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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 5EC29C2BB85 for ; Thu, 16 Apr 2020 09:34:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A8A621D79 for ; Thu, 16 Apr 2020 09:34:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Gniz1jrT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2503664AbgDPJeU (ORCPT ); Thu, 16 Apr 2020 05:34:20 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:56607 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2503627AbgDPJeL (ORCPT ); Thu, 16 Apr 2020 05:34:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587029648; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=c0IPo0Ds7AJ1DPz8eMpn9oh2qqiK1Lq47iTdtzhbLqA=; b=Gniz1jrTBTi4yHD3V8vzE50KqILdfDjeF1VFsF7JwkL3QKruWMDUjwVymyKj9GGu4Dl+PU 1MLA8G5QliAFBkERmwtevLStt2cRDGQ+FIgi14H4ZBb1YVVbF0lNL9DcSuzdB/8ZyxsEwp wynhBA3Ds3/CTjTUNZYkf5DVxK2P3hI= 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-379-tprWSifANDOm2c09AFcakQ-1; Thu, 16 Apr 2020 05:34:06 -0400 X-MC-Unique: tprWSifANDOm2c09AFcakQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 22FDF107B769; Thu, 16 Apr 2020 09:34:04 +0000 (UTC) Received: from gondolin (ovpn-112-234.ams2.redhat.com [10.36.112.234]) by smtp.corp.redhat.com (Postfix) with ESMTP id B1BBD5DA2C; Thu, 16 Apr 2020 09:33:58 +0000 (UTC) Date: Thu, 16 Apr 2020 11:33:56 +0200 From: Cornelia Huck To: Harald Freudenberger Cc: Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pmorel@linux.ibm.com, pasic@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, jjherne@linux.ibm.com, fiuczy@linux.ibm.com Subject: Re: [PATCH v7 03/15] s390/zcrypt: driver callback to indicate resource in use Message-ID: <20200416113356.28fcef8c.cohuck@redhat.com> In-Reply-To: <82675d5c-4901-cbd8-9287-79133aa3ee68@linux.ibm.com> References: <20200407192015.19887-1-akrowiak@linux.ibm.com> <20200407192015.19887-4-akrowiak@linux.ibm.com> <20200414145851.562867ae.cohuck@redhat.com> <82675d5c-4901-cbd8-9287-79133aa3ee68@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 15 Apr 2020 08:08:24 +0200 Harald Freudenberger wrote: > On 14.04.20 14:58, Cornelia Huck wrote: > > On Tue, 7 Apr 2020 15:20:03 -0400 > > Tony Krowiak wrote: > >> + /* The non-default driver's module must be loaded */ > >> + if (!try_module_get(drv->owner)) > >> + return 0; > > Is that really needed? I would have thought that the driver core's > > klist usage would make sure that the callback would not be invoked for > > drivers that are not registered anymore. Or am I missing a window? > The try_module_get() and module_put() is a result of review feedback from > my side. The ap bus core is static in the kernel whereas the > vfio dd is a kernel module. So there may be a race condition between > calling the callback function and removal of the vfio dd module. > There is similar code in zcrypt_api which does the same for the zcrypt > device drivers before using some variables or functions from the modules. > Help me, it this is outdated code and there is no need to adjust the > module reference counter any more, then I would be happy to remove > this code :-) I think the driver core already should keep us safe. A built-in bus calling a driver in a module is a very common pattern, and I think ->owner was introduced exactly for that case. Unless I'm really missing something obvious?