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

[David Hildenbrand <david@redhat.com>]

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 A right, I remember that there was some outdated documentation.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