net: sk_dst_cache RCUification
With latest CONFIG_PROVE_RCU stuff, I felt more comfortable to make this
work.
sk->sk_dst_cache is currently protected by a rwlock (sk_dst_lock)
This rwlock is readlocked for a very small amount of time, and dst
entries are already freed after RCU grace period. This calls for RCU
again :)
This patch converts sk_dst_lock to a spinlock, and use RCU for readers.
__sk_dst_get() is supposed to be called with rcu_read_lock() or if
socket locked by user, so use appropriate rcu_dereference_check()
condition (rcu_read_lock_held() || sock_owned_by_user(sk))
This patch avoids two atomic ops per tx packet on UDP connected sockets,
for example, and permits sk_dst_lock to be much less dirtied.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
index b4603cd..56df440 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -262,7 +262,7 @@
#ifdef CONFIG_XFRM
struct xfrm_policy *sk_policy[2];
#endif
- rwlock_t sk_dst_lock;
+ spinlock_t sk_dst_lock;
atomic_t sk_rmem_alloc;
atomic_t sk_wmem_alloc;
atomic_t sk_omem_alloc;
@@ -1192,7 +1192,8 @@
static inline struct dst_entry *
__sk_dst_get(struct sock *sk)
{
- return sk->sk_dst_cache;
+ return rcu_dereference_check(sk->sk_dst_cache, rcu_read_lock_held() ||
+ sock_owned_by_user(sk));
}
static inline struct dst_entry *
@@ -1200,50 +1201,62 @@
{
struct dst_entry *dst;
- read_lock(&sk->sk_dst_lock);
- dst = sk->sk_dst_cache;
+ rcu_read_lock();
+ dst = rcu_dereference(sk->sk_dst_cache);
if (dst)
dst_hold(dst);
- read_unlock(&sk->sk_dst_lock);
+ rcu_read_unlock();
return dst;
}
+extern void sk_reset_txq(struct sock *sk);
+
+static inline void dst_negative_advice(struct sock *sk)
+{
+ struct dst_entry *ndst, *dst = __sk_dst_get(sk);
+
+ if (dst && dst->ops->negative_advice) {
+ ndst = dst->ops->negative_advice(dst);
+
+ if (ndst != dst) {
+ rcu_assign_pointer(sk->sk_dst_cache, ndst);
+ sk_reset_txq(sk);
+ }
+ }
+}
+
static inline void
__sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
struct dst_entry *old_dst;
sk_tx_queue_clear(sk);
- old_dst = sk->sk_dst_cache;
- sk->sk_dst_cache = dst;
+ old_dst = rcu_dereference_check(sk->sk_dst_cache,
+ lockdep_is_held(&sk->sk_dst_lock));
+ rcu_assign_pointer(sk->sk_dst_cache, dst);
dst_release(old_dst);
}
static inline void
sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
- write_lock(&sk->sk_dst_lock);
+ spin_lock(&sk->sk_dst_lock);
__sk_dst_set(sk, dst);
- write_unlock(&sk->sk_dst_lock);
+ spin_unlock(&sk->sk_dst_lock);
}
static inline void
__sk_dst_reset(struct sock *sk)
{
- struct dst_entry *old_dst;
-
- sk_tx_queue_clear(sk);
- old_dst = sk->sk_dst_cache;
- sk->sk_dst_cache = NULL;
- dst_release(old_dst);
+ __sk_dst_set(sk, NULL);
}
static inline void
sk_dst_reset(struct sock *sk)
{
- write_lock(&sk->sk_dst_lock);
+ spin_lock(&sk->sk_dst_lock);
__sk_dst_reset(sk);
- write_unlock(&sk->sk_dst_lock);
+ spin_unlock(&sk->sk_dst_lock);
}
extern struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie);