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 X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46418C433E6 for ; Fri, 5 Feb 2021 16:03:39 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 6E60264F30 for ; Fri, 5 Feb 2021 16:03:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E60264F30 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:45766 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l83a5-0007oJ-5h for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 11:03:37 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:32772) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l83Yk-000731-Ej for qemu-devel@nongnu.org; Fri, 05 Feb 2021 11:02:14 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:40901) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l83Yg-00039K-R9 for qemu-devel@nongnu.org; Fri, 05 Feb 2021 11:02:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612540928; 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=j7XLtWGYu/YcuJLZotFQJLJ0vVj/BEcBcg5XSbN7LuI=; b=CtzXbJ8ypZJ32H6e5YbCKZy12kb3RiLLx9wwqR1t/qtNb4tvplZUp0x6QiZOadR71w0ua2 AVTZFeSgVBV9poU25DWHQTGo0Cnr2+nH0h9r64vzqO3QiANx9c33Gol6M5LVTQ6GBZbx5B nvWDHJTmMXTxESS1wk0QjUoIM8RUVoA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-2-kO0qzTMtPB6QzZdZP0y5QQ-1; Fri, 05 Feb 2021 11:02:02 -0500 X-MC-Unique: kO0qzTMtPB6QzZdZP0y5QQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4709B8710EE; Fri, 5 Feb 2021 16:02:01 +0000 (UTC) Received: from merkur.fritz.box (ovpn-114-240.ams2.redhat.com [10.36.114.240]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B3E2F5C257; Fri, 5 Feb 2021 16:01:59 +0000 (UTC) Date: Fri, 5 Feb 2021 17:01:58 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v2 29/36] blockdev: qmp_x_blockdev_reopen: acquire all contexts Message-ID: <20210205160158.GE7072@merkur.fritz.box> References: <20201127144522.29991-1-vsementsov@virtuozzo.com> <20201127144522.29991-30-vsementsov@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <20201127144522.29991-30-vsementsov@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@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=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.352, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-block@nongnu.org, armbru@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 27.11.2020 um 15:45 hat Vladimir Sementsov-Ogievskiy geschrieben: > During reopen we may add backing bs from other aio context, which may > lead to changing original context of top bs. > > We are going to move graph modification to prepare stage. So, it will > be possible that bdrv_flush() in bdrv_reopen_prepare called on bs in > non-original aio context, which we didn't aquire which leads to crash. > > More correct would be to acquire all aio context we are going to work > with. And the simplest ways is to just acquire all of them. It may be > optimized later if needed. > > Signed-off-by: Vladimir Sementsov-Ogievskiy I'm afraid it's not as easy. Holding the lock of more than one AioContext is always a bit risky with respect to deadlocks. For example, changing the AioContext of a node with bdrv_set_aio_context_ignore() has explicit rules that are now violated: * The caller must own the AioContext lock for the old AioContext of bs, but it * must not own the AioContext lock for new_context (unless new_context is the * same as the current context of bs). Draining while holding all AioContext locks is suspicious, too. I think I have seen deadlocks before, which is why bdrv_drain_all_*() are careful to only ever lock a single AioContext at a time. Kevin