Re: [PATCH v5 3/4] KVM: s390: Change the fi->lock to a raw_spinlock for RT case

[Douglas Freimuth <freimuth@linux.ibm.com>]

On 5/6/26 12:57 AM, Heiko Carstens wrote:
> On Tue, May 05, 2026 at 07:37:27PM +0200, Douglas Freimuth wrote:
>> s390 needs to maintain support for an RT kernel. This requires the
>> floating interrupt lock, fi->lock to be changed to a raw spin lock
>> since the fi->lock maybe called with interrupts disabled in __inject_io.
>>
>> Signed-off-by: Douglas Freimuth <freimuth@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |  2 +-
>>   arch/s390/kvm/intercept.c        |  4 +-
>>   arch/s390/kvm/interrupt.c        | 68 ++++++++++++++++----------------
>>   arch/s390/kvm/kvm-s390.c         |  2 +-
>>   4 files changed, 38 insertions(+), 38 deletions(-)
> 
> s390 does not support RT, but I guess you are referring to a lockdep splat
> which you would see without doing this change, similar like we have seen at
> other places.
> 
> Can you include the relevant parts of the splat for reference, please?

Heiko, thank you for you response. I dont recall trapping it with 
lockdep (while it was on) but discussion on the mailing list in an 
earlier version made us look closer (and we saw it across the AI models 
that reviewed the patch.) It appears that while RT isn't supported it 
can still be compiled in to the kernel so we wanted to mitigate the 
issues we would add to if someone does that while not impacting non-RT 
environments, the main use case.