Re: [PATCH 6/6] Dont always remove XenFilt from UpperFilters

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 17/06/2021 13:33, Owen Smith wrote:
> There is a race which can prevent XenFilt from having AddDevice
> correctly called on some devices. This seems to happen more frequently
> after driver upgrades.
> It seems this is due to XenBus!DriverEntry removing XenFilt before
> XenBus!AddDevice inserts XenFilt into the UpperFilters value. In this
> gap, PnP manager can sample the UpperFilters key and fail to bind
> XenFilt to the required device stacks. This leads to XenFilt failing
> to determine the active device, which prevents the device unplugs
> from occuring, leading to a constant cycle of reboot prompts from
> xenbus_monitor.
>
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
This is a partial reversion of 9d28a9e9b798f "Avoid removing filters on 
upgrade installations". I think you need to state why that commit was 
wrong (assuming it was).
  Paul

> ---
>   src/xenbus/driver.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/src/xenbus/driver.c b/src/xenbus/driver.c
> index 1b621fa..e66bf45 100644
> --- a/src/xenbus/driver.c
> +++ b/src/xenbus/driver.c
> @@ -296,6 +296,9 @@ DriverRemoveFunctionDeviceObject(
>       RemoveEntryList(&Dx->ListEntry);
>       ASSERT3U(Driver.References, !=, 0);
>       References = --Driver.References;
> +
> +    if (References == 1)
> +        FiltersUninstall();
>   }
>   
>   //
> @@ -859,16 +862,15 @@ DriverEntry(
>                         MICRO_VERSION,
>                         BUILD_NUMBER);
>       if (!NT_SUCCESS(status)) {
> -        if (status == STATUS_INCOMPATIBLE_DRIVER_BLOCKED)
> +        if (status == STATUS_INCOMPATIBLE_DRIVER_BLOCKED) {
> +            // Re-instate XenFilt to avoid a second required reboot
> +            FiltersInstall();
>               __DriverRequestReboot();
> +        }
>   
>           goto done;
>       }
>   
> -    // Remove the filters from the registry. They will be re-instated by
> -    // the first successful AddDevice.
> -    FiltersUninstall();
> -
>       DriverObject->DriverExtension->AddDevice = DriverAddDevice;
>   
>       for (Index = 0; Index <= IRP_MJ_MAXIMUM_FUNCTION; Index++) {