[PATCH -next] mm/filemap: fix that first page is not mark accessed in filemap_read()

[Yu Kuai]

In filemap_read(), 'ra->prev_pos' is set to 'iocb->ki_pos + copied',
while it should be 'iocb->ki_ops'. For consequence,
folio_mark_accessed() will not be called for 'fbatch.folios[0]' since
'iocb->ki_pos' is always equal to 'ra->prev_pos'.

Fixes: 06c0444290ce ("mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 mm/filemap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 9daeaab36081..0b776e504d35 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2728,10 +2728,11 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
 				flush_dcache_folio(folio);
 
 			copied = copy_folio_to_iter(folio, offset, bytes, iter);
-
-			already_read += copied;
-			iocb->ki_pos += copied;
-			ra->prev_pos = iocb->ki_pos;
+			if (copied) {
+				ra->prev_pos = iocb->ki_pos;
+				already_read += copied;
+				iocb->ki_pos += copied;
+			}
 
 			if (copied < bytes) {
 				error = -EFAULT;
-- 
2.31.1