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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 A9933C433E0 for ; Fri, 15 May 2020 09:59:29 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7C5272074D for ; Fri, 15 May 2020 09:59:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C5272074D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 57ED187D3D; Fri, 15 May 2020 09:59:29 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 7pOoVxx_z0TL; Fri, 15 May 2020 09:59:24 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by fraxinus.osuosl.org (Postfix) with ESMTP id B97CB87D01; Fri, 15 May 2020 09:59:24 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 840E4C0859; Fri, 15 May 2020 09:59:24 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 38BCAC016F for ; Fri, 15 May 2020 09:59:23 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 351AE8695F for ; Fri, 15 May 2020 09:59:23 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Cv+jOJq2U2bt for ; Fri, 15 May 2020 09:59:22 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by whitealder.osuosl.org (Postfix) with ESMTPS id 97E22867F0 for ; Fri, 15 May 2020 09:59:22 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id 18A43379; Fri, 15 May 2020 11:59:21 +0200 (CEST) Date: Fri, 15 May 2020 11:59:19 +0200 From: Joerg Roedel To: "Prakhya, Sai Praneeth" Subject: Re: [PATCH] iommu: Remove functions that support private domain Message-ID: <20200515095919.GQ18353@8bytes.org> References: <20200513224721.20504-1-sai.praneeth.prakhya@intel.com> <20200514131315.GJ18353@8bytes.org> <20200514183233.GO18353@8bytes.org> <20200514195615.GP18353@8bytes.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "iommu@lists.linux-foundation.org" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Thu, May 14, 2020 at 11:12:52PM +0000, Prakhya, Sai Praneeth wrote: > +static int is_driver_bound(struct device *dev, void *not_used) > +{ > + int ret = 0; > + > + device_lock(dev); > + if (device_is_bound(dev)) > + ret = 1; > + device_unlock(dev); > + return ret; > +} This locks only one device, so without lock-conversion there could be a driver probe after the device_unlock(), while we are probing the other devices of the group. > [SNIP] > > + /* > + * Check if any device in the group still has a driver binded to it. > + * This might race with device driver probing code and unfortunately > + * there is no clean way out of that either, locking all devices in the > + * group and then do the re-attach will introduce a lock-inversion with > + * group->mutex - Joerg. > + */ > + if (iommu_group_for_each_dev(group, NULL, is_driver_bound)) { > + pr_err("Active drivers exist for devices in the group\n"); > + return -EBUSY; > + } The lock inversion comes into the picture when this code is called from device(-driver) core through the bus-notifiers. The notifiers are called with the device already locked. > Another question I have is.. if it's racy then it should be racy even > for one device iommu groups.. right? Why would it be racy only with > multiple devices iommu group? Valid point. So the device needs to be locked _while_ the default domain change happens. If triggered by sysfs there should be no locking problems, I guess. But you better try it out. Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu