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 451D5C433F5 for ; Wed, 23 Feb 2022 10:34:10 +0000 (UTC) Received: from localhost ([::1]:46656 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nMoyH-0001UH-2r for qemu-devel@archiver.kernel.org; Wed, 23 Feb 2022 05:34:09 -0500 Received: from eggs.gnu.org ([209.51.188.92]:58752) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nMoJx-00033H-9C for qemu-devel@nongnu.org; Wed, 23 Feb 2022 04:52:34 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49713) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nMoJu-0000iv-Ps for qemu-devel@nongnu.org; Wed, 23 Feb 2022 04:52:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645609937; 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=4oM+EUp0DOr9XsFqdcNvNWhJ+ca86V0sgRQ5pZx06go=; b=BDlkCoPKH99IRU7ZpTyYUH3Z8ml/39rkucuRZFr5UdfOASZZ2Pm2rVVFQ+M6jVc3vrFUDM Jcqe0FolQOMxXfwdFkCKBEi1HisO8qFMjp/N4fU/it2w6Pv/qxweftdBndJlmorUrWgwE8 J5vDvgBHDBzqUsg1mkvE+eOD850sdxI= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-636-2-VZZQZ8ND6zKIjWZJ8BNA-1; Wed, 23 Feb 2022 04:52:16 -0500 X-MC-Unique: 2-VZZQZ8ND6zKIjWZJ8BNA-1 Received: by mail-wr1-f69.google.com with SMTP id c16-20020adfa310000000b001ed9cd8f4c7so1292590wrb.6 for ; Wed, 23 Feb 2022 01:52:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=4oM+EUp0DOr9XsFqdcNvNWhJ+ca86V0sgRQ5pZx06go=; b=wSDPd4TfAaSHLbsEBX37pDYYQVHLXLH7uvtOGVF3/hzJq2DM8zkTEmRMEgaA1z1UDN KzWUB4Af0Is7VqU7JoW043c+XA8N1HaEF3QJ6xfubRQgVqt71a0rYeMdYO3FFAJ9e5Di eL66Q/A/yNxCaGhbjJoO/TSnTuE7KGEQY7qrMBMrxYC9Sva+7Mu0kVAhWDX58YNqq9fZ /b1gIySLnKtyUPuILR0s9zSrilS1xjBsuFYVv4QdKlht/e+MP8F42T5FS4RCCOPKjJtY dqKKmlm7nlnjVnsqwrUu8xQkKGl7hnRvw23bWT18nIwvPkgUSZnZhpMYjl7gvkftVOyo NECA== X-Gm-Message-State: AOAM5308yUz/ZLcgC/KWAzGKZYVlVdXQUFwUr5ENOFk7rl7ejmLMn9be 15hCtCalCkisnOcwe44YHR1x0dYqVKp3ppWIfjvzpO3FWHJjlDbmOj4a6cEs23nQhx+v7Q5gBTs oj2+MNvpKS9pd3wM= X-Received: by 2002:adf:e951:0:b0:1e6:85e6:65d9 with SMTP id m17-20020adfe951000000b001e685e665d9mr22039485wrn.412.1645609931325; Wed, 23 Feb 2022 01:52:11 -0800 (PST) X-Google-Smtp-Source: ABdhPJwgew4uIT5tvjLgJrNahSu7Nd00aYQyjOJfrXrH5NWeDDVGTsC29AADbdw9CsE/cE+D9HVMLg== X-Received: by 2002:adf:e951:0:b0:1e6:85e6:65d9 with SMTP id m17-20020adfe951000000b001e685e665d9mr22039466wrn.412.1645609930993; Wed, 23 Feb 2022 01:52:10 -0800 (PST) Received: from work-vm (cpc109025-salf6-2-0-cust480.10-2.cable.virginm.net. [82.30.61.225]) by smtp.gmail.com with ESMTPSA id q2sm53937391wrw.14.2022.02.23.01.52.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Feb 2022 01:52:10 -0800 (PST) Date: Wed, 23 Feb 2022 09:52:08 +0000 From: "Dr. David Alan Gilbert" To: Peter Xu Subject: Re: [PATCH 19/20] migration: Postcopy recover with preempt enabled Message-ID: References: <20220216062809.57179-1-peterx@redhat.com> <20220216062809.57179-20-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, 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_H5=0.001, RCVD_IN_MSPIKE_WL=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: , Cc: Leonardo Bras Soares Passos , qemu-devel@nongnu.org, Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) wrote: > On Tue, Feb 22, 2022 at 11:32:10AM +0000, Dr. David Alan Gilbert wrote: > > * Peter Xu (peterx@redhat.com) wrote: > > > To allow postcopy recovery, the ram fast load (preempt-only) dest QEMU thread > > > needs similar handling on fault tolerance. When ram_load_postcopy() fails, > > > instead of stopping the thread it halts with a semaphore, preparing to be > > > kicked again when recovery is detected. > > > > > > A mutex is introduced to make sure there's no concurrent operation upon the > > > socket. To make it simple, the fast ram load thread will take the mutex during > > > its whole procedure, and only release it if it's paused. The fast-path socket > > > will be properly released by the main loading thread safely when there's > > > network failures during postcopy with that mutex held. > > > > I *think* this is mostly OK; but I worry I don't understand all the > > cases; e.g. > > a) If the postcopy channel errors first > > b) If the main channel errors first > > Ah right, I don't think I handled all the cases. Sorry. > > We always check the main channel, but if the postcopy channel got faulted, > we may not fall into paused mode as expected. > > I'll fix that up. Thanks. > > > > Can you add some docs to walk through those and explain the locking ? > > Sure. > > The sem is mentioned in the last sentence of paragraph 1, where it's purely > used for a way to yield the fast ram load thread so that when something > wrong happens it can sleep on that semaphore. Then when we recover we'll > post to the semaphore to kick it up. We used it like that in many places, > e.g. postcopy_pause_sem_dst to yield the main load thread. > > The 2nd paragraph above was for explaining why we need the mutex; it's > basically the same as rp_mutex protecting to_src_file, so that we won't > accidentally close() the qemufile during some other thread using it. So > the fast ram load thread needs to take that new mutex for mostly the whole > lifecycle of itself (because it's loading from that qemufile), meanwhile > only drop the mutex when it prepares to sleep. Then the main load thread > can recycle the postcopy channel using qemu_fclose() safely. Yes, that feels like it needs to go in the code somewhere. > [...] > > > > @@ -3466,6 +3468,17 @@ static MigThrError postcopy_pause(MigrationState *s) > > > qemu_file_shutdown(file); > > > qemu_fclose(file); > > > > > > + /* > > > + * Do the same to postcopy fast path socket too if there is. No > > > + * locking needed because no racer as long as we do this before setting > > > + * status to paused. > > > + */ > > > + if (s->postcopy_qemufile_src) { > > > + migration_ioc_unregister_yank_from_file(s->postcopy_qemufile_src); > > > > Shouldn't this do a qemu_file_shutdown on here first? > > Yes I probably should. > > With all above, I plan to squash below changes into this patch: > > ---8<--- > diff --git a/migration/migration.c b/migration/migration.c > index c68a281406..69778cab23 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -3475,6 +3475,7 @@ static MigThrError postcopy_pause(MigrationState *s) > */ > if (s->postcopy_qemufile_src) { > migration_ioc_unregister_yank_from_file(s->postcopy_qemufile_src); > + qemu_file_shutdown(s->postcopy_qemufile_src); > qemu_fclose(s->postcopy_qemufile_src); > s->postcopy_qemufile_src = NULL; > } > @@ -3534,8 +3535,13 @@ static MigThrError migration_detect_error(MigrationState *s) > return MIG_THR_ERR_FATAL; > } > > - /* Try to detect any file errors */ > - ret = qemu_file_get_error_obj(s->to_dst_file, &local_error); > + /* > + * Try to detect any file errors. Note that postcopy_qemufile_src will > + * be NULL when postcopy preempt is not enabled. > + */ > + ret = qemu_file_get_error_obj_any(s->to_dst_file, > + s->postcopy_qemufile_src, > + &local_error); > if (!ret) { > /* Everything is fine */ > assert(!local_error); > diff --git a/migration/qemu-file.c b/migration/qemu-file.c > index 1479cddad9..397652f0ba 100644 > --- a/migration/qemu-file.c > +++ b/migration/qemu-file.c > @@ -139,6 +139,33 @@ int qemu_file_get_error_obj(QEMUFile *f, Error **errp) > return f->last_error; > } > > +/* > + * Get last error for either stream f1 or f2 with optional Error*. > + * The error returned (non-zero) can be either from f1 or f2. > + * > + * If any of the qemufile* is NULL, then skip the check on that file. > + * > + * When there is no error on both qemufile, zero is returned. > + */ > +int qemu_file_get_error_obj_any(QEMUFile *f1, QEMUFile *f2, Error **errp) > +{ > + int ret = 0; > + > + if (f1) { > + ret = qemu_file_get_error_obj(f1, errp); > + /* If there's already error detected, return */ > + if (ret) { > + return ret; > + } > + } > + > + if (f2) { > + ret = qemu_file_get_error_obj(f2, errp); > + } > + > + return ret; > +} > + > /* > * Set the last error for stream f with optional Error* > */ > diff --git a/migration/qemu-file.h b/migration/qemu-file.h > index 3f36d4dc8c..2564e5e1c7 100644 > --- a/migration/qemu-file.h > +++ b/migration/qemu-file.h > @@ -156,6 +156,7 @@ void qemu_file_update_transfer(QEMUFile *f, int64_t len); > void qemu_file_set_rate_limit(QEMUFile *f, int64_t new_rate); > int64_t qemu_file_get_rate_limit(QEMUFile *f); > int qemu_file_get_error_obj(QEMUFile *f, Error **errp); > +int qemu_file_get_error_obj_any(QEMUFile *f1, QEMUFile *f2, Error **errp); > void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err); > void qemu_file_set_error(QEMUFile *f, int ret); > int qemu_file_shutdown(QEMUFile *f); > diff --git a/migration/savevm.c b/migration/savevm.c > index 2d32340d28..24b69a1008 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -2651,8 +2651,8 @@ retry: > while (true) { > section_type = qemu_get_byte(f); > > - if (qemu_file_get_error(f)) { > - ret = qemu_file_get_error(f); > + ret = qemu_file_get_error_obj_any(f, mis->postcopy_qemufile_dst, NULL); > + if (ret) { > break; > } > ---8<--- > > Does it look sane? Let me know if there's still things missing. Reviewed-by: Dr. David Alan Gilbert > > Thanks! > > -- > Peter Xu > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK