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

[Andrew Morton]

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...)

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?