Re: fix unintentional splitting of zone append bios

[Niklas Cassel <cassel@kernel.org>]

On Mon, Aug 26, 2024 at 07:37:53PM +0200, Christoph Hellwig wrote:
> Hi Jens,
> 
> this series fixes code that incorrectly splits of zoned append bios due
> to checking for a wrong max_sectors limit.  A big part of the cause is
> that the bio splitting code is a bit of a mess and full of landmines, so
> I fixed this as well.

Hello Christoph,

You say that this series fixes code that could affect every submitter of
zone append bios, thus I am a bit surprised to not see any Fixes-tag(s)
in any of the patches in this series. Was that intentional?

Even for a theoretical fix, doesn't this sound serious enough to warrant
zone append splits to be fixed in stable kernels as well?

When was this bug introduced? Or has it been broken since the support for
zone append was first added?


Kind regards,
Niklas


> 
> To hit this bug a submitter needs to submit a bio larger than max_sectors
> of device, but smaller than max_hw_sectors.  So far the only thing that
> reproduces it is my not yet upstream zoned XFS code, but in theory this
> could affect every submitter of zone append bios.
> 
> Diffstat:
>  block/blk-merge.c      |  162 ++++++++++++++++++++++---------------------------
>  block/blk-mq.c         |   11 +--
>  block/blk.h            |   70 +++++++++++++++------
>  fs/btrfs/bio.c         |   30 +++++----
>  include/linux/bio.h    |    4 -
>  include/linux/blkdev.h |    3 
>  6 files changed, 153 insertions(+), 127 deletions(-)