Re: [PATCH v6] iomap: support tail packing inline read

Matthew Wilcox
2021-07-23T15:57:11Z

On Fri, Jul 23, 2021 at 11:23:38PM +0800, Gao Xiang wrote:
> Hi Matthew,
>
> On Fri, Jul 23, 2021 at 04:05:29PM +0100, Matthew Wilcox wrote:
> > On Thu, Jul 22, 2021 at 07:39:47AM +0200, Christoph Hellwig wrote:
> > > @@ -675,7 +676,7 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,
> > >
> > > flush_dcache_page(page);
> > > addr = kmap_atomic(page);
> > > - memcpy(iomap->inline_data + pos, addr + pos, copied);
> > > + memcpy(iomap_inline_buf(iomap, pos), addr + pos, copied);
> >
> > This is wrong; pos can be > PAGE_SIZE, so this needs to be
> > addr + offset_in_page(pos).
>
> Yeah, thanks for pointing out. It seems so, since EROFS cannot test
> such write path, previously it was disabled explicitly. I could
> update it in the next version as above.

We're also missing a call to __set_page_dirty_nobuffers(). This
matters to nobody right now -- erofs is read-only and gfs2 only
supports inline data in the inode. I presume what is happening
for gfs2 is that at inode writeback time, it copies the ~60 bytes
from the page cache into the inode and then schedules the inode
for writeback.

But logically, we should mark the page as dirty. It'll be marked
as dirty by ->mkwrite, should the page be mmaped, so gfs2 must
already cope with a dirty page for inline data.