netdev - [PATCH net-next] net: no longer acquire RTNL in threaded

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Message-ID: <20240502173926.2010646-1-edumazet@google.com>
Date: Thu,  2 May 2024 17:39:26 +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: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] net: no longer acquire RTNL in threaded_show()

dev->threaded can be read locklessly, if we add
corresponding READ_ONCE()/WRITE_ONCE() annotations.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/netdevice.h | 2 +-
 net/core/dev.c            | 4 ++--
 net/core/net-sysfs.c      | 8 ++++----
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 41853424b41d7a95e896e2f62318c161468c2437..2814a15eed73bfe27be6dc490b2e030158f86ead 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2370,8 +2370,8 @@ struct net_device {
 	struct sfp_bus		*sfp_bus;
 	struct lock_class_key	*qdisc_tx_busylock;
 	bool			proto_down;
+	bool			threaded;
 	unsigned		wol_enabled:1;
-	unsigned		threaded:1;
 
 	struct list_head	net_notifier_list;
 
diff --git a/net/core/dev.c b/net/core/dev.c
index e02d2363347e2e403ccb2a59d44d35cee9a1b367..d6b24749eb2e27ca87609e31b0434c6c09f0e8d8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6531,7 +6531,7 @@ int dev_set_threaded(struct net_device *dev, bool threaded)
 		}
 	}
 
-	dev->threaded = threaded;
+	WRITE_ONCE(dev->threaded, threaded);
 
 	/* Make sure kthread is created before THREADED bit
 	 * is set.
@@ -6622,7 +6622,7 @@ void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
 	 * threaded mode will not be enabled in napi_enable().
 	 */
 	if (dev->threaded && napi_kthread_create(napi))
-		dev->threaded = 0;
+		dev->threaded = false;
 	netif_napi_set_irq(napi, -1);
 }
 EXPORT_SYMBOL(netif_napi_add_weight);
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 1f7f09e567715f418bc163079d0dd19c51c3571c..4c27a360c2948e520b6cf06934553d82e250057d 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -605,13 +605,13 @@ static ssize_t threaded_show(struct device *dev,
 	struct net_device *netdev = to_net_dev(dev);
 	ssize_t ret = -EINVAL;
 
-	if (!rtnl_trylock())
-		return restart_syscall();
+	rcu_read_lock();
 
 	if (dev_isalive(netdev))
-		ret = sysfs_emit(buf, fmt_dec, netdev->threaded);
+		ret = sysfs_emit(buf, fmt_dec, READ_ONCE(netdev->threaded));
+
+	rcu_read_unlock();
 
-	rtnl_unlock();
 	return ret;
 }
 
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog