Re: [EXT] [PATCH v2 3/3] mtd: rawnand: micron: Address the shallow erase issue

From: Boris Brezillon <boris.brezillon@collabora.com>
To: "Bean Huo (beanhuo)" <beanhuo@micron.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <Tudor.Ambarus@microchip.com>,
	Richard Weinberger <richard@nod.at>,
	Steve deRosier <derosier@gmail.com>,
	"Zoltan Szubbocsev \(zszubbocsev\)" <zszubbocsev@micron.com>,
	"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	Piotr Wojtaszczyk <WojtaszczykP@cumminsallison.com>
Subject: Re: [EXT] [PATCH v2 3/3] mtd: rawnand: micron: Address the shallow erase issue
Date: Wed, 6 May 2020 18:29:10 +0200	[thread overview]
Message-ID: <20200506182910.6a9863bd@collabora.com> (raw)
In-Reply-To: <BN7PR08MB56843895500F4ADA88262C59DBA40@BN7PR08MB5684.namprd08.prod.outlook.com>

On Wed, 6 May 2020 16:09:19 +0000
"Bean Huo (beanhuo)" <beanhuo@micron.com> wrote:

> Hi, Richard
> 
> > > > > > +	}  
> > > > >
> > > > >
> > > > > Here, if the power loss happens before erasing this block, for the
> > > > > next time boot up, What will happen from FS layer in case FS
> > > > > detect this filled  
> > > > data?
> > > >
> > > > Most likely ECC errors will be returned, but that doesn't matter
> > > > since this block was about to be erased. You have pretty much the
> > > > same problem for partially erase blocks already, and that should be
> > > > handled by the wear-leveling/FS, if not, that would be bug (note
> > > > that it's properly handled by UBI, which just considers the block as invalid and  
> > schedules an erase).  
> > > >  
> > >
> > > Concerning this, I still have question, for the UBIFS,  If I am
> > > correct, there are EC and VID header both being damaged, then UBIFS
> > > will re-erase it. I don't know if UBIFS can handle there is dirty/filling data in the  
> > some pages  and EC/VID valid.  
> > > Maybe Richard has fixed it.  
> > 
> > If the block is being erased that means there's another one mapped to the same
> > LEB, or the block is simply not needed anymore. In both cases, this old block
> > shouldn't be referenced. Again, if that happens, it's a bug.  
> 
> Would you please help us confirm this?  how does ubifs handle this situation? Also other FS? Eg, jffs2, yaffs
> 

And if you're really worried about that, forcibly writing all pages
starting from 0 should do the trick. But I don't think that's needed.
As I said, when you trigger an erase, you're not guaranteed the erase
will complete before a potential power-cut, meaning that part of your
data might still be valid, while others could be corrupted.

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