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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 DC4A9C4321D for ; Fri, 17 Aug 2018 08:43:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9480821893 for ; Fri, 17 Aug 2018 08:43:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9480821893 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726395AbeHQLqN (ORCPT ); Fri, 17 Aug 2018 07:46:13 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35740 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725845AbeHQLqN (ORCPT ); Fri, 17 Aug 2018 07:46:13 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 39608401EF1B; Fri, 17 Aug 2018 08:43:40 +0000 (UTC) Received: from gondolin (dhcp-192-222.str.redhat.com [10.33.192.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id BEB432026D6C; Fri, 17 Aug 2018 08:43:33 +0000 (UTC) Date: Fri, 17 Aug 2018 10:43:31 +0200 From: Cornelia Huck To: Tony Krowiak Cc: Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com, fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com, frankja@linux.ibm.com Subject: Re: [PATCH v9 09/22] s390: vfio-ap: register matrix device with VFIO mdev framework Message-ID: <20180817104331.378fa130.cohuck@redhat.com> In-Reply-To: <5b77a5e9-6d91-c7a3-5ada-d888735f0488@linux.ibm.com> References: <1534196899-16987-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1534196899-16987-10-git-send-email-akrowiak@linux.vnet.ibm.com> <20180814131929.37d4b530.cohuck@redhat.com> <5b77a5e9-6d91-c7a3-5ada-d888735f0488@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 2.78 on 10.11.54.4 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Fri, 17 Aug 2018 08:43:40 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Fri, 17 Aug 2018 08:43:40 +0000 (UTC) for IP:'10.11.54.4' DOMAIN:'int-mx04.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'cohuck@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Aug 2018 12:24:16 -0400 Tony Krowiak wrote: > On 08/14/2018 07:19 AM, Cornelia Huck wrote: > > On Mon, 13 Aug 2018 17:48:06 -0400 > > Tony Krowiak wrote: > >> +static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev) > >> +{ > >> + struct ap_matrix_mdev *matrix_mdev; > >> + > >> + matrix_mdev = kzalloc(sizeof(*matrix_mdev), GFP_KERNEL); > >> + if (!matrix_mdev) > >> + return -ENOMEM; > >> + > >> + matrix_mdev->name = dev_name(mdev_dev(mdev)); > >> + vfio_ap_matrix_init(&matrix_dev.info, &matrix_mdev->matrix); > >> + mdev_set_drvdata(mdev, matrix_mdev); > >> + > >> + if (atomic_dec_if_positive(&matrix_dev.available_instances) < 0) { > >> + kfree(matrix_mdev); > >> + return -EPERM; > >> + } > > Maybe move this check to the top of the function? > > Please ignore my previous response to your comment. I can't move the call to > atomic_dec_if_positive() to the top of the function because it > decrements the > available_instances and if the kzalloc() of matrix_mdev fails, then the > value > would have to then be incremented to remain valid. What I can do is this: > > 1. Check the value of available_instances using atomic_read() at the top of > the function and if it is zero, return an error. > > 2. Replace the call to atomic_dec_if_positive() with a call to atomic_dec() > to decrement the available_instances. > > I agree that it makes sense to return before attempting to allocate the > matrix_mdev if available_instances is zero. Wouldn't that be racy, though? I don't think re-incrementing the counter is too bad, and it's certainly better than going through allocation/freeing of structures. > > > > >> + > >> + mutex_lock(&matrix_dev.lock); > >> + list_add(&matrix_mdev->list, &matrix_dev.mdev_list); > >> + mutex_unlock(&matrix_dev.lock); > >> + > >> + return 0; > >> +} > >