virtio-pci: check name when counting MSI-X vectors

to #26589565

commit 5790b53390e18fdd21e70776e46d058c05eda2f2 upstream

VQs without a name specified are not valid; they are skipped in the
later loop that assigns MSI-X vectors to queues, but the per_vq_vectors
loop above that counts the required number of vectors previously still
counted any queue with a non-NULL callback as needing a vector.

Add a check to the per_vq_vectors loop so that vectors with no name are
not counted to make the two loops consistent.  This prevents
over-counting unnecessary vectors (e.g. for features which were not
negotiated with the device).

Cc: stable@vger.kernel.org
Fixes: 86a559787e6f ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
Reviewed-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NDaniel Verkamp <dverkamp@chromium.org>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NWang, Wei W <wei.w.wang@intel.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: NShile Zhang <shile.zhang@linux.alibaba.com>

drivers/virtio/virtio_pci_common.c

@@ -297,7 +297,7 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
 		/* Best option: one for change interrupt, one per vq. */
 		nvectors = 1;
 		for (i = 0; i < nvqs; ++i)
-			if (callbacks[i])
+			if (names[i] && callbacks[i])
 				++nvectors;
 	} else {
 		/* Second best: one for change, shared for all vqs. */