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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
