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 lists1p.gnu.org (lists1p.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 9756CCA5FF1 for ; Wed, 7 Oct 2026 12:01:49 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xEQL8-0005N2-Mx; Wed, 07 Oct 2026 08:01:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xEQKu-0005J5-K1 for qemu-devel@nongnu.org; Wed, 07 Oct 2026 08:01:30 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xEQKs-0000R7-HW for qemu-devel@nongnu.org; Wed, 07 Oct 2026 08:01:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791374485; 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=jDUY8dDIs7xQ4RAtbcMhXoIQSnAy+07tglDTGDuyhlE=; b=Cj175Qkd06ayGawoNjTyEtgbjAS9AwA6sYj2hnrVDWVa+Yh0O7giuGOiC4wf9lMl3UrGnE eogfJhckCNasaAAaabUmprrFrxii7RApzLujNTH199h8cvkQCkcvhVkqXrzwtVg7ridSj+ apXTg2lI6FqAswLmvFAHi6fvQrpZn+E= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-92-fEyQK68XMKKPuyRcsW0B0Q-1; Wed, 7 Oct 2026 12:01:23 +0000 X-MC-Unique: fEyQK68XMKKPuyRcsW0B0Q-1 X-Mimecast-MFC-AGG-ID: fEyQK68XMKKPuyRcsW0B0Q_1791374482 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (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 mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 745CE1801313; Wed, 7 Oct 2026 12:01:21 +0000 (UTC) Received: from redhat.com (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3C3EF766; Wed, 7 Oct 2026 12:01:17 +0000 (UTC) Date: Wed, 7 Oct 2026 07:01:14 -0500 From: Eric Blake To: "Denis V. Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Peter Xu , Fabiano Rosas , Vladimir Sementsov-Ogievskiy , qemu-stable@nongnu.org Subject: Re: [PATCH v2 2/3] migration/block-dirty-bitmap: fix postcopy abort with bitmaps on several nodes Message-ID: References: <20261006170738.453977-1-den@openvz.org> <20261006170738.453977-3-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261006170738.453977-3-den@openvz.org> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 Tue, Oct 06, 2026 at 07:07:37PM +0200, Denis V. Lunev wrote: > From: Denis V. Lunev > > With dirty bitmaps on more than one node, the source switches nodes > during the postcopy bulk phase and sends the node name again. The > destination reads those chunks in the postcopy listen thread, which does > not hold the BQL, and resolves the name through bdrv_lookup_bs(): > > qemu-system-x86_64: ../block.c:6400: bdrv_lookup_bs: Assertion > `qemu_in_main_thread()' failed. > > The bdrv_find_dirty_bitmap() call right after it needs the BQL or the > dirty bitmap lock as well. Taking the BQL there would deadlock: the > listen thread holds s->lock, and dirty_bitmap_mig_before_vm_start() > takes s->lock with the BQL held. > > Every node and bitmap that a non-START chunk refers to was set up by a > START chunk, and those are loaded under the BQL during setup. Record the > node alias there, and resolve all other chunks against s->bitmaps > instead of the block graph. > > Bitmaps on a single node never resend the node name after setup, which > is why migrate-bitmaps-postcopy-test does not catch this. > > Fixes: f791bf7f93f2 ("assertions for block global state API") > Signed-off-by: Denis V. Lunev > Cc: Peter Xu > Cc: Fabiano Rosas > Cc: Eric Blake > Cc: Vladimir Sementsov-Ogievskiy > Cc: qemu-stable@nongnu.org > --- > migration/block-dirty-bitmap.c | 58 +++++++++++++++++++++++++++++++--- > 1 file changed, 54 insertions(+), 4 deletions(-) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org