net: ethtool: move rxfh_fields callbacks under the rss_lock

Netlink code will want to perform the RSS_SET operation atomically
under the rss_lock. sfc wants to hold the rss_lock in rxfh_fields_get,
which makes that difficult. Lets move the locking up to the core
so that for all driver-facing callbacks rss_lock is taken consistently
by the core.

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/sfc/ethtool_common.c

···
 
 	ctx = &efx->rss_context.priv;
 
-	mutex_lock(&net_dev->ethtool->rss_lock);
 	if (info->rss_context) {
 		ctx = efx_find_rss_context_entry(efx, info->rss_context);
-		if (!ctx) {
-			rc = -ENOENT;
-			goto out_unlock;
-		}
+		if (!ctx)
+			return -ENOENT;
 	}
 
 	data = 0;
···
 	}
 out_setdata_unlock:
 	info->data = data;
-out_unlock:
-	mutex_unlock(&net_dev->ethtool->rss_lock);
 	return rc;
 }
 

net/ethtool/ioctl.c

···
 	if (info.flow_type & FLOW_RSS)
 		fields.rss_context = info.rss_context;
 
-	return ops->set_rxfh_fields(dev, &fields, NULL);
+	mutex_lock(&dev->ethtool->rss_lock);
+	rc = ops->set_rxfh_fields(dev, &fields, NULL);
+	mutex_unlock(&dev->ethtool->rss_lock);
+	return rc;
 }
 
 static noinline_for_stack int
···
 	if (info.flow_type & FLOW_RSS)
 		fields.rss_context = info.rss_context;
 
+	mutex_lock(&dev->ethtool->rss_lock);
 	ret = ops->get_rxfh_fields(dev, &fields);
+	mutex_unlock(&dev->ethtool->rss_lock);
 	if (ret < 0)
 		return ret;
 
···
 	     rxfh.input_xfrm == RXH_XFRM_NO_CHANGE))
 		return -EINVAL;
 
-	ret = ethtool_check_flow_types(dev, rxfh.input_xfrm);
-	if (ret)
-		return ret;
-
 	indir_bytes = dev_indir_size * sizeof(rxfh_dev.indir[0]);
 
 	/* Check settings which may be global rather than per RSS-context */
···
 	}
 
 	mutex_lock(&dev->ethtool->rss_lock);
+
+	ret = ethtool_check_flow_types(dev, rxfh.input_xfrm);
+	if (ret)
+		goto out_unlock;
 
 	if (rxfh.rss_context && rxfh_dev.rss_delete) {
 		ret = ethtool_check_rss_ctx_busy(dev, rxfh.rss_context);