Re: [PATCH v2 2/3] s390: Implement arch_do_panic

[Sven Schnelle]

Bradley Morgan <include@xxxxxxxxx> writes:

> On 28 July 2026 11:43:17 BST, Mete Durlu <meted@xxxxxxxxxxxxx> wrote:
>>On 27/07/2026 15:01, Bradley Morgan wrote:
>>
>>Hi Bradley,
>>
>>>> This now means that the panic_timeout value takes precedence over user
>>>> defined on_panic behavior.
>>> 
>>> this is the part i want to poke at. distros routinely ship panic=N on
>>> the cmdline. with this change, anyone who configured on_panic=dump on
>>> such a system silently stops getting dumps, because
>>> emergency_restart() runs first and never returns. a reboot instead of
>>> the dump you explicitly asked for is strictly worse. if you and Sven
>>> want that semantic, fine, but spell it out properly and give the s390
>>> docs for on_panic a line about the new precedence.
>>
>>FWICT, there is no mention of shutdown actions in kernel documentation.
>>s390's user documentation is a different story. I agree it should be
>>documented on Linux on IBM systems documentation.
>>
>>I'd argue that specifying both on_panic=dump and panic=N (N>0) is
>>a configuration error, but maybe a pr_warn() could be added to the
>>when on_panic=dump is configured with panic=N is set. That could
>>hint what is wrong if anyone investigating dmesg and trying to
>>figure out why system didn't dump.
>>
>
>
> hey, sorry I'm out, so I can't do the most massive think ever, and I may
> embarrass myself, heh.
>
> I think a BUG would be sufficient, we would want to shut down the system
> with said bug, I know about panic on warn, but sometimes that's not always
> enabled, something like a BUG would be good, what do you think?

Err... No. You don't want to make a mistake while updating the kernel
panic parameters just to figure out that on the next boot the kernel just BUGs()
because of that. There are of course lots of reasons why changing the kernel
command line could end up in a non-bootable system but this one would
be ridiculous.