linux-kernel - Re: [PATCH] kernel/panic: Add "late_kdump" option for kdump in unstable condition

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Date:	Thu, 17 Apr 2014 10:59:14 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Satoru MORIYA <satoru.moriya.br@...achi.com>,
	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>,
	Takenori Nagano <t-nagano@...jp.nec.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Motohiro Kosaki <Motohiro.Kosaki@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kernel/panic: Add "late_kdump" option for kdump in unstable
 condition

Thank you for review!

(2014/04/16 22:48), Vivek Goyal wrote:
> 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.
>>
>> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>> Cc: Eric Biederman <ebiederm@...ssion.com>
>> Cc: Vivek Goyal <vgoyal@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
>> Cc: Satoru MORIYA <satoru.moriya.br@...achi.com>
>> Cc: Motohiro Kosaki <Motohiro.Kosaki@...fujitsu.com>
>> Cc: Takenori Nagano <t-nagano@...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.
>> +
> 
> I am wondering if "crash_kexec_post_notifiers" will be a better name
> to represent what we are trying to do here.

OK, I'll rename that.

> 
>>  	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");
> 
> I think above message about DO NOT report bugs seems unnecessary. 

OK, so I just notify the option is set as below.
"Warning: crash_kexec_post_notifiers is set.\n"

Thank you again!

-- 
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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