Re: [PATCH 06/19] io_uring: add fsync support

[Jann Horn <jannh@google.com>]

On Fri, Feb 8, 2019 at 6:34 PM Jens Axboe <axboe@kernel.dk> wrote:
> From: Christoph Hellwig <hch@lst.de>
>
> Add a new fsync opcode, which either syncs a range if one is passed,
> or the whole file if the offset and length fields are both cleared
> to zero.  A flag is provided to use fdatasync semantics, that is only
> force out metadata which is required to retrieve the file data, but
> not others like metadata.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
[...]
> +static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
> +                   bool force_nonblock)
> +{
> +       struct io_ring_ctx *ctx = req->ctx;
> +       loff_t sqe_off = READ_ONCE(sqe->off);
> +       loff_t sqe_len = READ_ONCE(sqe->len);
> +       loff_t end = sqe_off + sqe_len;
> +       unsigned fsync_flags;
> +       struct file *file;
> +       int ret, fd;
> +
> +       /* fsync always requires a blocking context */
> +       if (force_nonblock)
> +               return -EAGAIN;
> +
> +       if (unlikely(sqe->addr || sqe->ioprio))
> +               return -EINVAL;
> +
> +       fsync_flags = READ_ONCE(sqe->fsync_flags);
> +       if (unlikely(fsync_flags & ~IORING_FSYNC_DATASYNC))
> +               return -EINVAL;
> +
> +       fd = READ_ONCE(sqe->fd);
> +       file = fget(fd);

This always runs on the workqueue, right? Is it possible to call
fget() on a workqueue?

> +       if (unlikely(!file))
> +               return -EBADF;
> +
> +       ret = vfs_fsync_range(file, sqe_off, end > 0 ? end : LLONG_MAX,
> +                               fsync_flags & IORING_FSYNC_DATASYNC);
> +
> +       fput(file);
> +       io_cqring_add_event(ctx, sqe->user_data, ret, 0);
> +       io_free_req(req);
> +       return 0;
> +}