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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 94E4FC43381 for ; Mon, 1 Apr 2019 17:39:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 702F620830 for ; Mon, 1 Apr 2019 17:39:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387915AbfDARj0 (ORCPT ); Mon, 1 Apr 2019 13:39:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1026 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388274AbfDARjX (ORCPT ); Mon, 1 Apr 2019 13:39:23 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F1E4630833C4; Mon, 1 Apr 2019 17:39:22 +0000 (UTC) Received: from gondolin (ovpn-117-29.ams2.redhat.com [10.36.117.29]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3FAD1600D4; Mon, 1 Apr 2019 17:39:19 +0000 (UTC) Date: Mon, 1 Apr 2019 19:39:16 +0200 From: Cornelia Huck To: Parav Pandit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kwankhede@nvidia.com, alex.williamson@redhat.com, cjia@nvidia.com Subject: Re: [PATCHv1 6/7] vfio/mdev: Fix aborting mdev child device removal if one fails Message-ID: <20190401193916.3d2c6552.cohuck@redhat.com> In-Reply-To: <1553658345-43995-7-git-send-email-parav@mellanox.com> References: <1553658345-43995-1-git-send-email-parav@mellanox.com> <1553658345-43995-7-git-send-email-parav@mellanox.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 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Mon, 01 Apr 2019 17:39:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 26 Mar 2019 22:45:44 -0500 Parav Pandit wrote: > device_for_each_child() stops executing callback function for remaining > child devices, if callback hits an error. > Each child mdev device is independent of each other. > While unregistering parent device, mdev core must remove all child mdev > devices. > Therefore, mdev_device_remove_cb() always returns success so that s/always returns/must always return/ ? > device_for_each_child doesn't abort if one child removal hits error. > > While at it, improve remove and unregister functions for below simplicity. > > There isn't need to pass forced flag pointer during mdev parent > removal which invokes mdev_device_remove(). So simplify the flow. > > mdev_device_remove() is called from two paths. > 1. mdev_unregister_driver() > mdev_device_remove_cb() > mdev_device_remove() > 2. remove_store() > mdev_device_remove() > > When device is removed by user using remote_store(), device under > removal is mdev device. > When device is removed during parent device removal using generic child > iterator, mdev check is already done using dev_is_mdev(). Isn't there still a possible race condition (which you seem to address with the following patch)? IOW, you cannot remove that loop-under-mutex yet? > > Hence, remove the unnecessary loop in mdev_device_remove(). > > Fixes: 7b96953bc640 ("vfio: Mediated device Core driver") > Reviewed-by: Maxim Levitsky > Signed-off-by: Parav Pandit > --- > drivers/vfio/mdev/mdev_core.c | 23 +++++------------------ > 1 file changed, 5 insertions(+), 18 deletions(-) > > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c > index 836d319..aefcf34 100644 > --- a/drivers/vfio/mdev/mdev_core.c > +++ b/drivers/vfio/mdev/mdev_core.c > @@ -149,10 +149,10 @@ static int mdev_device_remove_ops(struct mdev_device *mdev, bool force_remove) > Maybe add /* only called during parent device unregistration */ to avoid headscratching in the future? > static int mdev_device_remove_cb(struct device *dev, void *data) > { > - if (!dev_is_mdev(dev)) > - return 0; > + if (dev_is_mdev(dev)) > + mdev_device_remove(dev, true); > > - return mdev_device_remove(dev, data ? *(bool *)data : true); > + return 0; > } > > /* > @@ -240,7 +240,6 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops) > void mdev_unregister_device(struct device *dev) > { > struct mdev_parent *parent; > - bool force_remove = true; > > mutex_lock(&parent_list_lock); > parent = __find_parent_device(dev); > @@ -254,8 +253,7 @@ void mdev_unregister_device(struct device *dev) > list_del(&parent->next); > class_compat_remove_link(mdev_bus_compat_class, dev, NULL); > > - device_for_each_child(dev, (void *)&force_remove, > - mdev_device_remove_cb); > + device_for_each_child(dev, NULL, mdev_device_remove_cb); > > parent_remove_sysfs_files(parent); > Up to this chunk, the patch looks good to me. > @@ -348,24 +346,13 @@ int mdev_device_create(struct kobject *kobj, > > int mdev_device_remove(struct device *dev, bool force_remove) > { > - struct mdev_device *mdev, *tmp; > + struct mdev_device *mdev; > struct mdev_parent *parent; > struct mdev_type *type; > int ret; > > mdev = to_mdev_device(dev); > - > mutex_lock(&mdev_list_lock); > - list_for_each_entry(tmp, &mdev_list, next) { > - if (tmp == mdev) > - break; > - } > - > - if (tmp != mdev) { > - mutex_unlock(&mdev_list_lock); > - return -ENODEV; > - } > - > if (!mdev->active) { > mutex_unlock(&mdev_list_lock); > return -EAGAIN;