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 1FC6AC4332F for ; Wed, 1 Dec 2021 14:13:56 +0000 (UTC) Received: from localhost ([::1]:49322 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1msQMt-0003Y6-1m for qemu-devel@archiver.kernel.org; Wed, 01 Dec 2021 09:13:55 -0500 Received: from eggs.gnu.org ([209.51.188.92]:34594) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1msQJk-0001KU-Rv for qemu-devel@nongnu.org; Wed, 01 Dec 2021 09:10:40 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:24539) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1msQJe-0006hJ-EH for qemu-devel@nongnu.org; Wed, 01 Dec 2021 09:10:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1638367832; 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=dPQBWSiFd4l3XEYqrXoE+y2FnYokcyZK/wJNmct1g+A=; b=cPNJR6ekiG1bymmKICTdjRBeWWuRhjAUNmpwgZrKzCoVQIsSZujEm+ydp0v5fjHYednH/W lrJnDcpqIf+YRzXVf7vFvlrDMfibCBTS9w73OkWvOq9DLLXKndyomVa+yMGOCeISIjDTcq kClJi9qi+BeQODIekZQZyQepbXdeeYY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-83-azcwhgZ-OYC3FShIBPnkpQ-1; Wed, 01 Dec 2021 09:10:27 -0500 X-MC-Unique: azcwhgZ-OYC3FShIBPnkpQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3C917100CC94; Wed, 1 Dec 2021 14:10:19 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.152]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 47C9950239; Wed, 1 Dec 2021 14:09:59 +0000 (UTC) Date: Wed, 1 Dec 2021 14:09:56 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Li Zhang Subject: Re: [PATCH 1/2] multifd: use qemu_sem_timedwait in multifd_recv_thread to avoid waiting forever Message-ID: References: <20211126153154.25424-1-lizhang@suse.de> <20211126153154.25424-2-lizhang@suse.de> <50dbb2b9-152e-f97a-d82e-0b6613e54085@suse.de> <9b20d47c-8b4e-b1b2-c0b9-1ec82dc775ff@suse.de> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.3 (2021-09-10) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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 Content-Transfer-Encoding: 8bit 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: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.716, 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_H3=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: qemu-devel@nongnu.org, cfontana@suse.de, "Dr. David Alan Gilbert" , quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Dec 01, 2021 at 02:42:04PM +0100, Li Zhang wrote: > > On 12/1/21 1:22 PM, Daniel P. Berrangé wrote: > > On Wed, Dec 01, 2021 at 01:11:13PM +0100, Li Zhang wrote: > > > On 11/29/21 3:50 PM, Dr. David Alan Gilbert wrote: > > > > * Li Zhang (lizhang@suse.de) wrote: > > > > > On 11/29/21 12:20 PM, Dr. David Alan Gilbert wrote: > > > > > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > > > > > > On Fri, Nov 26, 2021 at 04:31:53PM +0100, Li Zhang wrote: > > > > > > > > When doing live migration with multifd channels 8, 16 or larger number, > > > > > > > > the guest hangs in the presence of the network errors such as missing TCP ACKs. > > > > > > > > > > > > > > > > At sender's side: > > > > > > > > The main thread is blocked on qemu_thread_join, migration_fd_cleanup > > > > > > > > is called because one thread fails on qio_channel_write_all when > > > > > > > > the network problem happens and other send threads are blocked on sendmsg. > > > > > > > > They could not be terminated. So the main thread is blocked on qemu_thread_join > > > > > > > > to wait for the threads terminated. > > > > > > > Isn't the right answer here to ensure we've called 'shutdown' on > > > > > > > all the FDs, so that the threads get kicked out of sendmsg, before > > > > > > > trying to join the thread ? > > > > > > I agree a timeout is wrong here; there is no way to get a good timeout > > > > > > value. > > > > > > However, I'm a bit confused - we should be able to try a shutdown on the > > > > > > receive side using the 'yank' command. - that's what it's there for; Li > > > > > > does this solve your problem? > > > > > No, I tried to register 'yank' on the receive side, the receive threads are > > > > > still waiting there. > > > > > > > > > > It seems that on send side, 'yank' doesn't work either when the send threads > > > > > are blocked. > > > > > > > > > > This may be not the case to call yank. I am not quite sure about it. > > > > We need to fix that; 'yank' should be able to recover from any network > > > > issue. If it's not working we need to understand why. > > > Hi Dr. David, > > > > > > On the receive side, I register 'yank' and it is called. But it is just to > > > shut down the channels, > > > > > > it couldn't fix the problem of the receive threads which are waiting for the > > > semaphore. > > > > > > So the receive threads are still waiting there. > > > > > > On the send side,  the main process is blocked on qemu_thread_join(), when I > > > tried the 'yank' > > > > > > command with QMP,  it is not handled. So the QMP doesn't work and yank > > > doesn't work. > > IOW, there is a bug in QEMU on the send side. It should not be calling > > qemu_thread_join() from the main thread, unless it is extremely > > confident that the thread in question has already finished. > > > > You seem to be showing that the thread(s) are still running, so we > > need to understand why that is the case, and why the main thread > > still decided to try to join these threads which haven't finished. > > Some threads are running. But there is one thread fails to > qio_channel_write_all. > > In migration_thread(), it detects an error here: > >    thr_error = migration_detect_error(s); >         if (thr_error == MIG_THR_ERR_FATAL) { >             /* Stop migration */ >             break; > > It will stop migration and cleanup. Those threads which are still running need to be made to terminate before trying to join them A quick glance at multifd_send_terminate_threads() makes me suspect multifd shutdown is not reliable. It is merely setting some boolean flags and posting to a semaphore. It is doing nothing to shutdown the socket associated with each thread, so the threads can still be waiting in an I/O call. IMHO multifd_send_terminate_threads needs to call qio_chanel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH) 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 :|