Re: [5.15 REGRESSION v2] iomap: Fix inline extent handling in iomap_readpage

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On Tue, Nov 16, 2021 at 09:33:30PM -0800, Darrick J. Wong wrote:
> On Thu, Nov 11, 2021 at 05:17:14PM +0100, Andreas Gruenbacher wrote:
> > Before commit 740499c78408 ("iomap: fix the iomap_readpage_actor return
> > value for inline data"), when hitting an IOMAP_INLINE extent,
> > iomap_readpage_actor would report having read the entire page.  Since
> > then, it only reports having read the inline data (iomap->length).
> > 
> > This will force iomap_readpage into another iteration, and the
> > filesystem will report an unaligned hole after the IOMAP_INLINE extent.
> > But iomap_readpage_actor (now iomap_readpage_iter) isn't prepared to
> > deal with unaligned extents, it will get things wrong on filesystems
> > with a block size smaller than the page size, and we'll eventually run
> > into the following warning in iomap_iter_advance:
> > 
> >   WARN_ON_ONCE(iter->processed > iomap_length(iter));
> > 
> > Fix that by changing iomap_readpage_iter to return 0 when hitting an
> > inline extent; this will cause iomap_iter to stop immediately.
> 
> I guess this means that we also only support having inline data that
> ends at EOF?  IIRC this is true for the three(?) filesystems that have
> expressed any interest in inline data: yours, ext4, and erofs?

For erofs, confirmed. (also yes in the long run...)

Thanks,
Gao Xiang