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.
Changes agains V1:
- wake up dio waiters before i_mutex.
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
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 a850026..c5c4f9d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3014,6 +3014,7 @@ 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);
}
@@ -3111,6 +3112,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
retake_lock:
/* take i_mutex locking again if we do a ovewrite dio */
if (overwrite) {
+ inode_dio_done(inode);
up_read(&EXT4_I(inode)->i_data_sem);
mutex_lock(&inode->i_mutex);
}
--
1.7.7.6
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