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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6D7FBC2D0E4 for ; Tue, 24 Nov 2020 09:26:34 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C25152073C for ; Tue, 24 Nov 2020 09:26:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="2eMylOdZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C25152073C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 37857204D4; Tue, 24 Nov 2020 09:26:31 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id qQ3gVOgAhawX; Tue, 24 Nov 2020 09:26:29 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id A0576203DB; Tue, 24 Nov 2020 09:26:29 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 83D63C163C; Tue, 24 Nov 2020 09:26:29 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 72F3AC0052 for ; Tue, 24 Nov 2020 09:26:28 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 4E478204D4 for ; Tue, 24 Nov 2020 09:26:28 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xoBgzcuIrb4L for ; Tue, 24 Nov 2020 09:26:26 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by silver.osuosl.org (Postfix) with ESMTPS id 6042E203DB for ; Tue, 24 Nov 2020 09:26:26 +0000 (UTC) Received: from localhost (searspoint.nvidia.com [216.228.112.21]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EA8D32076B; Tue, 24 Nov 2020 09:26:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606209985; bh=eIrBvn6VIWhITdI4WjRtSSOqgfi0NiymQmtvmzBl3bg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=2eMylOdZtU6X8AOAcTgyLTdXy6WLXnN6oFZXs+DEEh9lpjzgjqVVx5O2kZb2bStkN /Q4/xCyLcpBQdykEOebV/RwfSRBioFTCqzqqYbkqO5SQMnsW7CPmMYoT3x0DymRzA9 SCGa6Kc6oWnyChsjbERzLAa4UZhhhDNBNgGf2v60= Date: Tue, 24 Nov 2020 11:26:21 +0200 From: Leon Romanovsky To: Jason Wang Subject: Re: netconsole deadlock with virtnet Message-ID: <20201124092621.GH3159@unreal> 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> <6f046c51-cdcc-77f9-4859-2508d08126f8@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <6f046c51-cdcc-77f9-4859-2508d08126f8@redhat.com> Cc: Petr Mladek , John Ogness , "Michael S. Tsirkin" , netdev , Amit Shah , Steven Rostedt , virtualization@lists.linux-foundation.org, Sergey Senozhatsky , Ran Rozenstein , Itay Aveksis , Jakub Kicinski X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" T24gVHVlLCBOb3YgMjQsIDIwMjAgYXQgMDQ6NTc6MjNQTSArMDgwMCwgSmFzb24gV2FuZyB3cm90 ZToKPgo+IE9uIDIwMjAvMTEvMjQg5LiL5Y2INDowMSwgTGVvbiBSb21hbm92c2t5IHdyb3RlOgo+ ID4gT24gVHVlLCBOb3YgMjQsIDIwMjAgYXQgMTE6MjI6MDNBTSArMDgwMCwgSmFzb24gV2FuZyB3 cm90ZToKPiA+ID4gT24gMjAyMC8xMS8yNCDkuIrljYgzOjIxLCBKYWt1YiBLaWNpbnNraSB3cm90 ZToKPiA+ID4gPiBPbiBNb24sIDIzIE5vdiAyMDIwIDE0OjA5OjM0IC0wNTAwIFN0ZXZlbiBSb3N0 ZWR0IHdyb3RlOgo+ID4gPiA+ID4gT24gTW9uLCAyMyBOb3YgMjAyMCAxMDo1Mjo1MiAtMDgwMAo+ 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header.b="2eMylOdZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731191AbgKXJ02 (ORCPT ); Tue, 24 Nov 2020 04:26:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:36068 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730978AbgKXJ00 (ORCPT ); Tue, 24 Nov 2020 04:26:26 -0500 Received: from localhost (searspoint.nvidia.com [216.228.112.21]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EA8D32076B; Tue, 24 Nov 2020 09:26:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606209985; bh=eIrBvn6VIWhITdI4WjRtSSOqgfi0NiymQmtvmzBl3bg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=2eMylOdZtU6X8AOAcTgyLTdXy6WLXnN6oFZXs+DEEh9lpjzgjqVVx5O2kZb2bStkN /Q4/xCyLcpBQdykEOebV/RwfSRBioFTCqzqqYbkqO5SQMnsW7CPmMYoT3x0DymRzA9 SCGa6Kc6oWnyChsjbERzLAa4UZhhhDNBNgGf2v60= Date: Tue, 24 Nov 2020 11:26:21 +0200 From: Leon Romanovsky To: Jason Wang 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 Subject: Re: netconsole deadlock with virtnet Message-ID: <20201124092621.GH3159@unreal> 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> <6f046c51-cdcc-77f9-4859-2508d08126f8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6f046c51-cdcc-77f9-4859-2508d08126f8@redhat.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Nov 24, 2020 at 04:57:23PM +0800, Jason Wang wrote: > > 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. It is hard to say, no one else complained except me who is using virtio :). Thanks > > Thanks > > > > > > > Btw, have a quick search, there are several other drivers that uses tx lock > > > in the tx NAPI. > > > > > > Thanks > > > >