Re: [PATCH AUTOSEL 5.9 089/147] dm: change max_io_len() to use blk_max_size_offset()

[Sasha Levin]

On Tue, Oct 27, 2020 at 08:19:59AM -0400, Mike Snitzer wrote:
> On Mon, Oct 26 2020 at  7:48pm -0400,
> Sasha Levin <sashal@xxxxxxxxxx> wrote:
>
> > From: Mike Snitzer <snitzer@xxxxxxxxxx>
> >
> > [ Upstream commit 5091cdec56faeaefa79de4b6cb3c3c55e50d1ac3 ]
> >
> > Using blk_max_size_offset() enables DM core's splitting to impose
> > ti->max_io_len (via q->limits.chunk_sectors) and also fallback to
> > respecting q->limits.max_sectors if chunk_sectors isn't set.
> >
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> Not sure why this commit elevated to stable@ picking it up, please
> explain.

I misread the series this patch was in as being a fix rather than only
the first patch, sorry :(

> But you cannot take this commit standalone. These commits are prereqs:
>
> 22ada802ede8 block: use lcm_not_zero() when stacking chunk_sectors
> 07d098e6bbad block: allow 'chunk_sectors' to be non-power-of-2
> 882ec4e609c1 dm table: stack 'chunk_sectors' limit to account for target-specific splitting
>
> This goes for all stable@ trees you AUTOSEL'd commit 5091cdec56f for.
>
> Mike
>
> > ---
> >  drivers/md/dm.c | 20 ++++++++------------
> >  1 file changed, 8 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> > index 6ed05ca65a0f8..3982012b1309c 100644
> > --- a/drivers/md/dm.c
> > +++ b/drivers/md/dm.c
> > @@ -1051,22 +1051,18 @@ static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti
> >  static sector_t max_io_len(sector_t sector, struct dm_target *ti)
> >  {
> >  	sector_t len = max_io_len_target_boundary(sector, ti);
> > -	sector_t offset, max_len;
> > +	sector_t max_len;
> >
> >  	/*
> >  	 * Does the target need to split even further?
> > +	 * - q->limits.chunk_sectors reflects ti->max_io_len so
> > +	 *   blk_max_size_offset() provides required splitting.
> > +	 * - blk_max_size_offset() also respects q->limits.max_sectors
> >  	 */
> > -	if (ti->max_io_len) {
> > -		offset = dm_target_offset(ti, sector);
> > -		if (unlikely(ti->max_io_len & (ti->max_io_len - 1)))
> > -			max_len = sector_div(offset, ti->max_io_len);
> > -		else
> > -			max_len = offset & (ti->max_io_len - 1);
> > -		max_len = ti->max_io_len - max_len;
> > -
> > -		if (len > max_len)
> > -			len = max_len;
> > -	}
> > +	max_len = blk_max_size_offset(dm_table_get_md(ti->table)->queue,
> > +				      dm_target_offset(ti, sector));
> > +	if (len > max_len)
> > +		len = max_len;
> >
> >  	return len;
> >  }
> > --
> > 2.25.1

--
Thanks,
Sasha