[PATCH] mm: fix blkdev size calculation in generic_write_checks

[Dmitry Monakhov <dmonakhov@openvz.org>]

Currently block device size calculated regardless its
bd_block_size. This may result attempt to write outside
block device if i_size not aligned to bdev->bd_block_size
and result in EIO.

#### TEST_CASE_BEGIN
# fdisk -l /dev/sdc
Disk /dev/sdc: 36.7 GB, 36703918080 bytes
255 heads, 63 sectors/track, 4462 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1         254     2040223+  83  Ldinux
/dev/sdc2             255         379     1004062+  83  Linux
####
#### /dev/sdc2 size not aligned to 4K

#### at this time bd_block_size == 512 so generic_write_check
#### performed correctly
# dd if=/dev/zero of=/dev/sdc2 bs=1k count=7 seek=1004058
dd: writing `/dev/sdc2': No space left on device
5+0 records in
4+0 records out

#### this bdev contain ext4fs with blksize = 4K
# mount /dev/sdc2 /mnt/
#### after we mounted this bdev bd_block_size == fsblksize == 4K

#### the same write operation failed with EIO
# dd if=/dev/zero of=/dev/sdc2 bs=1k count=7 seek=1004058
dd: writing `/dev/sdc2': Input/output error
3+0 records in
2+0 records out
#### Attempt to write whole fsblock result write access outside
#### blkdevice and cause -EIO (returned by blkdev_get_block)
#### TEST_CASE_END

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 mm/filemap.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 2c8776b..a23ee8a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1867,9 +1867,11 @@ inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, i
 	} else {
 #ifdef CONFIG_BLOCK
 		loff_t isize;
+		unsigned int blksize;
 		if (bdev_read_only(I_BDEV(inode)))
 			return -EPERM;
-		isize = i_size_read(inode);
+		blksize = block_size(I_BDEV(inode));
+		isize = i_size_read(inode) & ~(blksize - 1);
 		if (*pos >= isize) {
 			if (*count || *pos > isize)
 				return -ENOSPC;
-- 
1.5.2.2