Re: [PATCH v4 0/6] BTT error clearing rework

Vishal Verma
2017-08-01T19:56:31Z

On 08/01, Kani, Toshimitsu wrote:
> On Tue, 2017-08-01 at 09:19 -0600, Toshi Kani wrote:
> > On Mon, 2017-07-31 at 23:35 +0000, Verma, Vishal L wrote:
> > > On Mon, 2017-07-31 at 23:15 +0000, Kani, Toshimitsu wrote:
> > > > On Wed, 2017-07-26 at 17:35 -0600, Vishal Verma wrote:
> :
> > > Thanks for the test Toshi, I will try and reproduce it.
> > > My first guess is - are the injected errors potentially in the BTT
> > > metadata area towards the end?
> > >
> > > ->rw_bytes can only clear errors on properly aligned writes, and
> > > the btt metadata writes will be too small to clear metadata
> > > errors..
> >
> > I picked an injected offset without careful thoughts, so it is
> > possible that I might have stepped into such area. I just tested
> > with a block device interface with multiple different offsets, and
> > they failed in clearing as well... I will look into further as well
> > as my test setup.
>
> The change/hack below takes care of the issue in my setup. There is a
> discrepancy in offset between the pre-check in btt_write_pg() and the
> actual check in nsio_rw_bytes().
>
> Thanks,
> -Toshi
>
> ---
> drivers/nvdimm/btt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
> index 8a959f8..83ad4c6 100644
> --- a/drivers/nvdimm/btt.c
> +++ b/drivers/nvdimm/btt.c
> @@ -1137,7 +1137,7 @@ static bool btt_is_badblock(struct btt *btt,
> struct arena_info *arena,
> u32 postmap)
> {
> u64 nsoff = to_namespace_offset(arena, postmap);
> - sector_t phys_sector = nsoff >> 9;
> + sector_t phys_sector = (nsoff + arena->nd_btt->initial_offset) >> 9;
>
> return is_bad_pmem(btt->phys_bb, phys_sector, arena->internal_lbasize);
> }

Hey Toshi, that is a great catch (I'm going to look at enhancing the
unit tests too to catch this).

Your patch is correct. Normally whenever we calculate a 'nsoff', we use
that to do arena_{read,write}_bytes, and that takes care of adding the
initial_offset. This was the first instance where we calculated nsoff
and did something other than rw_bytes with it (i.e. is_bad_pmem), and
therefore this nsoff needs the initial_offset adjustment manually..

However just adding that here is inviting future bugs like this, so I'm
going to refactor the initial_offset adjustment into some helpers and
use those across the board. That should prevent this sort of a bug
again.

Thanks for the report and the root cause!

-Vishal