xen-blkfront: move negotiate_mq to cover all cases of new VBDs

negotiate_mq should happen in all cases of a new VBD being discovered by
xen-blkfront, whether called through _probe() or a hot-attached new VBD
from dom-0 via xenstore. Otherwise, hot-attached new VBDs are left
configured without multi-queue.

Signed-off-by: Bhavesh Davda <bhavesh.davda@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Author: Bhavesh Davda

drivers/block/xen-blkfront.c

@@ -262,6 +262,7 @@ static DEFINE_SPINLOCK(minor_lock);
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo);
 static void blkfront_gather_backend_features(struct blkfront_info *info);
+static int negotiate_mq(struct blkfront_info *info);
 
 static int get_id_from_freelist(struct blkfront_ring_info *rinfo)
 {
@@ -1774,11 +1775,18 @@ static int talk_to_blkback(struct xenbus_device *dev,
 	unsigned int i, max_page_order;
 	unsigned int ring_page_order;
 
+	if (!info)
+		return -ENODEV;
+
 	max_page_order = xenbus_read_unsigned(info->xbdev->otherend,
 					      "max-ring-page-order", 0);
 	ring_page_order = min(xen_blkif_max_ring_order, max_page_order);
 	info->nr_ring_pages = 1 << ring_page_order;
 
+	err = negotiate_mq(info);
+	if (err)
+		goto destroy_blkring;
+
 	for (i = 0; i < info->nr_rings; i++) {
 		struct blkfront_ring_info *rinfo = &info->rinfo[i];
 
@@ -1978,11 +1986,6 @@ static int blkfront_probe(struct xenbus_device *dev,
 	}
 
 	info->xbdev = dev;
-	err = negotiate_mq(info);
-	if (err) {
-		kfree(info);
-		return err;
-	}
 
 	mutex_init(&info->mutex);
 	info->vdevice = vdevice;
@@ -2099,10 +2102,6 @@ static int blkfront_resume(struct xenbus_device *dev)
 
 	blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
 
-	err = negotiate_mq(info);
-	if (err)
-		return err;
-
 	err = talk_to_blkback(dev, info);
 	if (!err)
 		blk_mq_update_nr_hw_queues(&info->tag_set, info->nr_rings);