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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 9C2B8C4828D for ; Mon, 5 Feb 2024 10:33:02 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rWwHM-0006cC-6K; Mon, 05 Feb 2024 05:32:44 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rWwHK-0006bx-DU for qemu-devel@nongnu.org; Mon, 05 Feb 2024 05:32:42 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rWwHI-0005w6-Q4 for qemu-devel@nongnu.org; Mon, 05 Feb 2024 05:32:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707129160; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FRcN3IQhhXp+o6SmZxXbDJdiHWjY3cCmRN08jogxgVQ=; b=Bagyzz7kPZP6MPhWM7avo9iPCBhDJF5X/6invE9Z3YZnNR44PuUD8pMEmRHfIbd0I2Bfdf ieOdUQjC+Bv8S8IWuB4LxwuCM9NwafWlhazX7BJQuMBnfUXu6uK/Rh7dxjLJpqJkYNqyN+ rxpotFgolPDbUZMhmchXt+BppVjEddU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-189-GhLSQENyPqiXyumwBG_itQ-1; Mon, 05 Feb 2024 05:32:36 -0500 X-MC-Unique: GhLSQENyPqiXyumwBG_itQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5C004101A526; Mon, 5 Feb 2024 10:32:36 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.69]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 863222166B31; Mon, 5 Feb 2024 10:32:35 +0000 (UTC) Date: Mon, 5 Feb 2024 10:32:33 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: =?utf-8?Q?C=C3=A9dric?= Le Goater , qemu-devel@nongnu.org, Fabiano Rosas Subject: Re: [PATCH 0/2] migration: Fix return-path thread exit Message-ID: References: <20240201184853.890471-1-clg@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.361, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Feb 02, 2024 at 05:53:39PM +0800, Peter Xu wrote: > On Thu, Feb 01, 2024 at 07:48:51PM +0100, Cédric Le Goater wrote: > > Hello, > > Hi, Cédric, > > Thanks for the patches. > > > > > Today, close_return_path_on_source() can perform a shutdown to exit > > the return-path thread if an error occured. However, migrate_fd_cleanup() > > does cleanups too early and the shutdown in close_return_path_on_source() > > fails, leaving the source and destination waiting for an event to occur. > > > > This little series tries to fix that. Comments welcome ! > > One thing I do agree is that relying on qemu_file_get_error(to_dst_file) in > close_return_path_on_source() is weird: IMHO we have better way to detect > "whether the migration has error" now, which is migrate_has_error(). > > For this specific issue, I think one long standing issue that might be > relevant is we have two QEMUFile (from_dst_file, to_dst_file) that share > the same QIOChannel now. Logically the two QEMUFile should be able to be > managed separately, say, close() of to_dst_file shouldn't affect the other. > > However I don't think it's the case now, as qemu_fclose(to_dst_file) will > do qio_channel_close() already, which means there will be a side effect to > the other QEMUFile that its backing IOC is already closed. > > Is this the issue we're facing? IOW, the close() of to_dst_file will not > properly kick the other thread who is blocked at reading from_dst_file, > while the shutdown() will kick it out? > > If so, not sure whether we can somehow relay the real qio_channel_close() > to until the last user releases it? IOW, conditionally close() the channel > in qio_channel_finalize(), if the channel is still open? Would that make > sense? IMHO the problem described above is a result of the design mistake of having 2 separate QEMUFile instances for what is ultimately the same channel. This was a convenient approach to take originally, but it has likely outlived its purpose. In the ideal world IMHO, QEMUFile would not exist at all, and we would have a QIOChannelCached that adds the read/write buffering above the base QIOChannel. That's doable, but bigger than a quick fix. A natural stepping stone to get there though is to move from 2 QEMUFile objs down to 1 QEMUFile, which might be more practical as a quick fix. With 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 :|