Re: [RESEND PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Mar 04, 2015 at 05:56:48PM +0900, HATAYAMA Daisuke wrote:
> The commit f06e5153f4ae2e2f3b0300f0e260e40cb7fefd45 introduced
> "crash_kexec_post_notifiers" kernel boot option, which toggles
> wheather panic() calls crash_kexec() before or after panic_notifiers
> and dump kmsg.
> 
> The problem is that the commit overlooks panic_on_oops kernel boot
> option. If it is enabled, crash_kexec() is called directly without
> going through panic() in oops path.
> 
> To fix this issue, this patch adds a check to
> "crash_kexec_post_notifiers" in the condition of kexec_should_crash().
> 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> Acked-by: Baoquan He <bhe@redhat.com>
> Tested-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
> ---
>  include/linux/kernel.h | 3 +++
>  kernel/kexec.c         | 2 ++
>  kernel/panic.c         | 2 +-
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 64ce58b..f47379f 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -426,6 +426,9 @@ extern int panic_on_unrecovered_nmi;
>  extern int panic_on_io_nmi;
>  extern int panic_on_warn;
>  extern int sysctl_panic_on_stackoverflow;
> +
> +extern bool crash_kexec_post_notifiers;
> +
>  /*
>   * Only to be used by arch init code. If the user over-wrote the default
>   * CONFIG_PANIC_TIMEOUT, honor it.
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 9a8a01a..0ecf252 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -84,6 +84,8 @@ struct resource crashk_low_res = {
>  
>  int kexec_should_crash(struct task_struct *p)
>  {
> +	if (crash_kexec_post_notifiers)
> +		return 0;

This is little confusing. So if crash_kexec_post_notifiers is set but
panic_on_oops is not set, still we will return?

Should we do this only if panic_on_oops is set? IOW, how about following

	if (panic_on_oops && crash_kexec_post_notifiers)
		return 0;

And then also put a comment explaining the rationale.

Thanks
Vivek

>  	if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
>  		return 1;
>  	return 0;
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 4d8d6f9..6582546 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -32,7 +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 crash_kexec_post_notifiers;
> +bool crash_kexec_post_notifiers;
>  int panic_on_warn __read_mostly;
>  
>  int panic_timeout = CONFIG_PANIC_TIMEOUT;
> -- 
> 1.9.3
>