Re: [PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correctly

Jan Kara
2012-11-20T10:16:04Z

On Mon 19-11-12 23:51:15, Darrick J. Wong wrote:
> When performing O_SYNC+AIO+DIO writes to block devices, use the DIO_SYNC_WRITES
> flag so that flushes are issued /after/ the write completes, not before.
>
> Note, however, that for block devices, the DIO setup code ensures that a flush
> wq is attached to the superblock of the bdevfs filesystem, not the filesystem
> that the device node happens to reside in. This means that unlike regular
> files, iocb->ki_filp->f_mapping->host->i_sb != inode->i_sb. Therefore, adjust
> Jeff's earlier patch to keep the pointer use consistent and avoid a NULL deref.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
> fs/block_dev.c | 5 +++--
> fs/direct-io.c | 3 ++-
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 1a1e5e3..05ff33a 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -235,7 +235,8 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
> struct inode *inode = file->f_mapping->host;
>
> return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
> - nr_segs, blkdev_get_blocks, NULL, NULL, 0);
> + nr_segs, blkdev_get_blocks, NULL, NULL,
> + DIO_SYNC_WRITES);
> }
>
> int __sync_blockdev(struct block_device *bdev, int wait)
> @@ -1631,7 +1632,7 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov,
> percpu_down_read(&bdev->bd_block_size_semaphore);
>
> ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
> - if (ret > 0 || ret == -EIOCBQUEUED) {
> + if (ret > 0) {
> ssize_t err;
>
> err = generic_write_sync(file, pos, ret);
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index b7391d4..c626c43 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -258,7 +258,8 @@ void generic_dio_end_io(struct kiocb *iocb, loff_t offset, ssize_t bytes,
> work->ret = ret;
> work->offset = offset;
> work->len = bytes;
> - queue_work(inode->i_sb->s_dio_flush_wq, &work->work);
> + queue_work(iocb->ki_filp->f_mapping->host->i_sb->s_dio_flush_wq,
> + &work->work);
This should be folded into the original patch introducing the
s_dio_flush_wq. And please add a comment before this line saying that block
devices need a dereference exactly like this... Otherwise the patch looks
good so you can add:
Reviewed-by: Jan Kara <jack@suse.cz>

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR