On Wed, Oct 11, 2017 at 03:35:56PM -0600, Alex Williamson wrote:
> When removing a device, for example a VF being removed due to SR-IOV
> teardown, a "soft" hot-unplug via 'echo 1 > remove' in sysfs, or an
> actual hot-unplug, we first remove the procfs and sysfs attributes
> for the device before attempting to release the device from any driver
> bound to it. Unbinding the driver from the device can take time. The
> device might need to write out data or it might be actively in use.
> If it's in use by userspace through a vfio driver, the unbind might
> block until the user releases the device. This leads to a potentially
> non-trivial amount of time where the device exists, but we've torn
> down the interfaces that userspace uses to examine devices, for
> instance lspci might generate this sort of error:
>
> pcilib: Cannot open /sys/bus/pci/devices/0000:01:0a.3/config
> lspci: Unable to read the standard configuration space header of device 0000:01:0a.3
>
> We don't seem to have any dependence on this teardown ordering in the
> kernel, so let's unbind the driver first, which is also more symmetric
> with the instantiation of the device.
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>
> Am I missing any reason for the existing ordering? Looking through
> history, it seems that we've simply always had this ordering. We're
> dealing only with pci related device attributes, so I can't figure
> how the current ordering protects us from any races. Anyway, I'd
> appreciate comments if there's something obvious I'm missing. Thanks.
Makes sense to me. Applied to pci/virtualization for v4.15, thanks!
> drivers/pci/remove.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 73a03d382590..2fa0dbde36b7 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -19,9 +19,9 @@ static void pci_stop_dev(struct pci_dev *dev)
> pci_pme_active(dev, false);
>
> if (dev->is_added) {
> + device_release_driver(&dev->dev);
> pci_proc_detach_device(dev);
> pci_remove_sysfs_dev_files(dev);
> - device_release_driver(&dev->dev);
> dev->is_added = 0;
> }
>
>
