[PATCH] Documentation: kdump: describe jumping to dump-capture kernel
dyoung at redhat.com
Tue Feb 13 17:43:29 PST 2018
On 02/13/18 at 04:22pm, Gioh Kim wrote:
> Jumping between the system kernel and the dump-capture kernel
> has been supported for long time but there is no description
> how to use it. This patch adds the description how to use kexec tool
> to jump to the dump-capture kernel and jump back to the system kernel.
I do not think this should belong to kdump documentation. There are a
lot of choices after a vmcore saving, one can reboot, halt, even go
ahead with real root filesystem init path. We do not need to document
all these in kdump.txt.
Since it is a general use case not only for kdump, add more info in
kexec man page would be better.
> Signed-off-by: Gioh Kim <gi-oh.kim at profitbricks.com>
> Documentation/kdump/kdump.txt | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index 51814450a7f8..35b71fef5d88 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -460,6 +460,44 @@ and the system will boot into the dump-capture kernel.
> For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
> "echo c > /proc/sysrq-trigger" or write a module to force the panic.
> +Jump between the System kernel and the Dump-capture kernel
> +Without system crash, the system can jump to the dump-capture kernel.
> +1) Enable "jump between system kernel and dump-capture kernel" support under
> + "Processor type and features"
> + CONFIG_KEXEC_JUMP=y
> +2) Load the dump-capture kernel with --load-preserve-context and mem-max
> + options as following.
> + kexec -l <dump-capture-kernel-vmlinux-image> \
> + --initrd=<initrd-for-dump-capture-kernel> --args-linux \
> + --append="root=<root-dev> <arch-specific-options>" \
> + --load-preserve-context \
> + --mem-max=<the highest memory address addr to load code into>
> +3) Jump to the loaded kernel
> + kexec -e
> +Now the system is running with the dump-capture kernel. You can jump back
> +to the system kernel.
> +1) Find kexec_jump_back_entry address in kernel booting parameters in
> + /proc/cmdline. That is the address for kexec to jump to. For example:
> + kexec_jump_back_entry=0x00000000000810d2
> +2) Following command sets the jump-back address for kexec.
> + kexec --load-jump-back-helper --entry=0x810d2
> +3) Jump to the system kernel
> + kexec -e
> Write Out the Dump File
More information about the kexec