From patchwork Mon Mar 3 14:33:12 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thadeu Lima de Souza Cascardo X-Patchwork-Id: 325850 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 0C25C2C00D5 for ; Tue, 4 Mar 2014 01:33:27 +1100 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754399AbaCCOd0 (ORCPT ); Mon, 3 Mar 2014 09:33:26 -0500 Received: from e24smtp03.br.ibm.com ([32.104.18.24]:42184 "EHLO e24smtp03.br.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753980AbaCCOdZ (ORCPT ); Mon, 3 Mar 2014 09:33:25 -0500 Received: from /spool/local by e24smtp03.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 3 Mar 2014 11:33:23 -0300 Received: from d24dlp01.br.ibm.com (9.18.248.204) by e24smtp03.br.ibm.com (10.172.0.139) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Mon, 3 Mar 2014 11:33:20 -0300 Received: from d24relay01.br.ibm.com (d24relay01.br.ibm.com [9.8.31.16]) by d24dlp01.br.ibm.com (Postfix) with ESMTP id 9AE2F352006E; Mon, 3 Mar 2014 09:33:15 -0500 (EST) Received: from d24av03.br.ibm.com (d24av03.br.ibm.com [9.8.31.95]) by d24relay01.br.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s23EXIDv4919542; Mon, 3 Mar 2014 11:33:19 -0300 Received: from d24av03.br.ibm.com (localhost [127.0.0.1]) by d24av03.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s23EXGfB019298; Mon, 3 Mar 2014 11:33:16 -0300 Received: from oc0268524204.ibm.com ([9.8.14.85]) by d24av03.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id s23EXFp1019266; Mon, 3 Mar 2014 11:33:15 -0300 From: Thadeu Lima de Souza Cascardo To: alex.williamson@redhat.com Cc: bhelgaas@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, aik@ozlabs.ru, Thadeu Lima de Souza Cascardo Subject: [RFC PATCH] vfio-pci: avoid deadlock between unbind and VFIO_DEVICE_RESET Date: Mon, 3 Mar 2014 11:33:12 -0300 Message-Id: <1393857192-28360-1-git-send-email-cascardo@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.1 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14030314-9564-0000-0000-0000003968BB Sender: kvm-ppc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm-ppc@vger.kernel.org When we unbind vfio-pci from a device, while running a guest, we might have a deadlock when such a guest reboots. Unbind takes device_lock at device_release_driver, and waits for release_q at vfio_del_group_dev. release_q will only be woken up when all references to vfio_device are gone, and that includes open file descriptors, like the ones a guest on qemu will hold. If you try to reboot the guest, it will call VFIO_DEVICE_RESET, which calls pci_reset_function, which now grabs the device_lock, and we are deadlocked. Using device_trylock allow us to handle the case when the lock is already taken, and avoid this situation. Signed-off-by: Thadeu Lima de Souza Cascardo --- Not tested yet, but I would like some comments now, like would it be better to have a pci_try_reset_function, or do trylock on pci_reset_function itself? --- drivers/vfio/pci/vfio_pci.c | 14 ++++++++++++-- 1 files changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c index 3b76dc8..d1d2242 100644 --- a/drivers/vfio/pci/vfio_pci.c +++ b/drivers/vfio/pci/vfio_pci.c @@ -513,8 +513,18 @@ static long vfio_pci_ioctl(void *device_data, return ret; } else if (cmd == VFIO_DEVICE_RESET) { - return vdev->reset_works ? - pci_reset_function(vdev->pdev) : -EINVAL; + struct pci_dev *pdev = vdev->pdev; + int ret = -EBUSY; + if (!vdev->reset_works) + return -EINVAL; + if (pci_cfg_access_trylock(pdev)) { + if (device_trylock(&pdev->dev)) { + ret = __pci_reset_function_locked(pdev); + device_unlock(&pdev->dev); + } + pci_cfg_access_unlock(pdev); + } + return ret; } else if (cmd == VFIO_DEVICE_GET_PCI_HOT_RESET_INFO) { struct vfio_pci_hot_reset_info hdr;