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 50035C54EBD for ; Fri, 13 Jan 2023 15:45:29 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pGM1p-0001Fr-UV; Fri, 13 Jan 2023 10:31:38 -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 1pGM1j-0001AP-IH for qemu-devel@nongnu.org; Fri, 13 Jan 2023 10:31:32 -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 1pGM1g-0002Ym-Mu for qemu-devel@nongnu.org; Fri, 13 Jan 2023 10:31:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673623885; 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=+lggzdD4XrXIAmz96H3tEcA7mq+f1yz9R3ziDOqcgbc=; b=B5HRg7ktjChGV1tu3XenHaFyABzyET6+jIxwXUvQJLVPcK1BGP9AK5vE5UtMOAOLZQYgao EQguVQzBvrN3PAn5r4TDDeDEhWOI20lGq4o90/DXZvCR7cplSJS91GlorZfENTEdzfHlqA HmbmupqD5ttjuc5YqfhycbWfozwNQ0Y= 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-632-b9G5mTACOTmR6wJTrxHXhA-1; Fri, 13 Jan 2023 10:31:24 -0500 X-MC-Unique: b9G5mTACOTmR6wJTrxHXhA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 27AEF19705B9; Fri, 13 Jan 2023 15:31:24 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2D35153A0; Fri, 13 Jan 2023 15:31:21 +0000 (UTC) Date: Fri, 13 Jan 2023 16:31:20 +0100 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Hanna Reitz , Paolo Bonzini , Fam Zheng , Qing Wang , Emanuele Giuseppe Esposito Subject: Re: [PATCH] block-backend: fix virtio-scsi assertion failure with blk_drain_noref() Message-ID: References: <20230104195633.86143-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230104195633.86143-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 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 04.01.2023 um 20:56 hat Stefan Hajnoczi geschrieben: > scsi_device_purge_requests() is called from I/O code by virtio-scsi TMF > emulation code. It must not call Global State APIs like blk_drain() > because that results in an assertion failure. > > blk_drain() is a Global State API because it uses bdrv_unref(). Actually > ref/unref is unnecessary in device emulation code because the drive= > qdev property holds the reference. Just for the record: We came to the conclusion that this isn't true. We're not doing blk_ref/unref here, but bdrv_ref/unref. The function calls bdrv_drained_end(bs), so the node must still exist at that point and the ref/unref is required to ensure this. The root node of the BlockBackend can change, so without the ref/unref pair the last reference to the node can go away even if the BlockBackend still exists. So we'll need a different solution. Kevin