Subject: [PATCH] do_direct_IO: Use inode->i_blkbits to compute block count to be cleaned

From: Chandan Rajendra <[email-masked]>
Date: Sun, 8 Jan 2017 20:17:10 +0530

The code currently uses sdio->blkbits to compute the number of blocks to
be cleaned. However sdio->blkbits is derived from the logical block size
of the underlying block device (Refer to the definition of
do_blockdev_direct_IO()). Due to this, generic/299 test would rarely
fail when executed on an ext4 filesystem with 64k as the block size and
when using a virtio based disk (having 512 byte as the logical block
size) inside a kvm guest.

This commit fixes the bug by using inode->i_blkbits to compute the
number of blocks to be cleaned.

Signed-off-by: Chandan Rajendra <[email-masked]>
---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index aeae8c0..b20adf9 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -905,6 +905,7 @@ static inline void dio_zero_block(struct dio *dio, struct dio_submit *sdio,
 static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
 			struct buffer_head *map_bh)
 {
+	const unsigned i_blkbits = dio->inode->i_blkbits;
 	const unsigned blkbits = sdio->blkbits;
 	int ret = 0;
 
@@ -949,7 +950,7 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
 					clean_bdev_aliases(
 						map_bh->b_bdev,
 						map_bh->b_blocknr,
-						map_bh->b_size >> blkbits);
+						map_bh->b_size >> i_blkbits);
 				}
 
 				if (!sdio->blkfactor)
-- 
2.5.5