netdev - [PATCH net-next 1/6] net: ethtool: grab a netdev reference in dev

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Message-ID: <20240620114711.777046-2-edumazet@google.com>
Date: Thu, 20 Jun 2024 11:47:06 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Ziwei Xiao <ziweixiao@...gle.com>, Praveen Kaligineedi <pkaligineedi@...gle.com>, 
	Harshitha Ramamurthy <hramamurthy@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Jeroen de Borst <jeroendb@...gle.com>, Shailend Chand <shailend@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/6] net: ethtool: grab a netdev reference in dev_ethtool()

We would like to not always grab RTNL for some commands in the future,
to decrease RTNL pressure.

Grab a reference on the device to ensure it will not disappear while
dev_ethtool() is running.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ethtool/ioctl.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index e645d751a5e8998064ef5fa239d465f66c044e6f..01c52159aef7a47165ef11aab2c599ffe4ad345d 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -2851,18 +2851,14 @@ static int ethtool_set_fecparam(struct net_device *dev, void __user *useraddr)
 /* The main entry point in this file.  Called from net/core/dev_ioctl.c */
 
 static int
-__dev_ethtool(struct net *net, struct ifreq *ifr, void __user *useraddr,
-	      u32 ethcmd, struct ethtool_devlink_compat *devlink_state)
+__dev_ethtool(struct net *net, struct net_device *dev, struct ifreq *ifr,
+	      void __user *useraddr, u32 ethcmd,
+	      struct ethtool_devlink_compat *devlink_state)
 {
-	struct net_device *dev;
 	u32 sub_cmd;
 	int rc;
 	netdev_features_t old_features;
 
-	dev = __dev_get_by_name(net, ifr->ifr_name);
-	if (!dev)
-		return -ENODEV;
-
 	if (ethcmd == ETHTOOL_PERQUEUE) {
 		if (copy_from_user(&sub_cmd, useraddr + sizeof(ethcmd), sizeof(sub_cmd)))
 			return -EFAULT;
@@ -3153,6 +3149,8 @@ __dev_ethtool(struct net *net, struct ifreq *ifr, void __user *useraddr,
 int dev_ethtool(struct net *net, struct ifreq *ifr, void __user *useraddr)
 {
 	struct ethtool_devlink_compat *state;
+	netdevice_tracker dev_tracker;
+	struct net_device *dev;
 	u32 ethcmd;
 	int rc;
 
@@ -3173,9 +3171,16 @@ int dev_ethtool(struct net *net, struct ifreq *ifr, void __user *useraddr)
 		break;
 	}
 
+	rc = -ENODEV;
+	dev = netdev_get_by_name(net, ifr->ifr_name, &dev_tracker, GFP_KERNEL);
+	if (!dev)
+		goto exit_free;
+
 	rtnl_lock();
-	rc = __dev_ethtool(net, ifr, useraddr, ethcmd, state);
+	rc = __dev_ethtool(net, dev, ifr, useraddr, ethcmd, state);
 	rtnl_unlock();
+	netdev_put(dev, &dev_tracker);
+
 	if (rc)
 		goto exit_free;
 
-- 
2.45.2.627.g7a2c4fd464-goog