmit >> (see free_old_xmit_skbs() in start_xmit()), we can probably remove this if >> we remove the non tx interrupt mode. >> 2) virtio core requires virtqueue_get_buf() to be synchronized with >> virtqueue_add(), we probably can solve this but it requires some non trivial >> refactoring in the virtio core > So how will we solve our lockdep issues? > > Thanks It's not clear to me that whether it's a virtio-net specific issue. E.g the above deadlock looks like a generic issue so workaround it via virtio-net may not help for other drivers. Thanks > >> Btw, have a quick search, there are several other drivers that uses tx lock >> in the tx NAPI. >> >> Thanks >>