On Tue, Apr 09, 2024 at 03:57:58PM +0200, Christoph Hellwig wrote:
> On Mon, Apr 08, 2024 at 05:48:02PM +0800, Ming Lei wrote:
> > The limit is from commit 09324d32d2a0 ("block: force an unlimited segment
> > size on queues with a virt boundary") which claims to fix f6970f83ef79
> > ("block: don't check if adjacent bvecs in one bio can be mergeable").
> >
> > However commit f6970f83ef79 only covers merge code which isn't used by
> > bio driver at all, so not sure pre-6.9-rc is broken for stacking driver.
>
> We can stack rq drivers as well.
>
> > Also commit 09324d32d2a0 mentioned that it did not cause problem,
> > actually 64K default segment size limits always exists even though the
> > device doesn't provide one, so looks there isn't report as 'real bugs',
> > or maybe I miss something?
>
> The problem is when the segment size does not align to the boundary
> mask as you'll now start feeding malformed segments/entris to the
> device.
In case of single bio, this bio will be split with max segment size
if segment size doesn't align with virt boundary, so the resulted bio
is still valid because virt-boundary allows the last bvec to be
unaligned.
In case of bio merge, bio_will_gap() is always called to make sure
there isn't gap between the two bios wrt. virt boundary.
Can you explain a bit how one malformed bio is made?
Thanks,
Ming
