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Message-ID: <CAMuHMdVYNhFJ+qBDP3_fi9oeHsgOL0vqPe1YqE18+M8n1onssw@mail.gmail.com>
Date: Fri, 23 Aug 2024 15:13:42 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Dave Vasilevsky <dave@...ilevsky.ca>
Cc: glaubitz@...sik.fu-berlin.de, bhe@...hat.com,
linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org, mpe@...erman.id.au,
kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
Reimar Döffinger <Reimar.Doeffinger@....de>
Subject: Re: [PATCH] crash: Default to CRASH_DUMP=n when support for it is unlikely
Hi Dave,
On Fri, Aug 23, 2024 at 2:54 PM Dave Vasilevsky <dave@...ilevsky.ca> wrote:
> Fixes boot failures on 6.9 on PPC_BOOK3S_32 machines using
> Open Firmware. On these machines, the kernel refuses to boot
> from non-zero PHYSICAL_START, which occurs when CRASH_DUMP is on.
>
> Since most PPC_BOOK3S_32 machines boot via Open Firmware, it should
> default to off for them. Users booting via some other mechanism
> can still turn it on explicitly.
>
> Also defaults to CRASH_DUMP=n on sh.
>
> Signed-off-by: Dave Vasilevsky <dave@...ilevsky.ca>
> Reported-by: Reimar Döffinger <Reimar.Doeffinger@....de>
> Closes: https://lists.debian.org/debian-powerpc/2024/07/msg00001.html
> Fixes: 75bc255a7444 ("crash: clean up kdump related config items")
Thanks for your patch!
> --- a/kernel/Kconfig.kexec
> +++ b/kernel/Kconfig.kexec
> @@ -97,7 +97,7 @@ config KEXEC_JUMP
>
> config CRASH_DUMP
> bool "kernel crash dumps"
> - default y
> + default ARCH_DEFAULT_CRASH_DUMP
> depends on ARCH_SUPPORTS_CRASH_DUMP
> depends on KEXEC_CORE
> select VMCORE_INFO
IMHO CRASH_DUMP should just default to n, like most kernel options, as
it enables non-trivial extra functionality: the kernel source tree has
more than 100 locations that check if CONFIG_CRASH_DUMP is enabled.
Letting it default to enabled also conflicts with the spirit of the
help text for the symbol:
Generate crash dump after being started by kexec.
This should be normally only set in special crash dump kernels
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
which are loaded in the main kernel with kexec-tools into
a specially reserved region and then later executed after
a crash by kdump/kexec. The crash dump kernel must be compiled
to a memory address not used by the main kernel or BIOS using
PHYSICAL_START, or it must be built as a relocatable image
(CONFIG_RELOCATABLE=y).
For more details see Documentation/admin-guide/kdump/kdump.rst
For s390, this option also enables zfcpdump.
See also <file:Documentation/arch/s390/zfcpdump.rst>
What is so special about CRASH_DUMP, that it should be enabled by
default?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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