From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: [PATCH 1/7] vfio: Fix group release deadlock Date: Fri, 09 Jun 2017 15:59:34 -0600 Message-ID: <20170609215934.31986.87512.stgit@gimli.home> References: <20170609215816.31986.89321.stgit@gimli.home> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: eric.auger@redhat.com, alex.williamson@redhat.com, linux-kernel@vger.kernel.org To: kvm@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50850 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751738AbdFIV7y (ORCPT ); Fri, 9 Jun 2017 17:59:54 -0400 In-Reply-To: <20170609215816.31986.89321.stgit@gimli.home> Sender: kvm-owner@vger.kernel.org List-ID: If vfio_iommu_group_notifier() acquires a group reference and that reference becomes the last reference to the group, then vfio_group_put introduces a deadlock code path where we're trying to unregister from the iommu notifier chain from within a callout of that chain. Use a work_struct to release this reference asynchronously. Signed-off-by: Alex Williamson --- drivers/vfio/vfio.c | 37 ++++++++++++++++++++++++++++++++++++- 1 file changed, 36 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c index 561084ab387f..f2e24d5699f2 100644 --- a/drivers/vfio/vfio.c +++ b/drivers/vfio/vfio.c @@ -423,6 +423,34 @@ static void vfio_group_put(struct vfio_group *group) kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock); } +struct vfio_group_put_work { + struct work_struct work; + struct vfio_group *group; +}; + +static void vfio_group_put_bg(struct work_struct *work) +{ + struct vfio_group_put_work *do_work; + + do_work = container_of(work, struct vfio_group_put_work, work); + + vfio_group_put(do_work->group); + kfree(do_work); +} + +static void vfio_group_schedule_put(struct vfio_group *group) +{ + struct vfio_group_put_work *do_work; + + do_work = kmalloc(sizeof(*do_work), GFP_KERNEL); + if (WARN_ON(!do_work)) + return; + + INIT_WORK(&do_work->work, vfio_group_put_bg); + do_work->group = group; + schedule_work(&do_work->work); +} + /* Assume group_lock or group reference is held */ static void vfio_group_get(struct vfio_group *group) { @@ -762,7 +790,14 @@ static int vfio_iommu_group_notifier(struct notifier_block *nb, break; } - vfio_group_put(group); + /* + * If we're the last reference to the group, the group will be + * released, which includes unregistering the iommu group notifier. + * We hold a read-lock on that notifier list, unregistering needs + * a write-lock... deadlock. Release our reference asyncronously + * to avoid that situation. + */ + vfio_group_schedule_put(group); return NOTIFY_OK; }