On Mon, Apr 14, 2014 at 01:51:58PM +0900, Masami Hiramatsu wrote:
> Add a "late_kdump" option to run kdump after running panic
> notifiers and dump kmsg. This can help rare situations which
> kdump drops in failure because of unstable crashed kernel
> or hardware failure (memory corruption on critical data/code),
> or the 2nd kernel is broken by the 1st kernel (it's a broken
> behavior, but who can guarantee that the "crashed" kernel
> works correctly?).
>
> Usage: add "late_kdump" to kernel boot option. That's all.
>
> Note that this actually increases risks of the failure of
> kdump. This option should be set only if you worry about
> the rare case of kdump failure rather than increasing the
> chance of success.
>
Masami,
So what's the alternative to kdump which is more reliable? IOW, what
action you are planning to take through kmsg_dump() or through
panic_notifiers?
I have seen that many a times developers have tried to make the case
to save kernel buffers to NVRAM. Does it work well? Has it been proven
to be more reliable than kdump?
Thanks
Vivek
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
> Cc: Eric Biederman <ebied...@xmission.com>
> Cc: Vivek Goyal <vgo...@redhat.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Yoshihiro YUNOMAE <yoshihiro.yunomae...@hitachi.com>
> Cc: Satoru MORIYA <satoru.moriya...@hitachi.com>
> Cc: Motohiro Kosaki <motohiro.kos...@us.fujitsu.com>
> Cc: Takenori Nagano <t-nag...@ah.jp.nec.com>
> ---
> Documentation/kernel-parameters.txt | 7 +++++++
> kernel/panic.c | 24 ++++++++++++++++++++++--
> 2 files changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index 03e50b4..1ba58da 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2339,6 +2339,13 @@ bytes respectively. Such letter suffixes can also be
> entirely omitted.
> timeout < 0: reboot immediately
> Format: <timeout>
>
> + late_kdump Run kdump after running panic-notifiers and dumping
> + kmsg. This only for the users who doubt kdump always
> + succeeds in any situation.
> + Note that this also increases risks of kdump failure,
> + because some panic notifiers can make the crashed
> + kernel more unstable.
> +
> parkbd.port= [HW] Parallel port number the keyboard adapter is
> connected to, default is 0.
> Format: <parport#>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index d02fa9f..bba42b5 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -32,6 +32,7 @@ static unsigned long tainted_mask;
> static int pause_on_oops;
> static int pause_on_oops_flag;
> static DEFINE_SPINLOCK(pause_on_oops_lock);
> +static bool late_kdump;
>
> int panic_timeout = CONFIG_PANIC_TIMEOUT;
> EXPORT_SYMBOL_GPL(panic_timeout);
> @@ -112,9 +113,14 @@ void panic(const char *fmt, ...)
> /*
> * If we have crashed and we have a crash kernel loaded let it handle
> * everything else.
> - * Do we want to call this before we try to display a message?
> + * If we want to call this after we try to display a message, pass
> + * the "late_kdump" option to the kernel.
> */
> - crash_kexec(NULL);
> + if (!late_kdump)
> + crash_kexec(NULL);
> + else
> + pr_emerg("Warning: late_kdump option is set. Please DO NOT "
> + "report bugs about kdump failure with this option.\n");
>
> /*
> * Note smp_send_stop is the usual smp shutdown function, which
> @@ -131,6 +137,13 @@ void panic(const char *fmt, ...)
>
> kmsg_dump(KMSG_DUMP_PANIC);
>
> + /*
> + * If you doubt kdump always works perfectly in any situation,
> + * "late_kdump" offers you to try kdump after running panic_notifier
> + * and dumping kmsg.
> + */
> + crash_kexec(NULL);
> +
> bust_spinlocks(0);
>
> if (!panic_blink)
> @@ -472,6 +485,13 @@ EXPORT_SYMBOL(__stack_chk_fail);
> core_param(panic, panic_timeout, int, 0644);
> core_param(pause_on_oops, pause_on_oops, int, 0644);
>
> +static int __init setup_late_kdump(char *s)
> +{
> + late_kdump = true;
> + return 0;
> +}
> +early_param("late_kdump", setup_late_kdump);
> +
> static int __init oops_setup(char *s)
> {
> if (!s)
>
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