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

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Date:	Tue, 10 Feb 2015 17:32:17 +0900
From:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	Baoquan He <bhe@...hat.com>, 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,

(2015/02/09 12:29), Baoquan He wrote:> On 02/09/15 at 12:22pm, HATAYAMA Daisuke wrote:
>> From: Baoquan He <bhe@...hat.com>
>>> On 02/05/15 at 05:59pm, HATAYAMA Daisuke wrote:
>>>> 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)
> 
> Yes, all conditions have been covered.
> 
> So this patch is necessary, ACK it. Thanks
> 
> Acked-by: Baoquan He <bhe@...hat.com>

Thanks for the patch!
I tested it in following cases on x86_64 and it worked well;
my panic notifier was called, then 2nd kernel booted.

- Null pointer dereference in each context of
  - hard IRQ
  - pid == 0
  - pid == 1
  - others with panic_on_oops=1
- Zero-divide in the context of normal process
  (panic_on_oops=1)

Tested-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>

-- 
Hidehiro Kawai
Hitachi, Yokohama Research Laboratory


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