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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 9E353C12002 for ; Wed, 21 Jul 2021 16:03:13 +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 3F88960D07 for ; Wed, 21 Jul 2021 16:03:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F88960D07 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34396 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m6Egh-00062k-Tl for qemu-devel@archiver.kernel.org; Wed, 21 Jul 2021 12:03:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41210) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m6Ede-00037c-BV for qemu-devel@nongnu.org; Wed, 21 Jul 2021 12:00:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:29770) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m6Eda-0001jG-4u for qemu-devel@nongnu.org; Wed, 21 Jul 2021 12:00:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626883196; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=j7zH2LDBctMOCpWMDNHTrhHf2CPCNJnl53ztOEz1gow=; b=i61144ABw93kT23sjznNDX0ltU6FGnlSGfDoRN9gxiQ1tVvp+dD3YwXPx5VjUe3m+BqHnP JjcPgGbRiQfCJlbZBbtiRRbWxs/AIyRvQy26l8tThjbE64TkO8auZEzfjdv9biEjtZkKS1 qbvAsEB5BncUAe4igBPFjJkPeLxzUAY= 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-354-moe5dbhpN5e0WHb1uVmc1Q-1; Wed, 21 Jul 2021 11:59:51 -0400 X-MC-Unique: moe5dbhpN5e0WHb1uVmc1Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A33DD10919BF; Wed, 21 Jul 2021 15:57:55 +0000 (UTC) Received: from redhat.com (ovpn-113-72.ams2.redhat.com [10.36.113.72]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 614977E464; Wed, 21 Jul 2021 15:57:50 +0000 (UTC) Date: Wed, 21 Jul 2021 16:57:47 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Subject: Re: [PATCH 2/5] migration: Shutdown src in await_return_path_close_on_source() Message-ID: References: <20210721012134.792845-1-peterx@redhat.com> <20210721012134.792845-3-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.459, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , Lukas Straub , Juan Quintela , qemu-devel@nongnu.org, Peter Xu , Leonardo Bras Soares Passos Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 21, 2021 at 10:55:00AM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (peterx@redhat.com) wrote: > > We have a logic in await_return_path_close_on_source() that we will explicitly > > shutdown the socket when migration encounters errors. However it could be racy > > because from_dst_file could have been reset right after checking it but before > > passing it to qemu_file_shutdown() by the rp_thread. > > > > Fix it by shutdown() on the src file instead. Since they must be a pair of > > qemu files, shutdown on either of them will work the same. > > > > Since at it, drop the check for from_dst_file directly, which makes the > > behavior even more predictable. > > So while the existing code maybe racy, I'm not sure that this change > keeps the semantics; the channel may well have dup()'d the fd's for the > two directions, and I'm not convinced that a shutdown() on one will > necessarily impact the other; and if the shutdown doesn't happen the > rp_thread might not exit, and we might block on the koin. My understanding is that 'shutdown' operation affects the state of the socket connection. An FD is merely the way a socket is exposed to userspace. Thus if you have multiple FDs all pointing to the same underlying socket (thanks to dup()), then I expect that the effects of 'shutdown' will apply equally to all of the FD copies. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|