Re: [PATCH v1] s390/virtio_ccw: Also suppress -EINVAL on device detach

[William Bezenah <wbezenah@linux.ibm.com>]

On 6/15/2026 10:58 AM, Cornelia Huck wrote:
> On Mon, Jun 15 2026, Halil Pasic <pasic@linux.ibm.com> wrote:
>
>> On Fri, 12 Jun 2026 17:54:07 +0200
>> William Bezenah <wbezenah@linux.ibm.com> wrote:
>>
>>> Since commit 8c58a229688c ("s390/cio: Do not unregister the
>>> subchannel based on DNV"), subchannel behavior following a device
>>> detach has been updated and results in -EINVAL being propagated
>>> rather than -ENODEV, originating from ccw_device_start_timeout_key()
>>> in cio/device_ops. In the end, the virtio driver has no ability to
>>> react to the difference between device and subchannel states here,
>>> and during detach, both -ENODEV and -EINVAL indicate the device
>>> cannot be used and should not be treated as errors requiring
>>> attention. Update error handling in virtio_ccw_del_vq() and
>>> virtio_ccw_drop_indicator() to suppress -EINVAL in addition to
>>> -ENODEV.
>> Hi William!
>>
>> Are you saying that ccw_device_start() started returning -EINVAL
>> since 8c58a229688c ("s390/cio: Do not unregister the subchannel based on
>> DNV")? Or did I somehow read the paragraph wrong?
>>
>> The funcition ccw_device_start is documented to return:
>>  * Returns:                                                                     
>>  *  %0, if the operation was successful;                                        
>>  *  -%EBUSY, if the device is busy, or status pending;                          
>>  *  -%EACCES, if no path specified in @lpm is operational;                      
>>  *  -%ENODEV, if the device is not operational. 
>> and the commit message does not say a thing about introducing -EINVAL to
>> the mix.
> The function may return -EINVAL for non-enabled subchannels
> (i.e. pmcw.ena == 0), maybe we get an all-zeroes schib with dnv == 0?
> I'd expect it not to be enabled in that case anyway.

Yep, that's at least how I've come to understand what changed. The
function ccw_device_start_timeout_key() has always returned -EINVAL
for non-enabled subchannels (pmcw.ena == 0), though it's not
documented in the header.

What changed with commit 8c58a229688c is that cio_update_schib() now
updates the schib even when DNV=0, rather than returning early as it
did previously. Somehow this update results in pmcw.ena == 0 in
ccw_device_start_timeout_key(). Previously, it saw pmcw.ena == 1 and
moved to the condition (cdev->private->state == DEV_STATE_NOT_OPER)
where it returned -ENODEV.

So the commit didn't introduce -EINVAL as a new return value, rather,
it changed the subchannel lifecycle such that existing paths now
propagate -EINVAL rather than -ENODEV during the device detach
scenario.