Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966989AbcLVUWC (ORCPT ); Thu, 22 Dec 2016 15:22:02 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48064 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966970AbcLVUV6 (ORCPT ); Thu, 22 Dec 2016 15:21:58 -0500 Subject: [PATCH v2 1/4] vfio-mdev: Fix remove race From: Alex Williamson To: alex.williamson@redhat.com Cc: jike.song@intel.com, kwankhede@nvidia.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Date: Thu, 22 Dec 2016 13:21:57 -0700 Message-ID: <20161222202157.15541.12925.stgit@gimli.home> In-Reply-To: <20161222201809.15541.22506.stgit@gimli.home> References: <20161222201809.15541.22506.stgit@gimli.home> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Thu, 22 Dec 2016 20:21:58 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3016 Lines: 99 Using the mtty mdev sample driver we can generate a remove race by starting one shell that continuously creates mtty devices and several other shells all attempting to remove devices, in my case four remove shells. The fault occurs in mdev_remove_sysfs_files() where the passed type arg is NULL, which suggests we've received a struct device in mdev_device_remove() but it's in some sort of teardown state. The solution here is to make use of the accidentally unused list_head on the mdev_device such that the mdev core keeps a list of all the mdev devices. This allows us to validate that we have a valid mdev before we start removal, remove it from the list to prevent others from working on it, and if the vendor driver refuses to remove, we can re-add it to the list. Cc: Kirti Wankhede Signed-off-by: Alex Williamson --- drivers/vfio/mdev/mdev_core.c | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c index be1ee89..6bb4d4c 100644 --- a/drivers/vfio/mdev/mdev_core.c +++ b/drivers/vfio/mdev/mdev_core.c @@ -27,6 +27,9 @@ static DEFINE_MUTEX(parent_list_lock); static struct class_compat *mdev_bus_compat_class; +static LIST_HEAD(mdev_list); +static DEFINE_MUTEX(mdev_list_lock); + static int _find_mdev_device(struct device *dev, void *data) { struct mdev_device *mdev; @@ -316,6 +319,11 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid) dev_dbg(&mdev->dev, "MDEV: created\n"); mutex_unlock(&parent->lock); + + mutex_lock(&mdev_list_lock); + list_add(&mdev->next, &mdev_list); + mutex_unlock(&mdev_list_lock); + return ret; create_failed: @@ -329,12 +337,30 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid) int mdev_device_remove(struct device *dev, bool force_remove) { - struct mdev_device *mdev; + struct mdev_device *mdev, *tmp; struct parent_device *parent; struct mdev_type *type; int ret; + bool found = false; mdev = to_mdev_device(dev); + + mutex_lock(&mdev_list_lock); + list_for_each_entry(tmp, &mdev_list, next) { + if (tmp == mdev) { + found = true; + break; + } + } + + if (found) + list_del(&mdev->next); + + mutex_unlock(&mdev_list_lock); + + if (!found) + return -ENODEV; + type = to_mdev_type(mdev->type_kobj); parent = mdev->parent; mutex_lock(&parent->lock); @@ -342,6 +368,11 @@ int mdev_device_remove(struct device *dev, bool force_remove) ret = mdev_device_remove_ops(mdev, force_remove); if (ret) { mutex_unlock(&parent->lock); + + mutex_lock(&mdev_list_lock); + list_add(&mdev->next, &mdev_list); + mutex_unlock(&mdev_list_lock); + return ret; } @@ -349,7 +380,8 @@ int mdev_device_remove(struct device *dev, bool force_remove) device_unregister(dev); mutex_unlock(&parent->lock); mdev_put_parent(parent); - return ret; + + return 0; } static int __init mdev_init(void)