Commit 5112457f authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

net: add netdev->up protected by netdev_lock() 



Some uAPI (netdev netlink) hide net_device's sub-objects while
the interface is down to ensure uniform behavior across drivers.
To remove the rtnl_lock dependency from those uAPIs we need a way
to safely tell if the device is down or up.

Add an indication of whether device is open or closed, protected
by netdev->lock. The semantics are the same as IFF_UP, but taking
netdev_lock around every write to ->flags would be a lot of code
churn.

We don't want to blanket the entire open / close path by netdev_lock,
because it will prevent us from applying it to specific structures -
core helpers won't be able to take that lock from any function
called by the drivers on open/close paths.

So the state of the flag is "pessimistic", as in it may report false
negatives, but never false positives.

Reviewed-by: default avatarJoe Damato <jdamato@fastly.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115035319.559603-5-kuba@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 2628f495

include/linux/netdevice.h

+13 −1
Original line number Diff line number Diff line
@@ -2443,12 +2443,24 @@ struct net_device { 
	unsigned long		gro_flush_timeout;

	u32			napi_defer_hard_irqs;



	/**

	 * @up: copy of @state's IFF_UP, but safe to read with just @lock.

	 *	May report false negatives while the device is being opened

	 *	or closed (@lock does not protect .ndo_open, or .ndo_close).

	 */

	bool			up;



	/**

	 * @lock: netdev-scope lock, protects a small selection of fields.

	 * Should always be taken using netdev_lock() / netdev_unlock() helpers.

	 * Drivers are free to use it for other protection.

	 *

	 * Protects: @reg_state, @net_shaper_hierarchy.

	 * Protects:

	 *	@net_shaper_hierarchy, @reg_state

	 *

	 * Partially protects (writers must hold both @lock and rtnl_lock):

	 *	@up

	 *

	 * Ordering: take after rtnl_lock.

	 */

	struct mutex		lock;

net/core/dev.c

+2 −2
Original line number Diff line number Diff line
@@ -1619,7 +1619,7 @@ static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack) 
	if (ret)

		clear_bit(__LINK_STATE_START, &dev->state);

	else {

		dev->flags |= IFF_UP;

		netif_set_up(dev, true);

		dev_set_rx_mode(dev);

		dev_activate(dev);

		add_device_randomness(dev->dev_addr, dev->addr_len);
@@ -1698,7 +1698,7 @@ static void __dev_close_many(struct list_head *head) 
		if (ops->ndo_stop)

			ops->ndo_stop(dev);



		dev->flags &= ~IFF_UP;

		netif_set_up(dev, false);

		netpoll_poll_enable(dev);

	}

}

net/core/dev.h

+12 −0
Original line number Diff line number Diff line
@@ -128,6 +128,18 @@ void __dev_notify_flags(struct net_device *dev, unsigned int old_flags, 
void unregister_netdevice_many_notify(struct list_head *head,

				      u32 portid, const struct nlmsghdr *nlh);



static inline void netif_set_up(struct net_device *dev, bool value)

{

	if (value)

		dev->flags |= IFF_UP;

	else

		dev->flags &= ~IFF_UP;



	netdev_lock(dev);

	dev->up = value;

	netdev_unlock(dev);

}



static inline void netif_set_gso_max_size(struct net_device *dev,

					  unsigned int size)

{