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

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Date: Tue, 12 Sep 2023 15:21:41 +0100
From: <edward.cree@....com>
To: <linux-net-drivers@....com>, <davem@...emloft.net>, <kuba@...nel.org>,
	<edumazet@...gle.com>, <pabeni@...hat.com>
CC: Edward Cree <ecree.xilinx@...il.com>, <netdev@...r.kernel.org>,
	<habetsm.xilinx@...il.com>, <sudheer.mogilappagari@...el.com>,
	<jdamato@...tly.com>, <andrew@...n.ch>, <mw@...ihalf.com>,
	<linux@...linux.org.uk>, <sgoutham@...vell.com>, <gakula@...vell.com>,
	<sbhatta@...vell.com>, <hkelam@...vell.com>, <saeedm@...dia.com>,
	<leon@...nel.org>
Subject: [RFC PATCH v3 net-next 6/7] net: ethtool: add a mutex protecting RSS contexts

From: Edward Cree <ecree.xilinx@...il.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@...il.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);
 	netdev_set_addr_lockdep_class(dev);
 
 	ret = dev_get_valid_name(net, dev, dev->name);
@@ -10863,6 +10864,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 	if (!dev->ethtool_ops->create_rxfh_context &&
 	    !dev->ethtool_ops->set_rxfh_context)
 		return;
+	mutex_lock(&dev->ethtool->rss_lock);
 	idr_for_each_entry(&dev->ethtool->rss_ctx, ctx, context) {
 		u32 *indir = ethtool_rxfh_context_indir(ctx);
 		u8 *key = ethtool_rxfh_context_key(ctx);
@@ -10877,6 +10879,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 							   &context, true);
 		kfree(ctx);
 	}
+	mutex_unlock(&dev->ethtool->rss_lock);
 }
 
 /**
@@ -10990,6 +10993,8 @@ 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 5b943db75974..70cca80cea70 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;
@@ -1457,6 +1462,8 @@ 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;
 }