linux-kernel - Re: [PATCHv2] MTD: Add UBI reboot notifier

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Date:	Fri, 12 Feb 2010 17:21:00 +0200
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Norbert van Bolhuis <nvbolhuis@...valley.nl>
Cc:	Kevin Cernekee <kpc.mtd@...il.com>, linux-mtd@...ts.infradead.org,
	dwmw2@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] MTD: Add UBI reboot notifier

On Fri, 2010-02-12 at 14:45 +0100, Norbert van Bolhuis wrote:
> Artem Bityutskiy wrote:
> > FYI, I do not like this patch, because it is not solving the problem, it
> > just makes the problem less likely. I.e., you are still screwed if you
> > reboot while some other task is doing erasure. Indeed, the background
> > thread is not the only task which may do erases.
> > 
> > I'm not going to revert this patch, but wanted to let you know that I
> > think it was my mistake to push it.
> > 
> 
> so, how to solve this properly ?
> 
> probably the only way is the reboot notifier of the MTD chip driver
> (for NOR flash only cmdset_0001 has one).

Well. UBI itself does not have problems with half-erased eraseblocks. As
the comment to the patch says, this is for a strange platform where the
boot loader panics when it encounters a half-erased EB.

So the most proper fix is to fix the boot-loader. Remember, a power cut
can introduce half-erased EBs, and you cannot address this in SW.

For clean reboots, you would need to have a reboot notifier in the MTD
lever, not in UBI. This notifier should:

1. Finish the current erase operation.
2. Prevent further erase operations.

The UBI patch is not a good solution.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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