Re: [PATCH v2 0/3] Introduce arch_do_panic

[Mete Durlu]

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@xxxxxxxxxxxxx>
> > ---
> > 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?