Commit 6c04bb18 authored by Johannes Berg's avatar Johannes Berg Committed by David S. Miller
Browse files

netlink: use call_rcu for netlink_change_ngroups 



For the network namespace work in generic netlink I need
to be able to call this function under rcu_read_lock(),
otherwise the locking becomes a nightmare and more locks
would be needed. Instead, just embed a struct rcu_head
(actually a struct listeners_rcu_head that also carries
the pointer to the memory block) into the listeners
memory so we can use call_rcu() instead of synchronising
and then freeing. No rcu_barrier() is needed since this
code cannot be modular.

Signed-off-by: default avatarJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 487420df

net/netlink/af_netlink.c

+30 −4
Original line number Original line Diff line number Diff line
@@ -83,6 +83,11 @@ struct netlink_sock { 
	struct module		*module;

	struct module		*module;

};

};





struct listeners_rcu_head {

	struct rcu_head rcu_head;

	void *ptr;

};



#define NETLINK_KERNEL_SOCKET	0x1

#define NETLINK_KERNEL_SOCKET	0x1

#define NETLINK_RECV_PKTINFO	0x2

#define NETLINK_RECV_PKTINFO	0x2

#define NETLINK_BROADCAST_SEND_ERROR	0x4

#define NETLINK_BROADCAST_SEND_ERROR	0x4
@@ -1453,7 +1458,8 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups, 
	if (groups < 32)

	if (groups < 32)

		groups = 32;

		groups = 32;





	listeners = kzalloc(NLGRPSZ(groups), GFP_KERNEL);

	listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head),

			    GFP_KERNEL);

	if (!listeners)

	if (!listeners)

		goto out_sock_release;

		goto out_sock_release;
@@ -1501,6 +1507,14 @@ netlink_kernel_release(struct sock *sk) 
EXPORT_SYMBOL(netlink_kernel_release);

EXPORT_SYMBOL(netlink_kernel_release);









static void netlink_free_old_listeners(struct rcu_head *rcu_head)

{

	struct listeners_rcu_head *lrh;



	lrh = container_of(rcu_head, struct listeners_rcu_head, rcu_head);

	kfree(lrh->ptr);

}



/**

/**

 * netlink_change_ngroups - change number of multicast groups

 * netlink_change_ngroups - change number of multicast groups

 *

 *
@@ -1516,6 +1530,7 @@ EXPORT_SYMBOL(netlink_kernel_release); 
int netlink_change_ngroups(struct sock *sk, unsigned int groups)

int netlink_change_ngroups(struct sock *sk, unsigned int groups)

{

{

	unsigned long *listeners, *old = NULL;

	unsigned long *listeners, *old = NULL;

	struct listeners_rcu_head *old_rcu_head;

	struct netlink_table *tbl = &nl_table[sk->sk_protocol];

	struct netlink_table *tbl = &nl_table[sk->sk_protocol];

	int err = 0;

	int err = 0;
@@ -1524,7 +1539,9 @@ int netlink_change_ngroups(struct sock *sk, unsigned int groups) 




	netlink_table_grab();

	netlink_table_grab();

	if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {

	if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {

		listeners = kzalloc(NLGRPSZ(groups), GFP_ATOMIC);

		listeners = kzalloc(NLGRPSZ(groups) +

				    sizeof(struct listeners_rcu_head),

				    GFP_ATOMIC);

		if (!listeners) {

		if (!listeners) {

			err = -ENOMEM;

			err = -ENOMEM;

			goto out_ungrab;

			goto out_ungrab;
@@ -1532,13 +1549,22 @@ int netlink_change_ngroups(struct sock *sk, unsigned int groups) 
		old = tbl->listeners;

		old = tbl->listeners;

		memcpy(listeners, old, NLGRPSZ(tbl->groups));

		memcpy(listeners, old, NLGRPSZ(tbl->groups));

		rcu_assign_pointer(tbl->listeners, listeners);

		rcu_assign_pointer(tbl->listeners, listeners);

		/*

		 * Free the old memory after an RCU grace period so we

		 * don't leak it. We use call_rcu() here in order to be

		 * able to call this function from atomic contexts. The

		 * allocation of this memory will have reserved enough

		 * space for struct listeners_rcu_head at the end.

		 */

		old_rcu_head = (void *)(tbl->listeners +

					NLGRPLONGS(tbl->groups));

		old_rcu_head->ptr = old;

		call_rcu(&old_rcu_head->rcu_head, netlink_free_old_listeners);

	}

	}

	tbl->groups = groups;

	tbl->groups = groups;





 out_ungrab:

 out_ungrab:

	netlink_table_ungrab();

	netlink_table_ungrab();

	synchronize_rcu();

	kfree(old);

	return err;

	return err;

}

}

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