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/net/core/dev.c b/net/core/dev.c
index 0eb79e3..ca4cdef 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2015,7 +2015,7 @@
if (dev->real_num_tx_queues > 1)
queue_index = skb_tx_hash(dev, skb);
- if (sk && sk->sk_dst_cache)
+ if (sk && rcu_dereference_check(sk->sk_dst_cache, 1))
sk_tx_queue_set(sk, queue_index);
}
}