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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 B6181C28CC0 for ; Wed, 29 May 2019 22:13:27 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8CFB62426E for ; Wed, 29 May 2019 22:13:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8CFB62426E 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 ([127.0.0.1]:36153 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hW6p4-0007V0-Ok for qemu-devel@archiver.kernel.org; Wed, 29 May 2019 18:13:26 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49734) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hW6mP-0005Tn-50 for qemu-devel@nongnu.org; Wed, 29 May 2019 18:10:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hW6mO-0000vJ-8H for qemu-devel@nongnu.org; Wed, 29 May 2019 18:10:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41188) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hW6mO-0000v4-2k for qemu-devel@nongnu.org; Wed, 29 May 2019 18:10:40 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6F92F307D849; Wed, 29 May 2019 22:10:39 +0000 (UTC) Received: from localhost.localdomain (ovpn-116-55.ams2.redhat.com [10.36.116.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 246185D9E1; Wed, 29 May 2019 22:10:31 +0000 (UTC) Date: Thu, 30 May 2019 00:10:30 +0200 From: Kevin Wolf To: Paolo Bonzini Message-ID: <20190529221030.GD3471@localhost.localdomain> References: <20190524183638.20745-1-stefanha@redhat.com> <24b93cc5-edb1-a197-14be-e63ac356325d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24b93cc5-edb1-a197-14be-e63ac356325d@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Wed, 29 May 2019 22:10:39 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC v3 0/3] scsi: restart dma after vm change state handlers X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , qemu-devel@nongnu.org, Stefan Hajnoczi , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 24.05.2019 um 20:47 hat Paolo Bonzini geschrieben: > On 24/05/19 20:36, Stefan Hajnoczi wrote: > > v3: > > * Fix s/k->vmstate_change/vdc->vmstate_change/ > > * Still RFC, waiting for customer to confirm this fixes the issue > > v2: > > * Do it properly with a clean API instead of deferring to a BH! > > Thanks for encouraging me to do this, Kevin. > > > > These patches solve a deadlock when the 'cont' command is used and there are > > failed requests on a virtio-scsi device with iothreads. The deadlock itself is > > actually not the thing we need to fix because we should never reach that case > > anyway. Instead we need to make sure DMA restart is only performed after the > > virtio-scsi iothread is re-initialized. > > custom_dma_restart is a bit ugly... Do you think it would make sense to > order the VMStateChange handlers using some kind of enum (with the order > unspecified within the category)? > > We could start with > > VMSTATECHANGE_PRIO_UNKNOWN = 0 (if needed?) > VMSTATECHANGE_PRIO_IOTHREAD = 100 > VMSTATECHANGE_PRIO_DEVICE = 200 > > where higher priorities run first on stop and last on resume. I don't think this is as nice because stopping or resuming a device could involve some async operation (e.g. be delegated to a BH). In this case, a device on a child bus must still wait for the BH (or other async part) to be completed before it can resume its own operation. Basically, a single flat list of global VM state handlers wasn't a good design, because what we actually need in such cases is something hierarchical. Kevin