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

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Wed, 6 May 2020 20:44:29 +0200 (CEST)
Richard Weinberger <richard@xxxxxx> wrote:

> Bean, Boris,
> 
> ----- Ursprüngliche Mail -----
> >> > 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.  
> 
> Uhh. Damaging just payload asks for trouble.

I'd expect UBI to just mark the LEB as bad and schedule it for erasure
(again, pretty similar to an interrupted erase).

> 
> >> > 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.  
> 
> Sadly it is not so easy.
> 
> IIRC the UBIFS log ring is such a corner case, it uses a fixed LEB range for
> this purpose. Before writing to a new LEB it unmaps it. If the resulting erase operation
> is interrupted before a new version of the same LEB is written reading from that
> LEB would result in ECC errors.

Duh. What happens when you have ECC errors? Does that stop the mount?
Shouldn't we make that part more robust?

>  
> > Would you please help us confirm this?  how does ubifs handle this situation?
> > Also other FS? Eg, jffs2, yaffs  
> 
> There are cases where (partially) erased LEBs are still referenced.
> UBIFS assumes that a LEB it unmaps is after a power-cut either 0xFF or intact.
> In relies in the fact that UBI will detect an interrupted erase operation and
> re-erases the PEB.
> Fastmap once violated this rule, it took years until the first user hit this.
> 
> So please make sure that the VID header will be destroyed.

I really hate the idea of having FS-specific logic in the Micron
quirk. Isn't there a way we can fix that in UBIFS? Plus, do we have any
guarantee that the EC/VID headers will be corrupted along with UBIFS
data when an erase is interrupted?

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