Re: [PATCH 1/2] block: fail a short atomic bounce in bio_iov_iter_bounce_write()

[John Garry]

On 11/9/26 18:27, Tal Zussman wrote:
> > This looks reasonable, as atomic stable writes are implied to be
> > supported from 3373503df025a ("xfs: use bounce buffering direct I/O when
> > the device requires stable pages"). I am wondering how to test and prove
> > this (change is good and maintained)?
> I tested this with XFS on scsi_debug (dif=1 dix=1 atomic_wr=1), doing
> 1M RWF_ATOMIC direct writes and using fail_page_alloc to make the
> folio allocations in bio_alloc_bounce_folios() fail partway through.
> I had an LLM make it pretty precise and target bio_alloc_bounce_folios()
> using the stack filtering mechanism, so I don't think this necessarily
> makes sense as an xfstest if that's what you were thinking...
>
> Without this patch, the write returns -EINVAL and hits the
> WARN_ON_ONCE() in iomap_dio_bio_iter_one(). With it, the write returns
> -EINVAL without the warning.
>
> This also happened to turn up a scsi_debug bug: with dif=1 dix=1 it
> doesn't store the protection information for WRITE ATOMIC(16), so
> reading back an atomic write fails. I'll send a separate patch for that.

ok, I'll await the patch.

> Does that answer your question/is that what you were getting at?

Yes, this is ok. I am really just getting at whether we can add a test 
for this scenario.

Thanks,
John