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[209.85.128.175]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e178e43fdabsm675117276.3.2024.08.23.06.13.54 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Aug 2024 06:13:54 -0700 (PDT) Received: by mail-yw1-f175.google.com with SMTP id 00721157ae682-6c3f1939d12so15082887b3.2 for ; Fri, 23 Aug 2024 06:13:54 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCWeabnwALFMaUx/J9CpdeQcl0wmnvsme+IWGWjwwE/7YcpuRjnx190a/BBENVX3WvoPdonJsNmzQF+/67s=@lists.ozlabs.org X-Received: by 2002:a05:690c:4d04:b0:6b1:3bf8:c161 with SMTP id 00721157ae682-6c62538d076mr24871437b3.13.1724418833900; Fri, 23 Aug 2024 06:13:53 -0700 (PDT) X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 References: <20240823125156.104775-1-dave@vasilevsky.ca> In-Reply-To: <20240823125156.104775-1-dave@vasilevsky.ca> From: Geert Uytterhoeven Date: Fri, 23 Aug 2024 15:13:42 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] crash: Default to CRASH_DUMP=n when support for it is unlikely To: Dave Vasilevsky Cc: glaubitz@physik.fu-berlin.de, bhe@redhat.com, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, mpe@ellerman.id.au, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, =?UTF-8?Q?Reimar_D=C3=B6ffinger?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Dave, On Fri, Aug 23, 2024 at 2:54=E2=80=AFPM Dave Vasilevsky 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=3Dn on sh. > > Signed-off-by: Dave Vasilevsky > Reported-by: Reimar D=C3=B6ffinger > 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=3Dy). For more details see Documentation/admin-guide/kdump/kdump.rst For s390, this option also enables zfcpdump. See also What is so special about CRASH_DUMP, that it should be enabled by default? Gr{oetje,eeting}s, Geert --=20 Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k= .org In personal conversations with technical people, I call myself a hacker. Bu= t when I'm talking to journalists I just say "programmer" or something like t= hat. -- Linus Torvalds