Commit 2628f495 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

net: add helpers for lookup and walking netdevs under netdev_lock() 



Add helpers for accessing netdevs under netdev_lock().
There's some careful handling needed to find the device and lock it
safely, without it getting unregistered, and without taking rtnl_lock
(the latter being the whole point of the new locking, after all).

Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115035319.559603-4-kuba@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 5fda3f35

net/core/dev.c

+110 −0
Original line number Diff line number Diff line
@@ -784,6 +784,49 @@ struct napi_struct *netdev_napi_by_id(struct net *net, unsigned int napi_id) 
	return napi;

}



/**

 *	netdev_napi_by_id_lock() - find a device by NAPI ID and lock it

 *	@net: the applicable net namespace

 *	@napi_id: ID of a NAPI of a target device

 *

 *	Find a NAPI instance with @napi_id. Lock its device.

 *	The device must be in %NETREG_REGISTERED state for lookup to succeed.

 *	netdev_unlock() must be called to release it.

 *

 *	Return: pointer to NAPI, its device with lock held, NULL if not found.

 */

struct napi_struct *

netdev_napi_by_id_lock(struct net *net, unsigned int napi_id)

{

	struct napi_struct *napi;

	struct net_device *dev;



	rcu_read_lock();

	napi = netdev_napi_by_id(net, napi_id);

	if (!napi || READ_ONCE(napi->dev->reg_state) != NETREG_REGISTERED) {

		rcu_read_unlock();

		return NULL;

	}



	dev = napi->dev;

	dev_hold(dev);

	rcu_read_unlock();



	dev = __netdev_put_lock(dev);

	if (!dev)

		return NULL;



	rcu_read_lock();

	napi = netdev_napi_by_id(net, napi_id);

	if (napi && napi->dev != dev)

		napi = NULL;

	rcu_read_unlock();



	if (!napi)

		netdev_unlock(dev);

	return napi;

}



/**

 *	__dev_get_by_name	- find a device by its name

 *	@net: the applicable net namespace
@@ -972,6 +1015,73 @@ struct net_device *dev_get_by_napi_id(unsigned int napi_id) 
	return napi ? napi->dev : NULL;

}



/* Release the held reference on the net_device, and if the net_device

 * is still registered try to lock the instance lock. If device is being

 * unregistered NULL will be returned (but the reference has been released,

 * either way!)

 *

 * This helper is intended for locking net_device after it has been looked up

 * using a lockless lookup helper. Lock prevents the instance from going away.

 */

struct net_device *__netdev_put_lock(struct net_device *dev)

{

	netdev_lock(dev);

	if (dev->reg_state > NETREG_REGISTERED) {

		netdev_unlock(dev);

		dev_put(dev);

		return NULL;

	}

	dev_put(dev);

	return dev;

}



/**

 *	netdev_get_by_index_lock() - find a device by its ifindex

 *	@net: the applicable net namespace

 *	@ifindex: index of device

 *

 *	Search for an interface by index. If a valid device

 *	with @ifindex is found it will be returned with netdev->lock held.

 *	netdev_unlock() must be called to release it.

 *

 *	Return: pointer to a device with lock held, NULL if not found.

 */

struct net_device *netdev_get_by_index_lock(struct net *net, int ifindex)

{

	struct net_device *dev;



	dev = dev_get_by_index(net, ifindex);

	if (!dev)

		return NULL;



	return __netdev_put_lock(dev);

}



struct net_device *

netdev_xa_find_lock(struct net *net, struct net_device *dev,

		    unsigned long *index)

{

	if (dev)

		netdev_unlock(dev);



	do {

		rcu_read_lock();

		dev = xa_find(&net->dev_by_index, index, ULONG_MAX, XA_PRESENT);

		if (!dev) {

			rcu_read_unlock();

			return NULL;

		}

		dev_hold(dev);

		rcu_read_unlock();



		dev = __netdev_put_lock(dev);

		if (dev)

			return dev;



		(*index)++;

	} while (true);

}



static DEFINE_SEQLOCK(netdev_rename_lock);



void netdev_copy_name(struct net_device *dev, char *name)

net/core/dev.h

+16 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#ifndef _NET_CORE_DEV_H

#define _NET_CORE_DEV_H



#include <linux/cleanup.h>

#include <linux/types.h>

#include <linux/rwsem.h>

#include <linux/netdevice.h>
@@ -23,8 +24,23 @@ struct sd_flow_limit { 
extern int netdev_flow_limit_table_len;



struct napi_struct *netdev_napi_by_id(struct net *net, unsigned int napi_id);

struct napi_struct *

netdev_napi_by_id_lock(struct net *net, unsigned int napi_id);

struct net_device *dev_get_by_napi_id(unsigned int napi_id);



struct net_device *netdev_get_by_index_lock(struct net *net, int ifindex);

struct net_device *__netdev_put_lock(struct net_device *dev);

struct net_device *

netdev_xa_find_lock(struct net *net, struct net_device *dev,

		    unsigned long *index);



DEFINE_FREE(netdev_unlock, struct net_device *, if (_T) netdev_unlock(_T));



#define for_each_netdev_lock_scoped(net, var_name, ifindex)		\

	for (struct net_device *var_name __free(netdev_unlock) = NULL;	\

	     (var_name = netdev_xa_find_lock(net, var_name, &ifindex)); \

	     ifindex++)



#ifdef CONFIG_PROC_FS

int __init dev_proc_init(void);

#else