Re: [RFC PATCH v3 net-next 6/7] net: ethtool: add a mutex protecting RSS contexts

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 8977aa8523e3..1f8293deebd5 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:		IDR storing custom RSS context state
+ * @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 idr		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 f12767466427..2acb4d8cd4c7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -10054,6 +10054,7 @@ int register_netdevice(struct net_device *dev)
 	idr_init_base(&dev->ethtool->rss_ctx, 1);
 
 	spin_lock_init(&dev->addr_list_lock);
+	mutex_init(&dev->ethtool->rss_lock);