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

[Halil Pasic <pasic@linux.ibm.com>]

On Mon, 15 Jun 2026 16:01:55 -0400
William Bezenah <wbezenah@linux.ibm.com> wrote:

> 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.

Wasn't his -EINVAL actually introduced by commit:
823d494ac111 ("[S390] pm: ccw bus power management callbacks")?

> 
> 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.

Sounds fishy to me. As far as I understand the DNV takes precedence over
all other pieces of PMCW.

> 
> 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.
> 

I'm not convinced returning -EINVAL in the given situation is the
right thing to do. Peter, would you mind to chime in?

Regards,
Halil