netdev - [RFC PATCH net-next 5/6] net: ethtool: add a mutex protecting RSS contexts

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Date:   Mon, 3 Apr 2023 17:33:02 +0100
From:   <edward.cree@....com>
To:     <linux-net-drivers@....com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>
CC:     Edward Cree <ecree.xilinx@...il.com>, <netdev@...r.kernel.org>,
        <habetsm.xilinx@...il.com>, <sudheer.mogilappagari@...el.com>
Subject: [RFC PATCH net-next 5/6] 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->rss_ctx; taking dev->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/netdevice.h | 3 +++
 net/core/dev.c            | 5 +++++
 net/ethtool/ioctl.c       | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 91f7dad070bd..598bbffdcfd2 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2030,6 +2030,8 @@ enum netdev_ml_priv_type {
  *	@udp_tunnel_nic:	UDP tunnel offload state
  *	@rss_ctx_max_id:	maximum (exclusive) supported RSS context ID
  *	@rss_ctx:	IDR storing custom RSS context state
+ *	@rss_lock:	Protects entries in @rss_ctx.  May be taken from
+ *			within RTNL.
  *	@xdp_state:		stores info on attached XDP BPF programs
  *
  *	@nested_level:	Used as a parameter of spin_lock_nested() of
@@ -2401,6 +2403,7 @@ struct net_device {
 
 	u32			rss_ctx_max_id;
 	struct idr		rss_ctx;
+	struct mutex		rss_lock;
 
 	/* protected by rtnl_lock */
 	struct bpf_xdp_entity	xdp_state[__MAX_XDP_MODE];
diff --git a/net/core/dev.c b/net/core/dev.c
index b2cfc631761d..8309178e9d1a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9987,6 +9987,7 @@ int register_netdevice(struct net_device *dev)
 	idr_init_base(&dev->rss_ctx, 1);
 
 	spin_lock_init(&dev->addr_list_lock);
+	mutex_init(&dev->rss_lock);
 	netdev_set_addr_lockdep_class(dev);
 
 	ret = dev_get_valid_name(net, dev, dev->name);
@@ -10788,6 +10789,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 	if (!dev->ethtool_ops->set_rxfh_context &&
 	    !dev->ethtool_ops->set_rxfh_context_old)
 		return;
+	mutex_lock(&dev->rss_lock);
 	idr_for_each_entry(&dev->rss_ctx, ctx, context) {
 		u32 *indir = ethtool_rxfh_context_indir(ctx);
 		u8 *key = ethtool_rxfh_context_key(ctx);
@@ -10804,6 +10806,7 @@ static void netdev_rss_contexts_free(struct net_device *dev)
 							       &context, true);
 		kfree(ctx);
 	}
+	mutex_unlock(&dev->rss_lock);
 }
 
 /**
@@ -10917,6 +10920,8 @@ void unregister_netdevice_many_notify(struct list_head *head,
 		if (dev->netdev_ops->ndo_uninit)
 			dev->netdev_ops->ndo_uninit(dev);
 
+		mutex_destroy(&dev->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 fa0a3de1e9fb..3d1190e3abb3 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1257,6 +1257,7 @@ 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->rss_lock taken */
 
 	if (!ops->get_rxnfc || !ops->set_rxfh)
 		return -EOPNOTSUPP;
@@ -1336,6 +1337,10 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 		}
 	}
 
+	if (rxfh.rss_context) {
+		mutex_lock(&dev->rss_lock);
+		locked = true;
+	}
 	if (create) {
 		if (delete) {
 			ret = -EINVAL;
@@ -1438,6 +1443,8 @@ static noinline_for_stack int ethtool_set_rxfh(struct net_device *dev,
 	}
 
 out:
+	if (locked)
+		mutex_unlock(&dev->rss_lock);
 	kfree(rss_config);
 	return ret;
 }