powerpc/nvram: Fix an incorrect partition merge

[Michael Ellerman]

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.

cheers