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authorJohannes Berg <johannes@sipsolutions.net>2009-07-10 09:51:32 +0000
committerDavid S. Miller <davem@davemloft.net>2009-07-12 14:03:24 -0700
commit6c04bb18ddd633b7feac2c8fe2ae0bf61d20ca7a (patch)
treed80582a2c3c248acef1193291a1888ffd588e9fd /net
parent487420df79f1d9f5b9de74c9bef378609c475a39 (diff)
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: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/netlink/af_netlink.c34
1 files changed, 30 insertions, 4 deletions
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index d7d1b822e824..d46da6cb92e4 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -83,6 +83,11 @@ struct netlink_sock {
struct module *module;
};
+struct listeners_rcu_head {
+ struct rcu_head rcu_head;
+ void *ptr;
+};
+
#define NETLINK_KERNEL_SOCKET 0x1
#define NETLINK_RECV_PKTINFO 0x2
#define NETLINK_BROADCAST_SEND_ERROR 0x4
@@ -1453,7 +1458,8 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
if (groups < 32)
groups = 32;
- listeners = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
+ listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head),
+ GFP_KERNEL);
if (!listeners)
goto out_sock_release;
@@ -1501,6 +1507,14 @@ netlink_kernel_release(struct sock *sk)
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
*
@@ -1516,6 +1530,7 @@ EXPORT_SYMBOL(netlink_kernel_release);
int netlink_change_ngroups(struct sock *sk, unsigned int groups)
{
unsigned long *listeners, *old = NULL;
+ struct listeners_rcu_head *old_rcu_head;
struct netlink_table *tbl = &nl_table[sk->sk_protocol];
int err = 0;
@@ -1524,7 +1539,9 @@ int netlink_change_ngroups(struct sock *sk, unsigned int groups)
netlink_table_grab();
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) {
err = -ENOMEM;
goto out_ungrab;
@@ -1532,13 +1549,22 @@ int netlink_change_ngroups(struct sock *sk, unsigned int groups)
old = tbl->listeners;
memcpy(listeners, old, NLGRPSZ(tbl->groups));
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;
out_ungrab:
netlink_table_ungrab();
- synchronize_rcu();
- kfree(old);
return err;
}