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 655B7C636CC for ; Wed, 15 Feb 2023 18:28:43 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pSMVe-0002Vq-Km; Wed, 15 Feb 2023 13:28:02 -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 1pSMVc-0002VM-W9 for qemu-devel@nongnu.org; Wed, 15 Feb 2023 13:28:01 -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 1pSMVa-0001Zt-B3 for qemu-devel@nongnu.org; Wed, 15 Feb 2023 13:28:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1676485676; 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=KpRUkJBqeMdptGMqenj7ncP3Q+Hj+F/RYAH9sRQ2AQw=; b=Itmv4CApHI/oKhlD28DCmL/m+QI38/QZwsYKUYfHkVodaBbzk5zNUunhvTLR8YBni6m4mt hnoksShGG11HoITvK6KEVpayNQXuQ2hoAYY3x0WSLixm0L0EISdYub/i5Dmfb/DRPP6kU4 RAOA4bq5u6a6+4g0ESUxvg2npXlBN0k= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-443-qvQSc9uaPt-6cI4GN1q4qQ-1; Wed, 15 Feb 2023 13:27:55 -0500 X-MC-Unique: qvQSc9uaPt-6cI4GN1q4qQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 05DEA85CBE0; Wed, 15 Feb 2023 18:27:55 +0000 (UTC) Received: from redhat.com (unknown [10.2.16.217]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 14FF32026D4B; Wed, 15 Feb 2023 18:27:53 +0000 (UTC) Date: Wed, 15 Feb 2023 12:27:52 -0600 From: Eric Blake To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, "Michael S. Tsirkin" , Paolo Bonzini , David Hildenbrand , Peter Xu , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Fam Zheng , Qing Wang Subject: Re: [PATCH v2 3/3] virtio-scsi: reset SCSI devices from main loop thread Message-ID: <20230215182752.4s4pgs3gcor6try3@redhat.com> References: <20230210143238.524357-1-stefanha@redhat.com> <20230210143238.524357-4-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230210143238.524357-4-stefanha@redhat.com> User-Agent: NeoMutt/20220429 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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 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 10, 2023 at 09:32:38AM -0500, Stefan Hajnoczi wrote: > When an IOThread is configured, the ctrl virtqueue is processed in the > IOThread. TMFs that reset SCSI devices are currently called directly > from the IOThread and trigger an assertion failure in blk_drain(): > > ../block/block-backend.c:1780: void blk_drain(BlockBackend *): Assertion `qemu_in_main_thread()' failed. > > The blk_drain() function is not designed to be called from an IOThread > because it needs the Big QEMU Lock (BQL). > > This patch defers TMFs that reset SCSI devices to a Bottom Half (BH) > that runs in the main loop thread under the BQL. This way it's safe to > call blk_drain() and the assertion failure is avoided. > > Introduce s->tmf_bh_list for tracking TMF requests that have been > deferred to the BH. When the BH runs it will grab the entire list and > process all requests. Care must be taken to clear the list when the > virtio-scsi device is reset or unrealized. Otherwise deferred TMF > requests could execute later and lead to use-after-free or other > undefined behavior. > > The s->resetting counter that's used by TMFs that reset SCSI devices is > accessed from multiple threads. This patch makes that explicit by using > atomic accessor functions. With this patch applied the counter is only > modified by the main loop thread under the BQL but can be read by any > thread. > > Reported-by: Qing Wang > Cc: Paolo Bonzini > Signed-off-by: Stefan Hajnoczi > --- > include/hw/virtio/virtio-scsi.h | 11 ++- > hw/scsi/virtio-scsi.c | 169 +++++++++++++++++++++++++------- > 2 files changed, 143 insertions(+), 37 deletions(-) This one is trickier than the first two, so if you want a second reviewer, I understand. That said, although the number of lines of code grows, the code motion into separate handlers was fairly easy to follow, and the logic for why they must be in a separate BH context is correct. Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org