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? > + 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; > } > [..]