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    Subject[PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correctly
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    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);
    } else {
    aio_complete(iocb, ret, 0);
    inode_dio_done(inode);



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