Re: [PATCH 1/5] zram: handle multiple pages attached bio's bvec

[Minchan Kim]

Hi Andrew,

On Mon, Apr 03, 2017 at 03:45:28PM -0700, Andrew Morton wrote:
> On Mon, 3 Apr 2017 14:17:29 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> 
> > Johannes Thumshirn reported system goes the panic when using NVMe over
> > Fabrics loopback target with zram.
> > 
> > The reason is zram expects each bvec in bio contains a single page
> > but nvme can attach a huge bulk of pages attached to the bio's bvec
> > so that zram's index arithmetic could be wrong so that out-of-bound
> > access makes panic.
> > 
> > It can be solved by limiting max_sectors with SECTORS_PER_PAGE like
> > [1] but it makes zram slow because bio should split with each pages
> > so this patch makes zram aware of multiple pages in a bvec so it
> > could solve without any regression.
> > 
> > [1] 0bc315381fe9, zram: set physical queue limits to avoid array out of
> >     bounds accesses
> 
> This isn't a cleanup - it fixes a panic (or is it a BUG or is it an
> oops, or...)

I should have written more carefully.
Johannes reported the problem with fix[1] and Jens already sent it to the
mainline to fix it. However, during the discussion, we can solve the problem
nice way so this is revert of [1] plus solving the problem with other way
which no need to split bio.

Thanks.

> 
> How serious is this bug?  Should the fix be backported into -stable
> kernels?  etc.
> 
> A better description of the bug's behaviour would be appropriate.
> 
> > Cc: Jens Axboe <axboe@xxxxxxxxx>
> > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > Reported-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > Tested-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> 
> This signoff trail is confusing.  It somewhat implies that Johannes
> authored the patch which I don't think is the case?
> 
>