Re: [BUG] iomap/io_uring: O_APPEND async buffered write silently re-appends a data chunk (corruption) on XFS, 6.1.y/6.12.y

[Brian Foster <bfoster@redhat.com>]

On Mon, Jun 08, 2026 at 01:17:10PM -0400, Eric Hagberg wrote:
> On Mon, Jun 8, 2026 at 12:03 PM Brian Foster <bfoster@redhat.com> wrote:
> > Another idea that came to mind is to try and just replace the -EAGAIN
> > return sequence from the low level iterator with a flag that triggers
> > -EAGAIN from the next iter advance. The idea here is to allow the write
> > to return partial completion (i.e. so no iov_iter revert) without having
> > to return an error from the lowest level in the stack. I had claude come
> > up with a quick patch [1] for reference/experimentation.
> >
> > This is based on v6.12 stable and compile tested only. It needs more
> > review and testing in general but might be worth throwing your
> > reproducer at if you can..?
> 
> With that patch applied, the reproducer runs clean - no errors - and
> gets roughly the same performance (maybe slightly better) as when run
> against a 6.18 kernel on the same VM.
> 

Thanks for testing. I'll look into some more regression testing of this
patch and try to clean it up and post it for proper review for stable.

Are you using the reproducer program in your original mail to test? If
so, does it require some concurrent memory pressure to reproduce, and
are you using anything in particular for that?

That test seems small enough that we could potentially include it in
fstests, though I'm still not so sure about the mem pressure part..
Since you guys wrote the test, any interest in porting into fstests? If
not I can look into it.

Brian

> Thanks,
> -Eric
>