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

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Date:	Mon, 09 Feb 2015 12:22:04 +0900 (JST)
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	bhe@...hat.com
Cc:	ebiederm@...ssion.com, vgoyal@...hat.com,
	masami.hiramatsu.pt@...achi.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers"
 option issue in oops path

Hello,

From: Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path
Date: Mon, 9 Feb 2015 10:40:30 +0800

> On 02/05/15 at 05:59pm, 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@...fujitsu.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;
> 
> What if these two conditions !p->pid || is_global_init(p) are satisfied?
> Seems the behavious is changed.
> 

Please further follow do_exit() path. For each condition, there are
the corresponding panic() calls. In summary:

  oops_end
    1) panic() for in_interrupt()
    2) panic() for panic_on_oops
    do_exit
      3) panic() for !p->pid (idle task)
      exit_notify
        forget_original_parent
          find_child_reaper
            4) panic() for p->pid == 1 (init task)

--
Thanks.
HATAYAMA, Daisuke

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