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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2FB63C433EF for ; Fri, 12 Nov 2021 20:00:24 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 A1C35610A5 for ; Fri, 12 Nov 2021 20:00:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A1C35610A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=yandex-team.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:59696 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mlcik-0007WZ-Nv for qemu-devel@archiver.kernel.org; Fri, 12 Nov 2021 15:00:22 -0500 Received: from eggs.gnu.org ([209.51.188.92]:36322) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mlchv-0006g0-Gm; Fri, 12 Nov 2021 14:59:32 -0500 Received: from forwardcorp1p.mail.yandex.net ([77.88.29.217]:39360) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mlchn-0002du-AQ; Fri, 12 Nov 2021 14:59:28 -0500 Received: from sas1-4cbebe29391b.qloud-c.yandex.net (sas1-4cbebe29391b.qloud-c.yandex.net [IPv6:2a02:6b8:c08:789:0:640:4cbe:be29]) by forwardcorp1p.mail.yandex.net (Yandex) with ESMTP id 41FA32E1273; Fri, 12 Nov 2021 22:59:18 +0300 (MSK) Received: from myt5-70c90f7d6d7d.qloud-c.yandex.net (myt5-70c90f7d6d7d.qloud-c.yandex.net [2a02:6b8:c12:3e2c:0:640:70c9:f7d]) by sas1-4cbebe29391b.qloud-c.yandex.net (mxbackcorp/Yandex) with ESMTP id rhOtb5Vzff-xGsaqB15; Fri, 12 Nov 2021 22:59:18 +0300 Precedence: bulk DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1636747158; bh=EyVHS8E4c2j7QyDfgjw3yvYNlFMalNlDirV6vad05Dg=; h=In-Reply-To:Subject:To:From:Message-ID:Cc:References:Date; b=bZEBb9t6jiXNVs08HIiKYysfVCgtawF9IsHuDHvRwjc0pd/yjvrwfZJ2cte3fOye5 x9dlLcCAMJWwa0vnhldq8JzWhmZPuaD4mE/qcgkHPUX7me8gS7V7gqhXh/X8IdDCK3 Xt9/Q7egF3IXh1fHhKyyGGp8mmp+/1iyfI0swCtI= Authentication-Results: sas1-4cbebe29391b.qloud-c.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from rvkaganb.lan (dynamic-vpn.dhcp.yndx.net [2a02:6b8:b081:1206::1:19]) by myt5-70c90f7d6d7d.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPS id sDrSepsqEf-xGxaQYeL; Fri, 12 Nov 2021 22:59:16 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) X-Yandex-Fwd: 2 Date: Fri, 12 Nov 2021 22:59:14 +0300 From: Roman Kagan To: Kevin Wolf Subject: Re: [PATCH 01/10] vhost-user-blk: reconnect on any error during realize Message-ID: Mail-Followup-To: Roman Kagan , Kevin Wolf , qemu-devel@nongnu.org, qemu-block@nongnu.org, "Michael S. Tsirkin" , Hanna Reitz , yc-core@yandex-team.ru, =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Paolo Bonzini References: <20211111153354.18807-1-rvkagan@yandex-team.ru> <20211111153354.18807-2-rvkagan@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=77.88.29.217; envelope-from=rvkagan@yandex-team.ru; helo=forwardcorp1p.mail.yandex.net X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-block@nongnu.org, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Hanna Reitz , yc-core@yandex-team.ru, Paolo Bonzini , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Nov 12, 2021 at 12:37:59PM +0100, Kevin Wolf wrote: > Am 12.11.2021 um 08:39 hat Roman Kagan geschrieben: > > On Thu, Nov 11, 2021 at 06:52:30PM +0100, Kevin Wolf wrote: > > > Am 11.11.2021 um 16:33 hat Roman Kagan geschrieben: > > > > vhost-user-blk realize only attempts to reconnect if the previous > > > > connection attempt failed on "a problem with the connection and not an > > > > error related to the content (which would fail again the same way in the > > > > next attempt)". > > > > > > > > However this distinction is very subtle, and may be inadvertently broken > > > > if the code changes somewhere deep down the stack and a new error gets > > > > propagated up to here. > > > > > > > > OTOH now that the number of reconnection attempts is limited it seems > > > > harmless to try reconnecting on any error. > > > > > > > > So relax the condition of whether to retry connecting to check for any > > > > error. > > > > > > > > This patch amends a527e312b5 "vhost-user-blk: Implement reconnection > > > > during realize". > > > > > > > > Signed-off-by: Roman Kagan > > > > > > It results in less than perfect error messages. With a modified export > > > that just crashes qemu-storage-daemon during get_features, I get: > > > > > > qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Failed to read msg header. Read 0 instead of 12. Original request 1. > > > qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after error: vhost_backend_init failed: Protocol error > > > qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after error: Failed to connect to '/tmp/vsock': Connection refused > > > qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Reconnecting after error: Failed to connect to '/tmp/vsock': Connection refused > > > qemu-system-x86_64: -device vhost-user-blk-pci,chardev=c: Failed to connect to '/tmp/vsock': Connection refused > > > > This patch doesn't change any error messages. Which ones specifically > > became less than perfect as a result of this patch? > > But it adds error messages (for each retry), which are different from > the first error message. As I said this is not the end of the world, but > maybe a bit more confusing. Ah, now I see what you mean: it adds reconnection attempts where there used to be immediate failure return, so now every failed attempt logs its own message. > > > I guess this might be tolerable. On the other hand, the patch doesn't > > > really fix anything either, but just gets rid of possible subtleties. > > > > The remaining patches in the series make other errors beside -EPROTO > > propagate up to this point, and some (most) of them are retryable. This > > was the reason to include this patch at the beginning of the series (I > > guess I should've mentioned that in the patch log). > > I see. I hadn't looked at the rest of the series yet because I ran out > of time, but now that I'm skimming them, I see quite a few places that > use non-EPROTO, but I wonder which of them actually should be > reconnected. So far all I saw were presumably persistent errors where a > retry won't help. Can you give me some examples? E.g. the particular case you mention earlier, -ECONNREFUSED, is not unlikely to happen due to the vhost-user server restart for maintenance; in this case retying looks like a reasonable thing to do, doesn't it? Thanks, Roman.