[PATCH v4 net-next 6/7] net: ethtool: add a mutex protecting RSS contexts

[<edward.cree@amd.com>]

From: Edward Cree <ecree.xilinx@gmail.com>

While this is not needed to serialise the ethtool entry points (which
 are all under RTNL), drivers may have cause to asynchronously access
 dev->ethtool->rss_ctx; taking dev->ethtool->rss_lock allows them to
 do this safely without needing to take the RTNL.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
---
 include/linux/ethtool.h | 3 +++
 net/core/dev.c          | 5 +++++
 net/ethtool/ioctl.c     | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index c8963bde9289..d15a21bd6f12 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -1026,11 +1026,14 @@ int ethtool_virtdev_set_link_ksettings(struct net_device *dev,
 /**
  * struct ethtool_netdev_state - per-netdevice state for ethtool features
  * @rss_ctx:		XArray of custom RSS contexts
+ * @rss_lock:		Protects entries in @rss_ctx.  May be taken from
+ *			within RTNL.
  * @rss_ctx_max_id:	maximum (exclusive) supported RSS context ID
  * @wol_enabled:	Wake-on-LAN is enabled
  */
 struct ethtool_netdev_state {
 	struct xarray		rss_ctx;
+	struct mutex		rss_lock;
 	u32			rss_ctx_max_id;
 	u32			wol_enabled:1;
 };
diff --git a/net/core/dev.c b/net/core/dev.c
index 69579d9cd7ba..c57456ed4be8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10074,6 +10074,7 @@ int register_netdevice(struct net_device *dev)
 
 	/* rss ctx ID 0 is reserved for the default context, start from 1 */
 	xa_init_flags(&dev->ethtool->rss_ctx, XA_FLAGS_ALLOC1);
+	mutex_init(&dev->ethtool->rss_lock);
 
 	spin_lock_init(&dev->addr_list_lock);
 	netdev_set_addr_lockdep_class(dev);
@@ -10882,6 +10883,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 	struct ethtool_rxfh_context *ctx;
 	unsigned long context;
 
+	mutex_lock(&dev->ethtool->rss_lock);
 	if (dev->ethtool_ops->create_rxfh_context ||
 	    dev->ethtool_ops->set_rxfh_context)
 		xa_for_each(&dev->ethtool->rss_ctx, context, ctx) {
@@ -10903,6 +10905,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 			kfree(ctx);
 		}
 	xa_destroy(&dev->ethtool->rss_ctx);
+	mutex_unlock(&dev->ethtool->rss_lock);
 }
 
 /**
@@ -11016,6 +11019,8 @@ void unregister_netdevice_many_notify(struct list_head *head,
 		if (dev->netdev_ops->ndo_uninit)
 			dev->netdev_ops->ndo_uninit(dev);
 
+		mutex_destroy(&dev->ethtool->rss_lock);
+
 		if (skb)
 			rtmsg_ifinfo_send(skb, dev, GFP_KERNEL, portid, nlh);
 
diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 3920ddee3ee2..d21bbc92e6fc 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1258,6 +1258,7 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 	u8 *rss_config;
 	u32 rss_cfg_offset = offsetof(struct ethtool_rxfh, rss_config[0]);
 	bool create = false, delete = false;
+	bool locked = false; /* dev->ethtool->rss_lock taken */
 
 	if (!ops->get_rxnfc || !ops->set_rxfh)
 		return -EOPNOTSUPP;
@@ -1335,6 +1336,10 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 		}
 	}
 
+	if (rxfh.rss_context) {
+		mutex_lock(&dev->ethtool->rss_lock);
+		locked = true;
+	}
 	if (create) {
 		if (delete) {
 			ret = -EINVAL;
@@ -1455,6 +1460,8 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 	}
 
 out:
+	if (locked)
+		mutex_unlock(&dev->ethtool->rss_lock);
 	kfree(rss_config);
 	return ret;
 }