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 13745C636D6 for ; Thu, 23 Feb 2023 17:22:43 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pVFI2-0005Vb-4v; Thu, 23 Feb 2023 12:21:54 -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 1pVFI0-0005Tm-7e for qemu-devel@nongnu.org; Thu, 23 Feb 2023 12:21:52 -0500 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 1pVFHn-00075b-3k for qemu-devel@nongnu.org; Thu, 23 Feb 2023 12:21:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677172893; 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=HhdNhyG1GZQKNA+2sXcZln6xHVZURhgWJVfXtqkJH5s=; b=EEL3zC4jjx6BoNndFBhMLQlbRy6YJ8AweeuXHrq2TILzVKqjkHMwqQVkKU9c3PkUKquRSp wvIxBzsukdANteDpbMgIkkjHqe+S7nThlW699ZJZ70OMuI/Q+jeQCE4Pa748nOGK6GUcNW iylJk89ZnUocsmRwsNMlUTC4jcGVFWY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-74-BidSgokuMjS7xzaPjDIicQ-1; Thu, 23 Feb 2023 12:21:26 -0500 X-MC-Unique: BidSgokuMjS7xzaPjDIicQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5500B1C02D31; Thu, 23 Feb 2023 17:21:26 +0000 (UTC) Received: from redhat.com (unknown [10.39.192.128]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0B67EC15BA0; Thu, 23 Feb 2023 17:21:22 +0000 (UTC) Date: Thu, 23 Feb 2023 18:21:21 +0100 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" , Peter Xu , Paolo Bonzini , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , David Hildenbrand , Fam Zheng , qemu-block@nongnu.org Subject: Re: [PATCH v3 0/3] virtio-scsi: fix SCSIDevice hot unplug with IOThread Message-ID: References: <20230221212218.1378734-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230221212218.1378734-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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: -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 Am 21.02.2023 um 22:22 hat Stefan Hajnoczi geschrieben: > v3: > - Fix s/see/sees/ typo in Patch 2 commit description [Eric] > - Add call stack to Patch 3 commit description to make it clear how blk_drain() > is invoked [Kevin] > > Unplugging SCSIDevices when virtio-scsi is using an IOThread suffers from race > conditions: > - scsi_device_purge_requests() is called from the IOThread in TMF emulation. > This is unsafe, it should only be called from the BQL. > - SCSIRequest->aiocb is not protected by a lock, so there are races between the > main loop thread and the IOThread when scsi_device_purge_requests() runs in > the main loop thread. > - DMAAIOCB->acb is not protected by a lock, so there are races in the DMA > helpers code when cancelling a request from the main loop thread. > > These fixes solve assertion failures during SCSIDevice hot unplug in > virtio-scsi with IOThread. Expanding the use of the AioContext lock isn't great > since we're in the midst of trying to remove it. However, I think this solution > is appropriate so that stable trees or distros can backport the fix without > depending on QEMU multi-queue block layer refactoring. > > Special thanks to Qing Wang, who helped me iterate these patches because I > couldn't reproduce the assertion failures myself. Thanks, applied to the block branch. Kevin