Re: ubi corrupted list not counted as bad block

[Richard Weinberger <richard.weinberger@xxxxxxxxx>]

On Wed, Nov 13, 2019 at 9:05 AM Balachandra KUMAR
<balachandra.kumar.ext@xxxxxxxxx> wrote:
>
> Hi MTD Experts,
>
>  I am hitting the below problem :
> UBI assert failed in ubi_wl_init at line 1632
> -> ubi_assert(ubi->good_peb_count == found_pebs);
>
> The issue is because, in the scan_peb( ) , a specific PEB is found to
> be corrupted in the volume header CRC calculation which is a
> UBI_IO_BAD_HDR error.

It is not just a CRC error. UBI found that the a volume header is bad *and*
follow up data is good. This must not happen.
Like the error message says, this needs manual inspection.

> Later in scan_peb ( ), my target hits the else part saying its an
> unexpected corruption.
> [attach.c]
> else if (!err)
>                         /* This corruption is caused by a power cut */
>                         err = add_to_list(ai, pnum, UBI_UNKNOWN,
>                                           UBI_UNKNOWN, ec, 1, &ai->erase);
>                 else {
>                         /* This is an unexpected corruption */
>                        err = add_corrupted(ai, pnum, ec);
>                  }

If you hit this code path you are already in deep trouble.
Data corrupted and UBI cannot say why.

> The count of good peb is done as below :
> /* code snippet in attach.c */
>    ubi->bad_peb_count = ai->bad_peb_count; (this is 0 in my case)
>    ubi->good_peb_count = ubi->peb_count - ubi->bad_peb_count;
> (total_peb_count(3464) - 0 = 3464) but what about the corrupted one?
>    ubi->corr_peb_count = ai->corr_peb_count;   (this is 1)
>
> Why is
> good_peb_count = peb_count - bad_peb_count ? (why not minus
> corrupt_peb_count or add it to erase list?)
>
> in the ubi_wl_init ( ) , the found_pebs is calculated from erase list
> and free list and we skip the corrupted peb list. But the good_count
> cotains the corrupted count as well.
> So , i hit this problem ->
>   ubi_assert(ubi->good_peb_count == found_pebs);
>
> What is the logic behind this good_peb_count?

It counts the good PEBs, as the name denotes.
But the key here is that "good" means anything which is not a bad block.

Corrupted PEBs are something in between. These are blocks which should
be good but aren't.

What is the value of accounting them? Like I said if you face this type of
error you lost already data and the upper layer (maybe UBIFS) is dead.

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-- 
Thanks,
//richard

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