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

[Christoph Hellwig <hch@lst.de>]

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.
> 
> To fix readahead as well, change iomap_readahead_iter to pass on
> iomap_readpage_iter return values less than or equal to zero.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>