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Date: Thu, 2 Dec 2010 10:46:49 +0100
From: Matthieu CASTET <matthieu.castet@parrot.com>
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Subject: Re: UBIFS partition on NOR flash not mountable after power cut test
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Cc: Anatolij Gustschin <agust@denx.de>,
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	Detlev Zundel <dzu@denx.de>
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Hi,

Artem Bityutskiy a écrit :
> On Wed, 2010-12-01 at 16:44 +0100, Anatolij Gustschin wrote:
>> On Wed, 1 Dec 2010 13:05:34 +0100
>> Anatolij Gustschin <agust@denx.de> wrote:
>> ... 
>>> My question is:
>>> Is it possible that the reset occured while running in
>>> nor_erase_prepare() just after clearing the VID header magic,
>>> but before clearing the EC header magic?
>> yes, it is possible and it seems this is the reason for
>> that next issue we've observed. Adding the call to the
>> machine restart callback in nor_erase_prepare() just before
>> clearing EC header magic to simulate this hypothetical case
>> we see:
> You are right, Anatoli.
> 
> Looking closer to my own code, I see that I treat PEB as
> "corrupted and should be preserved" if:
> 
> 1. EC header is OK.
> 2. VID header is corrupted.
> 3. data area is not "all 0xFFs".
> 
> And in 'nor_erase_prepare()' we first invalidate the VID header, and
> then invalidate the EC header. So there is a small window where you can
> end up with all 3 conditions to be true.
> 
> The solution is to first invalidate the EC header, and only then the VID
> header. Then in case of the race, we just lose the EC header, but VID
> header will be all-right, and UBI will handle this - it'll move the data
> from this PEB to another one, re-create EC header and use average EC
> count. But if you test this scenario, it will be great!!
> 
> This patch should help (compile-tested only).
> 
Shouldn't the correct solution will come with handling unstable page 
problem [1] ?

Matthieu

[1]
never trust a page where write/erase was interrupted.