From: Baokun Li <libaokun1@huawei.com>

In ext4_readdir(), page_cache_sync_readahead() is used to readahead mapped
physical blocks. With LBS support, this can lead to a negative right shift.

To fix this, the page index is now calculated by first converting the
physical block number (pblk) to a file position (pos) before converting
it to a page index. Also, the correct number of pages to readahead is now
passed.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
---
 fs/ext4/dir.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index d4164c507a90..256fe2c1d4c1 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -192,13 +192,13 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 			continue;
 		}
 		if (err > 0) {
-			pgoff_t index = map.m_pblk >>
-					(PAGE_SHIFT - inode->i_blkbits);
+			pgoff_t index = map.m_pblk << inode->i_blkbits >>
+					PAGE_SHIFT;
 			if (!ra_has_index(&file->f_ra, index))
 				page_cache_sync_readahead(
 					sb->s_bdev->bd_mapping,
-					&file->f_ra, file,
-					index, 1);
+					&file->f_ra, file, index,
+					1 << EXT4_SB(sb)->s_min_folio_order);
 			file->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT;
 			bh = ext4_bread(NULL, inode, map.m_lblk, 0);
 			if (IS_ERR(bh)) {
-- 
2.46.1