From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754633AbaCCOd2 (ORCPT ); Mon, 3 Mar 2014 09:33:28 -0500 Received: from e24smtp03.br.ibm.com ([32.104.18.24]:42183 "EHLO e24smtp03.br.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754107AbaCCOdZ (ORCPT ); Mon, 3 Mar 2014 09:33:25 -0500 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: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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; -- 1.7.1