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

Jeff Moyer
2012-11-20T20:48:10Z

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?

Cheers,
Jeff