linux-kernel - Re: [RESEND PATCH] kernel/panic/kexec: fix "crash_kexec_post

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Date:	Wed, 04 Mar 2015 20:46:40 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
CC:	ebiederm@...ssion.com, vgoyal@...hat.com,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	bhe@...hat.com, hidehiro.kawai.ez@...achi.com
Subject: Re: [RESEND PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers"
 option issue in oops path

(2015/03/04 17:56), 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().
> 

Thank you for fixing this issue :)

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

I think this is fundamentally needed, because crash_kexec (a.k.a.
kdump) is mainly for shooting bugs which cause kernel panic.
Thus, to avoid the scenario that something went wrong on kernel
panic and failed to get kdump, we have to call panic_notifiers
before that.

> Signed-off-by: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
> Acked-by: Baoquan He <bhe@...hat.com>
> Tested-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.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;
>  	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;
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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