[PATCH 4/4] ext4: serialize truncate with owerwrite DIO workers

[Dmitry Monakhov <dmonakhov@openvz.org>]

Jan Kara have spotted interesting issue:
There are  potential data corruption issue with  direct IO overwrites
racing with truncate:
 Like:
  dio write                      truncate_task
  ->ext4_ext_direct_IO
   ->overwrite == 1
    ->down_read(&EXT4_I(inode)->i_data_sem);
    ->mutex_unlock(&inode->i_mutex);
                               ->ext4_setattr()
                                ->inode_dio_wait()
                                ->truncate_setsize()
                                ->ext4_truncate()
                                 ->down_write(&EXT4_I(inode)->i_data_sem);
    ->__blockdev_direct_IO
     ->ext4_get_block
     ->submit_io()
    ->up_read(&EXT4_I(inode)->i_data_sem);
                                 # truncate data blocks, allocate them to
                                 # other inode - bad stuff happens because
                                 # dio is still in flight.

In order to serialize with truncate dio worker should grab extra i_dio_count
reference before drop i_mutex.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 fs/ext4/inode.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 5a75908..9725acb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3035,6 +3035,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 		overwrite = *((int *)iocb->private);
 
 		if (overwrite) {
+			atomic_inc(&inode->i_dio_count);
 			down_read(&EXT4_I(inode)->i_data_sem);
 			mutex_unlock(&inode->i_mutex);
 		}
@@ -3134,6 +3135,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 		if (overwrite) {
 			up_read(&EXT4_I(inode)->i_data_sem);
 			mutex_lock(&inode->i_mutex);
+			inode_dio_done(inode);
 		}
 
 		return ret;
-- 
1.7.7.6