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 8F441C48291 for ; Mon, 5 Feb 2024 06:21:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rWsLm-0002TR-2h; Mon, 05 Feb 2024 01:21:02 -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 1rWsLk-0002St-18 for qemu-devel@nongnu.org; Mon, 05 Feb 2024 01:21:00 -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 1rWsLi-0006hE-1Q for qemu-devel@nongnu.org; Mon, 05 Feb 2024 01:20:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707114056; h=from:from: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=1FTy5zDdcqxx35mBArcxs91JvRr9KqrOsCMKH3wY1SM=; b=DT1BV5CvAJvoTgDcpgAYsLeW7u9kMULWt5TJye+6vaSa++YWJ978gAXqP7EbSLslGxkIZP LmMAbHr3LXEjYxxIQe8CwGXEsUy360Sir19EgENvjOoSn/ookEd/3YUAsdOVznkPLFSTkQ +OvkpduacE+8KGcxUd/f9cQ4/1oRd/s= Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-153-te6JpIOWOgqbkeYA_JB1uA-1; Mon, 05 Feb 2024 01:20:54 -0500 X-MC-Unique: te6JpIOWOgqbkeYA_JB1uA-1 Received: by mail-pl1-f199.google.com with SMTP id d9443c01a7336-1d95551c141so1690045ad.0 for ; Sun, 04 Feb 2024 22:20:54 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707114053; x=1707718853; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=1FTy5zDdcqxx35mBArcxs91JvRr9KqrOsCMKH3wY1SM=; b=J2Vzd31Djx7425H7B3RWpCIYhj4tfE08+u/HSbL9HK/bDS+wHlxmsomVXtMhoEw88c Om1jq0Y91EX7Sr2PARLF2N6AeT/vO2T++TWRpUgtdAij+1mNP1THSDZ3k8bbl4Oce2Zd 0QqRywGqyzHsVI+m4OsicDkb2mF6PT3IAgzNOgi3/0+FwRMcug3AbkDgFTM906fNZdXc dcuqx6yu7l6WFZW/RbqtmfNRso1E1MSFdQ2eClzsN+zC8aU+Qp4bsj/V58fRwhFKBFoE 659uQncPKVETMWg3+dYSW78WfTav7le6RLkPttbEnYcaG9ZIlo4DlFpCroE2z8axyIc/ HXlA== X-Gm-Message-State: AOJu0Yzs3ElpTftDJdMlER3XMLB2ZAaM/uAHTYngRdRQXqd50UORHbWF SpQbHIq3veWYCO9rKUVYVpbfVcE6F+S1Lso5L1+JS80qXQJeyKUZ97Kwh83Ga2HAP+nAMSfRxDl y6w3yAVpR9HsXKHkHryYfscAXakvv5GFUbitvN+EVDaRsw05d1J52 X-Received: by 2002:a17:902:d502:b0:1d9:a825:19d1 with SMTP id b2-20020a170902d50200b001d9a82519d1mr3152318plg.0.1707114053132; Sun, 04 Feb 2024 22:20:53 -0800 (PST) X-Google-Smtp-Source: AGHT+IEq00m5B6dL3B3u7J4wp2wxV53KfmjjFhaF6lArPDdnr7XB/5PgVxualAqkEm+hF3d3w/S2Ww== X-Received: by 2002:a17:902:d502:b0:1d9:a825:19d1 with SMTP id b2-20020a170902d50200b001d9a82519d1mr3152309plg.0.1707114052701; Sun, 04 Feb 2024 22:20:52 -0800 (PST) X-Forwarded-Encrypted: i=0; AJvYcCWTA6jQ7pNUBXhi2rXL3iRQddS4fMYjSKWRotQqDy8u/jttvbAuzuJmZHSkX3JzzGwwl8ZXh1yImGw4diQo76Q3SMw= Received: from x1n ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id mm4-20020a1709030a0400b001d8dbb867b1sm5512329plb.179.2024.02.04.22.20.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 04 Feb 2024 22:20:52 -0800 (PST) Date: Mon, 5 Feb 2024 14:20:43 +0800 From: Peter Xu To: Fabiano Rosas Cc: qemu-devel@nongnu.org, Avihai Horon Subject: Re: [PATCH 5/5] migration/multifd: Add a synchronization point for channel creation Message-ID: References: <20240202191128.1901-1-farosas@suse.de> <20240202191128.1901-6-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240202191128.1901-6-farosas@suse.de> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@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: , 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 04:11:28PM -0300, Fabiano Rosas wrote: > It is possible that one of the multifd channels fails to be created at > multifd_new_send_channel_async() while the rest of the channel > creation tasks are still in flight. > > This could lead to multifd_save_cleanup() executing the > qemu_thread_join() loop too early and not waiting for the threads > which haven't been created yet, leading to the freeing of resources > that the newly created threads will try to access and crash. > > Add a synchronization point after which there will be no attempts at > thread creation and therefore calling multifd_save_cleanup() past that > point will ensure it properly waits for the threads. > > A note about performance: Prior to this patch, if a channel took too > long to be established, other channels could finish connecting first > and already start taking load. Now we're bounded by the > slowest-connecting channel. Yes, I think this should (hopefully!) be fine. > > Signed-off-by: Fabiano Rosas > --- > migration/multifd.c | 67 +++++++++++++++++++++++++-------------------- > 1 file changed, 37 insertions(+), 30 deletions(-) > > diff --git a/migration/multifd.c b/migration/multifd.c > index 1851206352..888ac8b05d 100644 > --- a/migration/multifd.c > +++ b/migration/multifd.c > @@ -360,6 +360,11 @@ struct { > MultiFDPages_t *pages; > /* global number of generated multifd packets */ > uint64_t packet_num; > + /* > + * Synchronization point past which no more channels will be > + * created. > + */ > + QemuSemaphore channels_created; > /* send channels ready */ > QemuSemaphore channels_ready; > /* > @@ -561,6 +566,7 @@ void multifd_save_cleanup(void) > error_free(local_err); > } > } > + qemu_sem_destroy(&multifd_send_state->channels_created); > qemu_sem_destroy(&multifd_send_state->channels_ready); > g_free(multifd_send_state->params); > multifd_send_state->params = NULL; > @@ -787,13 +793,6 @@ static void multifd_tls_outgoing_handshake(QIOTask *task, > trace_multifd_tls_outgoing_handshake_error(ioc, error_get_pretty(err)); > > migrate_set_error(migrate_get_current(), err); > - /* > - * Error happen, mark multifd_send_thread status as 'quit' although it > - * is not created, and then tell who pay attention to me. > - */ > - p->quit = true; > - qemu_sem_post(&multifd_send_state->channels_ready); > - qemu_sem_post(&p->sem_sync); > error_free(err); > } > > @@ -862,39 +861,37 @@ static bool multifd_channel_connect(MultiFDSendParams *p, > return true; > } > > -static void multifd_new_send_channel_cleanup(MultiFDSendParams *p, > - QIOChannel *ioc, Error *err) > -{ > - migrate_set_error(migrate_get_current(), err); > - /* Error happen, we need to tell who pay attention to me */ > - qemu_sem_post(&multifd_send_state->channels_ready); > - qemu_sem_post(&p->sem_sync); > - /* > - * Although multifd_send_thread is not created, but main migration > - * thread need to judge whether it is running, so we need to mark > - * its status. > - */ > - p->quit = true; > - object_unref(OBJECT(ioc)); > - error_free(err); > -} > - > static void multifd_new_send_channel_async(QIOTask *task, gpointer opaque) > { > MultiFDSendParams *p = opaque; > QIOChannel *ioc = QIO_CHANNEL(qio_task_get_source(task)); > Error *local_err = NULL; > + bool ret; > > trace_multifd_new_send_channel_async(p->id); > - if (!qio_task_propagate_error(task, &local_err)) { > - qio_channel_set_delay(ioc, false); > - if (multifd_channel_connect(p, ioc, &local_err)) { > - return; > - } > + > + if (qio_task_propagate_error(task, &local_err)) { > + ret = false; > + goto out; > + } > + > + qio_channel_set_delay(ioc, false); > + ret = multifd_channel_connect(p, ioc, &local_err); > + > +out: > + /* > + * Here we're not interested whether creation succeeded, only that > + * it happened at all. > + */ > + qemu_sem_post(&multifd_send_state->channels_created); > + if (ret) { > + return; > } > > trace_multifd_new_send_channel_async_error(p->id, local_err); > - multifd_new_send_channel_cleanup(p, ioc, local_err); > + migrate_set_error(migrate_get_current(), local_err); > + object_unref(OBJECT(ioc)); > + error_free(local_err); > } > > static void multifd_new_send_channel_create(gpointer opaque) > @@ -918,6 +915,7 @@ bool multifd_save_setup(void) > multifd_send_state = g_malloc0(sizeof(*multifd_send_state)); > multifd_send_state->params = g_new0(MultiFDSendParams, thread_count); > multifd_send_state->pages = multifd_pages_init(page_count); > + qemu_sem_init(&multifd_send_state->channels_created, 0); > qemu_sem_init(&multifd_send_state->channels_ready, 0); > qatomic_set(&multifd_send_state->exiting, 0); > multifd_send_state->ops = multifd_ops[migrate_multifd_compression()]; > @@ -953,6 +951,15 @@ bool multifd_save_setup(void) > multifd_new_send_channel_create(p); > } > > + /* > + * Wait until channel creation has started for all channels. The > + * creation can still fail, but no more channels will be created > + * past this point. > + */ Let me double check with you here on the TLS use case. IIUC we still can have more channels to be created if TLS is enabled: we notify the sem as long as the handshake thread is created, then the handshake thread can further create the tls-armed iochannel? However I think I get your point, and that is fine, because if that is the case, even though this loop can complete before tls further creates the final channel, we'll still see tls_thread_created==true and join() that tls thread first, then further we'll join() the next multifd thread even if a new one will pop up, or if it failed then nothing to join besides the tls thread. I'm not sure whether Avihai has any input, I think this can be a good idea indeed. there's a dependency chain on the ordering if my above undertanding is correct; we may want to document this somewhere, perhaps right here on the chaining of threads and how we handle that? This may not allow a concurrent migrate_cancel to respond, but I assume this is good enough; the migrate_cancel request is indeed at least so far something I made up, but not a request from anyone. We can leave that for later and fix the race / crash first. This seems to be a complete fix from that regard. > + for (i = 0; i < thread_count; i++) { > + qemu_sem_wait(&multifd_send_state->channels_created); > + } > + > for (i = 0; i < thread_count; i++) { > MultiFDSendParams *p = &multifd_send_state->params[i]; > > -- > 2.35.3 > One other note is I think this will also deserve a cc: stable? But then it'll mean all patch 3/4 will also need to copy stable to make Michael's life easier. Let's also copy Dan when repost; after all he more or less owns the TLS part. Thanks! -- Peter Xu