On Mon, 21 Jan 2019 21:20:18 +0100
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
> On Mon, 21 Jan 2019 12:03:51 +0100
> Cornelia Huck <cohuck@xxxxxxxxxx> wrote:
>
> > Rework handling of multiple I/O requests to return -EAGAIN if
> > we are already processing an I/O request. Introduce a mutex
> > to disallow concurrent writes to the I/O region.
> >
> > The expectation is that userspace simply retries the operation
> > if it gets -EAGAIN.
> >
> > We currently don't allow multiple ssch requests at the same
> > time, as we don't have support for keeping channel programs
> > around for more than one request.
> >
> > Signed-off-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> > ---
>
> [..]
>
> > static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
> > @@ -188,25 +192,30 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
> > {
> > struct vfio_ccw_private *private;
> > struct ccw_io_region *region;
> > + int ret;
> >
> > if (*ppos + count > sizeof(*region))
> > return -EINVAL;
> >
> > private = dev_get_drvdata(mdev_parent_dev(mdev));
> > - if (private->state != VFIO_CCW_STATE_IDLE)
> > + if (private->state == VFIO_CCW_STATE_NOT_OPER ||
> > + private->state == VFIO_CCW_STATE_STANDBY)
> > return -EACCES;
> > + if (!mutex_trylock(&private->io_mutex))
> > + return -EAGAIN;
> >
> > region = private->io_region;
> > - if (copy_from_user((void *)region + *ppos, buf, count))
> > - return -EFAULT;
> > + if (copy_from_user((void *)region + *ppos, buf, count)) {
>
> This might race with vfio_ccw_sch_io_todo() on
> private->io_region->irb_area, or?
Ah yes, this should also take the mutex (should work because we're on a
workqueue).
>
> > + ret = -EFAULT;
> > + goto out_unlock;
> > + }
> >
> > vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_IO_REQ);
> > - if (region->ret_code != 0) {
> > - private->state = VFIO_CCW_STATE_IDLE;
> > - return region->ret_code;
> > - }
> > + ret = (region->ret_code != 0) ? region->ret_code : count;
> >
> > - return count;
> > +out_unlock:
> > + mutex_unlock(&private->io_mutex);
> > + return ret;
> > }
> >
> [..]
>
