On Thu, 22 Oct 2020 13:12:04 -0400
Tony Krowiak <akrow...@linux.ibm.com> wrote:
> +static int vfio_ap_mdev_validate_masks(struct ap_matrix_mdev *matrix_mdev,
> + unsigned long *mdev_apm,
> + unsigned long *mdev_aqm)
> +{
> + if (ap_apqn_in_matrix_owned_by_def_drv(mdev_apm, mdev_aqm))
> + return -EADDRNOTAVAIL;
> +
> + return vfio_ap_mdev_verify_no_sharing(matrix_mdev, mdev_apm, mdev_aqm);
> +}
> +
> static bool vfio_ap_mdev_matrixes_equal(struct ap_matrix *matrix1,
> struct ap_matrix *matrix2)
> {
> @@ -840,33 +734,21 @@ static ssize_t assign_adapter_store(struct device *dev,
> if (apid > matrix_mdev->matrix.apm_max)
> return -ENODEV;
>
> - /*
> - * Set the bit in the AP mask (APM) corresponding to the AP adapter
> - * number (APID). The bits in the mask, from most significant to least
> - * significant bit, correspond to APIDs 0-255.
> - */
> - mutex_lock(&matrix_dev->lock);
> -
> - ret = vfio_ap_mdev_verify_queues_reserved_for_apid(matrix_mdev, apid);
> - if (ret)
> - goto done;
> -
> memset(apm, 0, sizeof(apm));
> set_bit_inv(apid, apm);
>
> - ret = vfio_ap_mdev_verify_no_sharing(matrix_mdev, apm,
> - matrix_mdev->matrix.aqm);
> - if (ret)
> - goto done;
> -
> + mutex_lock(&matrix_dev->lock);
> + ret = vfio_ap_mdev_validate_masks(matrix_mdev, apm,
> + matrix_mdev->matrix.aqm);
Is this a potential deadlock?
Consider following scenario
1) apmask_store() takes ap_perms_mutex
2) assign_adapter_store() takes matrix_dev->lock
3) apmask_store() calls vfio_ap_mdev_resource_in_use() which tries
to take matrix_dev->lock
4) assign_adapter_store() calls ap_apqn_in_matrix_owned_by_def_drv
which tries to take ap_perms_mutex
BANG!
I think using mutex_trylock(&matrix_dev->lock) and bailing out with busy
if we don't manage to acquire the lock would be a good idea anyway, to
prevent a bunch of mdev management operations piling up on the mutex
and starving in_use().
Regards,
Halil
> + if (ret) {
> + mutex_unlock(&matrix_dev->lock);
> + return ret;
> + }
> set_bit_inv(apid, matrix_mdev->matrix.apm);
> vfio_ap_mdev_link_queues(matrix_mdev, LINK_APID, apid);
> - ret = count;
> -
> -done:
> mutex_unlock(&matrix_dev->lock);
>
> - return ret;
> + return count;
