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netlink: Lockless lookup with RCU grace period in socket release 

Defers the release of the socket reference using call_rcu() to
allow using an RCU read-side protected call to rhashtable_lookup()

This restores behaviour and performance gains as previously
introduced by e341694 ("netlink: Convert netlink_lookup() to use
RCU protected hash table") without the side effect of severely
delayed socket destruction.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Thomas Graf 2015-01-02 23:00:22 +01:00 committed by David S. Miller
parent f89bd6f87a
commit 21e4902aea
2 changed files with 17 additions and 16 deletions
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32
net/netlink/af_netlink.c
View File

@ -97,12 +97,12 @@ static int netlink_dump(struct sock *sk);
static void netlink_skb_destructor(struct sk_buff *skb);
/* nl_table locking explained:
* Lookup and traversal are protected with nl_sk_hash_lock or nl_table_lock
* combined with an RCU read-side lock. Insertion and removal are protected
* with nl_sk_hash_lock while using RCU list modification primitives and may
* run in parallel to nl_table_lock protected lookups. Destruction of the
* Netlink socket may only occur *after* nl_table_lock has been acquired
* either during or after the socket has been removed from the list.
* Lookup and traversal are protected with an RCU read-side lock. Insertion
* and removal are protected with nl_sk_hash_lock while using RCU list
* modification primitives and may run in parallel to RCU protected lookups.
* Destruction of the Netlink socket may only occur *after* nl_table_lock has
* been acquired * either during or after the socket has been removed from
* the list and after an RCU grace period.
*/
DEFINE_RWLOCK(nl_table_lock);
EXPORT_SYMBOL_GPL(nl_table_lock);
@ -1003,13 +1003,11 @@ static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
struct netlink_table *table = &nl_table[protocol];
struct sock *sk;
read_lock(&nl_table_lock);
rcu_read_lock();
sk = __netlink_lookup(table, portid, net);
if (sk)
sock_hold(sk);
rcu_read_unlock();
read_unlock(&nl_table_lock);
return sk;
}
@ -1183,6 +1181,13 @@ out_module:
goto out;
}
static void deferred_put_nlk_sk(struct rcu_head *head)
{
struct netlink_sock *nlk = container_of(head, struct netlink_sock, rcu);
sock_put(&nlk->sk);
}
static int netlink_release(struct socket *sock)
{
struct sock *sk = sock->sk;
@ -1248,7 +1253,7 @@ static int netlink_release(struct socket *sock)
local_bh_disable();
sock_prot_inuse_add(sock_net(sk), &netlink_proto, -1);
local_bh_enable();
sock_put(sk);
call_rcu(&nlk->rcu, deferred_put_nlk_sk);
return 0;
}
@ -1263,7 +1268,6 @@ static int netlink_autobind(struct socket *sock)
retry:
cond_resched();
netlink_table_grab();
rcu_read_lock();
if (__netlink_lookup(table, portid, net)) {
/* Bind collision, search negative portid values. */
@ -1271,11 +1275,9 @@ retry:
if (rover > -4097)
rover = -4097;
rcu_read_unlock();
netlink_table_ungrab();
goto retry;
}
rcu_read_unlock();
netlink_table_ungrab();
err = netlink_insert(sk, net, portid);
if (err == -EADDRINUSE)
@ -2910,9 +2912,8 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
}
static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
__acquires(nl_table_lock) __acquires(RCU)
__acquires(RCU)
{
read_lock(&nl_table_lock);
rcu_read_lock();
return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
}
@ -2964,10 +2965,9 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
}
static void netlink_seq_stop(struct seq_file *seq, void *v)
__releases(RCU) __releases(nl_table_lock)
__releases(RCU)
{
rcu_read_unlock();
read_unlock(&nl_table_lock);
}

1
net/netlink/af_netlink.h
View File

@ -50,6 +50,7 @@ struct netlink_sock {
#endif /* CONFIG_NETLINK_MMAP */
struct rhash_head node;
struct rcu_head rcu;
};
static inline struct netlink_sock *nlk_sk(struct sock *sk)