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netlink: use call_rcu for netlink_change_ngroups

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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: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Johannes Berg 2009-07-10 09:51:32 +00:00 • committed by David S. Miller
commit 6c04bb18dd
1 changed files with 30 additions and 4 deletions
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34
net/netlink/af_netlink.c
View file

@ -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;
} }