On 6/16/2026 10:53 AM, Peter Oberparleiter wrote: > On 16.06.2026 11:16, Cornelia Huck wrote: >> 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? > As Halil also pointed out, this would be a programming error, either on > the side of the driver that starts I/O without setting the device > properly online, or in the common I/O layer (hopefully not, but you > never know). Having a dedicated return code to identify this situation > is definitely useful, and we'll also consider documenting it accordingly > in the function comment. > >>>>> 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? > I faintly remember that there WAS a reason to use the remainder of the > SCHIB contents because of some unwanted effect that occurred if we > didn't, but I don't recall the details. We'll need to dig up the > associated bug report to understand it and determine if we can simply > clear all of the SCHIB, or need to keep some of the information intact. > >>>>> 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(). > Yeah, this was definitely an unexpected side effect of the DNV commit. > FWIW, during my testing, that was indeed the only situation in which I saw -EINVAL during the detach process. So assuming the right fix would correctly return ENODEV, I agree this patch is likely unnecessary.
Thanks all.
