powerpc/nvram: Fix an incorrect partition merge

[xinhui]

On 2016年06月07日 19:39, Michael Ellerman wrote:
> On Mon, 2016-06-06 at 13:31 +0800, xinhui wrote:
>> On 2016年06月03日 19:47, Michael Ellerman wrote:
>>> On Thu, 2015-10-12 at 07:30:02 UTC, xinhui wrote:
>>>> From: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
>>>>
>>>> When we merge two contiguous partitions whose signatures are marked
>>>> NVRAM_SIG_FREE, We need update prev's length and checksum, then write it
>>>> to nvram, not cur's. So lets fix this mistake now.
>>>>
>>>> Also use memset instead of strncpy to set the partition's name. It's
>>>> more readable if we want to fill up with duplicate chars .
>>>
>>> Does this ever happen in practice? ie. should we backport the fix to stable
>>> kernels?
>>
>> I did not see that nvram warning in practice. BUT I suggest to backport it to stable kernel. :)
>>
>> Let me recall the story. :)
>> In past days, I was using pstore to keep some kernel logs. and sometimes I found my own logs and the panic logs did not show.
>> pstore use a fixed-address reserved memory In x86 while nvram instead in ppc.
>>
>> Then I spent some days to review the nvram codes.
>> And worked out three patches to fix all issues that I found in nvram. BUT looks like I only sent out two of them. :)
>> I lost the third patch maybe...
>
> OK.
>
>>> Has it always been broken?
>>
>> no. after nvram partition corruption hit, all nvram partitions will be erased and re-alloc after the second machine reboot.
>> I don't know who does it but i guess it is the firmware. :)
>
> Actually I meant has the code always contained the bug, or was it added recently.
>
fix fa2b4e54d41f3c9f1bee6a7d63ecd4f0ab161e89 ("powerpc/nvram: Improve partition removal")
and it is from Ben.

So cc Ben :)
> cheers
>