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 D53B6C2D0E4 for ; Tue, 24 Nov 2020 03:22:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5EDFE2085B for ; Tue, 24 Nov 2020 03:22:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="g6B75bIa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729018AbgKXDWV (ORCPT ); Mon, 23 Nov 2020 22:22:21 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:32025 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726964AbgKXDWV (ORCPT ); Mon, 23 Nov 2020 22:22:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606188139; 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=q/cB4Y6zYi35tKuoN6G4/JIJq3FZA+1nclYd1TtN7K0=; b=g6B75bIaNbqnxqU1X6hesTkvX1oDJCteE61VEf//t0fdrzb86/81k43XCsCZUXVdmiyCgO fCBFWIkcB7daBI37eVS19/guWWPgYho46/Crw1hOZKfLPB+KYk27D7nYFuOufXue1ntSr4 5DtM786PGjbxDzXg8fRWo1es1DDqzII= 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-397-4hhBCgcnN-6yIxgr9mr-og-1; Mon, 23 Nov 2020 22:22:14 -0500 X-MC-Unique: 4hhBCgcnN-6yIxgr9mr-og-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 97F2110066FB; Tue, 24 Nov 2020 03:22:12 +0000 (UTC) Received: from [10.72.13.198] (ovpn-13-198.pek2.redhat.com [10.72.13.198]) by smtp.corp.redhat.com (Postfix) with ESMTP id 19D43620DE; Tue, 24 Nov 2020 03:22:04 +0000 (UTC) Subject: Re: netconsole deadlock with virtnet To: Jakub Kicinski , Steven Rostedt Cc: Leon Romanovsky , Sergey Senozhatsky , "Michael S. Tsirkin" , Petr Mladek , John Ogness , virtualization@lists.linux-foundation.org, Amit Shah , Itay Aveksis , Ran Rozenstein , netdev References: <20201117102341.GR47002@unreal> <20201117093325.78f1486d@gandalf.local.home> <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> From: Jason Wang Message-ID: <1133f1a4-6772-8aa3-41dd-edbc1ee76cee@redhat.com> Date: Tue, 24 Nov 2020 11:22:03 +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: <20201123112130.759b9487@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 Btw, have a quick search, there are several other drivers that uses tx lock in the tx NAPI. Thanks >