Re: [PATCH v2 0/3] Introduce arch_do_panic

[Mete Durlu <meted@linux.ibm.com>]

On 29/07/2026 10:56, Heiko Carstens wrote:
> On Mon, Jul 27, 2026 at 12:36:19PM +0200, Mete Durlu wrote:
>> Changes in v2 - Address Sashiko findings;
>> - Patch 2: Remove unused leftover code
>> - Patch 2: Mention panic_timeout and shutdown_actions relationship for
>>    s390 in commit message
>> - Patch 3: Use bug.h instead of setup.h to pass around arch_do_panic
>>    implementation of sparc
>>
>> Replace architecture-specific ifdef sections in vpanic() with a clean
>> arch_do_panic() hook. Currently s390 and sparc embed their panic
>> handlers directly in vpanic() using preprocessor conditionals, making
>> the common code path harder to maintain.
>>
>> Introduce arch_do_panic() as an architecture extension point called at
>> the end of vpanic(). Architectures can use this hook to implement their
>> specific panic handling without polluting the generic panic code.
>>
>> Move s390 panic handling from the panic_notifier chain to
>> arch_do_panic(). This corrects the execution order so that the
>> panic_timeout is properly evaluated before architecture-specific
>> actions. The previous notifier-based approach executed too early in the
>> panic sequence.
>>
>> Move sparc panic handling from ifdef blocks to arch_do_panic(). Remove
>> the preprocessor conditionals from vpanic() and place the Stop-A
>> enablement code in architecture-specific files where it belongs.
>>
>> The cleanup reduces vpanic() complexity and establishes a pattern for other
>> architectures needing custom panic behavior.
>>
>> Signed-off-by: Mete Durlu <meted@linux.ibm.com>
>> ---
>> Mete Durlu (3):
>>        panic: Introduce arch_do_panic
>>        s390: Implement arch_do_panic
>>        sparc: Implement arch_do_panic
>>
>>   arch/s390/include/asm/setup.h  |  3 +++
>>   arch/s390/kernel/ipl.c         | 15 +--------------
>>   arch/sparc/include/asm/bug.h   |  3 +++
>>   arch/sparc/include/asm/setup.h |  1 -
>>   arch/sparc/kernel/setup.c      |  8 ++++++++
>>   kernel/panic.c                 | 18 ++++++------------
>>   6 files changed, 21 insertions(+), 27 deletions(-)
> 
> Putting the define in a different header file per architecture doesn't
> seem to be a good idea. There is no guarantee that this will work. So
> either you find a common header file, where it is known that is (and
> will be) included in panic.c, or you go with a weak function.

I went over the headers included to panic.c, either they are really
irrelevant or not present on other archs. To me the best candidate
header seems like "asm/bug.h"

$ find ./arch/ -name "bug.h" | grep include/asm | wc -l
16

$ ls ./arch | wc -l
22 # actually 21 as we shouldn't count Kconfig file

The architectures missing bug.h in their include/asm/ directory are
hexagon, microblaze, nios2, um and xtensa

I believe 16/21 is a good ratio but if this is still not good
enough, I'd like to fallback to __weak implementation.

What do you think Heiko?