Re: [PATCH v2 1/7] s390/kdump: implement is_kdump_kernel()

[David Hildenbrand]

On 15.10.24 10:30, Heiko Carstens wrote:
> On Mon, Oct 14, 2024 at 09:26:03PM +0200, David Hildenbrand wrote:
> > On 14.10.24 20:20, Heiko Carstens wrote:
> > > Looks like this could work. But the comment in smp.c above
> > > dump_available() needs to be updated.
> >
> > A right, I remember that there was some outdated documentation.
> >
> > > Are you willing to do that, or should I provide an addon patch?
> >
> > I can squash the following:
> >
> > diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> > index 4df56fdb2488..a4f538876462 100644
> > --- a/arch/s390/kernel/smp.c
> > +++ b/arch/s390/kernel/smp.c
> > @@ -587,16 +587,16 @@ int smp_store_status(int cpu)
> >    *    with sigp stop-and-store-status. The firmware or the boot-loader
> >    *    stored the registers of the boot CPU in the absolute lowcore in the
> >    *    memory of the old system.
> > - * 3) kdump and the old kernel did not store the CPU state,
> > - *    or stand-alone kdump for DASD
> > - *    condition: OLDMEM_BASE != NULL && !is_kdump_kernel()
> > + * 3) kdump or stand-alone kdump for DASD
> > + *    condition: OLDMEM_BASE != NULL && !is_ipl_type_dump() == false
> >    *    The state for all CPUs except the boot CPU needs to be collected
> >    *    with sigp stop-and-store-status. The kexec code or the boot-loader
> >    *    stored the registers of the boot CPU in the memory of the old system.
> > - * 4) kdump and the old kernel stored the CPU state
> > - *    condition: OLDMEM_BASE != NULL && is_kdump_kernel()
> > - *    This case does not exist for s390 anymore, setup_arch explicitly
> > - *    deactivates the elfcorehdr= kernel parameter
> > + *
> > + * Note that the old Kdump mode where the old kernel stored the CPU state
>
> To be consistent with the rest of the comment, please write kdump in
> all lower case characters, please.

It obviously was too late in the evening for me :) Thanks!

> > + * does no longer exist: setup_arch explicitly deactivates the elfcorehdr=
> > + * kernel parameter. The is_kudmp_kernel() implementation on s390 is independent
>
> Typo: kudmp.
>
> > Does that sound reasonable? I'm not so sure about the "2) stand-alone kdump for
> > SCSI/NVMe (zfcp/nvme dump with swapped memory)": is that really "kdump" ?
>
> Yes, it is some sort of kdump, even though a bit odd.

My concern is that we'll now have

bool is_kdump_kernel(void)
{
       return oldmem_data.start && !is_ipl_type_dump();
}

Which matches 3), but if 2) is also called "kdump", then should it 
actually be

bool is_kdump_kernel(void)
{
       return oldmem_data.start;
}

?

When I wrote that code I was rather convinced that the variant in this 
patch is the right thing to do.

--
Cheers,

David / dhildenb