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

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.

On another note, dumping via shutdown actions serves as a backup
and kdump is the main dump mechanism nowadays. Kdump always takes
precedence over panic=N.

> also worth saying in the changelog what this actually wins: today the
> INT_MIN notifier never returns, so sys_info, kmsg_dump, the post
> notifier crash_kexec path, the console flushes and the end banner
> never execute on s390 once on_panic fires. after this patch they all
> do. thats the headline and the changelog undersells it.
> 

Right, I will add that part to the commit message too.

>> Fixes: ff6b8ea68f4b ("[S390] ipl/dump on panic.")
> 
> What's broken? What's buggy? 

I can put a couple of sentences on how and why panic=
kernel command line argument was broken for s390.
> s/now allow/now allows/ in the changelog..

Will fix in next version!

Thank you