On Tue, Jun 16 2026, Peter Oberparleiter <[email protected]> wrote:
> On 15.06.2026 23:42, Halil Pasic wrote: >> On Mon, 15 Jun 2026 16:01:55 -0400 >> William Bezenah <[email protected]> wrote: >> >>> On 6/15/2026 10:58 AM, Cornelia Huck wrote: >>>> On Mon, Jun 15 2026, Halil Pasic <[email protected]> wrote: >>>> >>>>> On Fri, 12 Jun 2026 17:54:07 +0200 >>>>> William Bezenah <[email protected]> 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")? > > In the context of virtio-ccw added in 2012, an EINVAL return code > introduced in 2009 might be considered "always" :) :) I'm wondering whether we should still expect to hit the "ssch with ena==0" situation, given that pm support has been removed again in the meanwhile. (Well, other than in situations like this, where it is a follow-up to other problems.) IOW, can callers expect not to see -EINVAL, unless they are doing something really stupid? > >>> 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. > > And you're right about that! The Principles of Operation states (p. 15-4 > in SA22-7832-14 [1]) that the contents of all other fields in the PMCW > are unpredictable when DNV is 0, therefore 8c58a229688c is in error. > > I'll work with Vineeth to determine how to fix this issue, potentially > via manually clearing some relevant SCHIB fields instead of copying the > unpredictable results of the STSCH instruction. Can't you zero the whole SCHIB, or do you still need some of the measurement block things for cleanup? > >>> 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? > > I tend to agree that an attempt to start I/O for a subchannel that has > DNV 0 should result in ENODEV rather than EINVAL, though the latter is > still valid when a driver tries to start I/O on a subchannel that is not > enabled for I/O. > > We'll make sure to design the fix for 8c58a229688c in away that ENODEV > will be returned when DNV is 0. Assuming that this is the only situation > where virtio-ccw's ccw_io_helper() receives -EINVAL from > ccw_device_start__timeout_key() during detach, the subject patch should > no longer be necessary. I agree, I'd not expect to get -EINVAL in ccw_io_helper().
