linux-kernel - Re: [PATCH v2] ramoops: use pstore interface

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Date:	Fri, 2 Dec 2011 11:19:50 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Marco Stornelli <marco.stornelli@...il.com>
Cc:	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...il.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] ramoops: use pstore interface

On Fri, Dec 2, 2011 at 12:20 AM, Marco Stornelli
<marco.stornelli@...il.com> wrote:
> Il 02/12/2011 03:40, Chen Gong ha scritto:
>
>> 于 2011/12/1 18:31, Marco Stornelli 写道:
>>>
>>> Il 29/11/2011 18:24, Kees Cook ha scritto:
>>>>
>>>> On Mon, Nov 28, 2011 at 8:50 PM, Chen Gong<gong.chen@...ux.intel.com>
>>>> wrote:
>>>>>
>>>>> 于 2011/11/29 4:09, Kees Cook 写道:
>>>>>>
>>>>>>
>>>>>> Instead of using /dev/mem directly, use the common pstore
>>>>>> infrastructure
>>>>>> to handle Oops gathering and extraction.
>>>>>>
>>>>>> Signed-off-by: Kees Cook<keescook@...omium.org>
>>>>>> ---
>>>>>> This depends on the pstore changes waiting for -next in:
>>>>>>
>>>>>>
>>>>>> http://git.kernel.org/?p=linux/kernel/git/aegl/linux.git;a=shortlog;h=refs/heads/next
>>>>>>
>>>>>>
>>>>>> ---
>>>>>> Documentation/ramoops.txt | 8 +-
>>>>>> drivers/char/Kconfig | 1 +
>>>>>> drivers/char/ramoops.c | 206
>>>>>> ++++++++++++++++++++++++++++++++++-----------
>>>>>> 3 files changed, 160 insertions(+), 55 deletions(-)
>>>>>>
>>>>>> diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
>>>>>> index 8fb1ba7..a0b9d8e 100644
>>>>>> --- a/Documentation/ramoops.txt
>>>>>> +++ b/Documentation/ramoops.txt
>>>>>> @@ -3,7 +3,7 @@ Ramoops oops/panic logger
>>>>>>
>>>>>> Sergiu Iordache<sergiu@...omium.org>
>>>>>>
>>>>>> -Updated: 8 August 2011
>>>>>> +Updated: 17 November 2011
>>>>>>
>>>>>> 0. Introduction
>>>>>>
>>>>>> @@ -71,6 +71,6 @@ timestamp and a new line. The dump then continues
>>>>>> with
>>>>>> the actual data.
>>>>>>
>>>>>> 4. Reading the data
>>>>>>
>>>>>> -The dump data can be read from memory (through /dev/mem or other
>>>>>> means).
>>>>>> -Getting the module parameters, which are needed in order to parse the
>>>>>> data, can
>>>>>> -be done through /sys/module/ramoops/parameters/* .
>>>>>> +The dump data can be read from the pstore filesystem. The format for
>>>>>> these
>>>>>> +files is "dmesg-ramoops-N", where N is the record number in
>>>>>> memory. To
>>>>>> delete
>>>>>> +a stored record from RAM, simply unlink the respective pstore file.
>>>>>
>>>>>
>>>>> I think the definition of "mem_address" in the doc is not very
>>>>> clear. It is
>>>>> not a normal memory instead of a persistent RAM. I suggest adding more
>>>>> descriptions.
>>>>> It's better if there is a real example.
>>>>
>>>> Okay. I'm not sure it's in the scope of this patch, but I can try.
>>>>
>>>> Marco, do you have suggestions for how this could be enhanced?
>>>
>>> I don't know actually. It's not mandatory use a persistent memory. A
>>> simple
>>> piece of reserved RAM is ok. Obviously it will work only over reboot
>>> and not
>>> over power down. I define mem_address as a generic piece of reserved
>>> memory.
>>
>> Anyway, we need a pratical exmaple to instruct us how to use this diver.
>
> For example we can use the mem parameter to reserve memory and use it as
> ramoops buffer, very simple.

I tried both "mem" and "memmap":

mem=0x3f000000 ramoops.mem_address=0x3f000000 ramoops.mem_size=0x40000
ramoops.record_size=0x10000

memmap=256K$0x3f000000 ramoops.mem_address=0x3f000000
ramoops.mem_size=0x40000 ramoops.record_size=0x10000

Neither works for me (I end up triggering a panic via BUG in kfree). I
wonder if it's some bad interaction between the cmdline and the memory
tables? When I boot with mem=0x3f000000 and without ramoops, I see in
/proc/iomem:

00100000-3effffff : System RAM
  01000000-0137c35f : Kernel code
  0137c360-0151e85f : Kernel data
  01591000-01627fff : Kernel bss
3f000000-3fffcfff : RAM buffer

It seems like the system isn't ignoring the region? What's the right
way to do this?

-Kees

-- 
Kees Cook
ChromeOS Security
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