iomap: fix inline data on buffered read

Previously, iomap_readpage_iter() returning 0 would break out of the
loops of iomap_readahead_iter(), which is what iomap_read_inline_data()
relies on.

However, commit d9dc477 ("iomap: advance the iter directly on
buffered read") changes this behavior without calling
iomap_iter_advance(), which causes EROFS to get stuck in
iomap_readpage_iter().

It seems iomap_iter_advance() cannot be called in
iomap_read_inline_data() because of the iomap_write_begin() path, so
handle this in iomap_readpage_iter() instead.

Reported-and-tested-by: Bo Liu <liubo03@inspur.com>
Fixes: d9dc477 ("iomap: advance the iter directly on buffered read")
Cc: Brian Foster <bfoster@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250319085125.4039368-1-hsiangkao@linux.alibaba.com
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: hsiangkao

fs/iomap/buffered-io.c

@@ -372,9 +372,14 @@ static int iomap_readpage_iter(struct iomap_iter *iter,
 	struct iomap_folio_state *ifs;
 	size_t poff, plen;
 	sector_t sector;
+	int ret;
 
-	if (iomap->type == IOMAP_INLINE)
-		return iomap_read_inline_data(iter, folio);
+	if (iomap->type == IOMAP_INLINE) {
+		ret = iomap_read_inline_data(iter, folio);
+		if (ret)
+			return ret;
+		return iomap_iter_advance(iter, &length);
+	}
 
 	/* zero post-eof blocks as the page may be mapped */
 	ifs = ifs_alloc(iter->inode, folio, iter->flags);