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

Jan Kara
2012-11-21T00:57:42Z

On Tue 20-11-12 15:47:54, Jeff Moyer wrote:
> Jan Kara <jack@suse.cz> writes:
>
> > 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>
>
> When you say, "This," do you mean that one change, or the whole patch?
I meant the whole patch after that hung is folded ;)

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