On Mon 12-03-18 23:21:55, Eryu Guan wrote:
> i_disksize update should be protected by i_data_sem, by either taking
> the lock explicitly or by using ext4_update_i_disksize() helper. But the
> i_disksize updates in ext4_direct_IO_write() are not protected at all,
> which may be racing with i_disksize updates in writeback path in
> delalloc buffer write path.
>
> This is found by code inspection, and I didn't hit any i_disksize
> corruption due to this bug. Thanks to Jan Kara for catching this bug and
> suggesting the fix!
>
> Reported-by: Jan Kara <jack@xxxxxxx>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
Looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
>
> There's no v1 version of this patch.
>
> It's a bit unfortunate that I have to remove the "ei" definition in this
> patch and reintroduce it in patch 2/2, otherwise I got transient
> "defined but not used" build warning with only this patch applied.
>
> fs/ext4/inode.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index c94780075b04..bff44b4a0783 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3658,7 +3658,6 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
> {
> struct file *file = iocb->ki_filp;
> struct inode *inode = file->f_mapping->host;
> - struct ext4_inode_info *ei = EXT4_I(inode);
> ssize_t ret;
> loff_t offset = iocb->ki_pos;
> size_t count = iov_iter_count(iter);
> @@ -3682,7 +3681,7 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
> goto out;
> }
> orphan = 1;
> - ei->i_disksize = inode->i_size;
> + ext4_update_i_disksize(inode, inode->i_size);
> ext4_journal_stop(handle);
> }
>
> @@ -3790,7 +3789,7 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
> if (ret > 0) {
> loff_t end = offset + ret;
> if (end > inode->i_size) {
> - ei->i_disksize = end;
> + ext4_update_i_disksize(inode, end);
> i_size_write(inode, end);
> /*
> * We're going to return a positive `ret'
> --
> 2.14.3
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
