Commit 052ada09 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by David S. Miller
Browse files

sock: optimise UDP sock_wfree() refcounting 



For non SOCK_USE_WRITE_QUEUE sockets, sock_wfree() (atomically) puts
->sk_wmem_alloc twice. It's needed to keep the socket alive while
calling ->sk_write_space() after the first put.

However, some sockets, such as UDP, are freed by RCU
(i.e. SOCK_RCU_FREE) and use already RCU-safe sock_def_write_space().
Carve a fast path for such sockets, put down all refs in one go before
calling sock_def_write_space() but guard the socket from being freed
by an RCU read section.

note: because TCP sockets are marked with SOCK_USE_WRITE_QUEUE it
doesn't add extra checks in its path.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 14bfee9b

net/core/sock.c

+14 −0
Original line number Diff line number Diff line
@@ -146,6 +146,8 @@ 
static DEFINE_MUTEX(proto_list_mutex);

static LIST_HEAD(proto_list);



static void sock_def_write_space(struct sock *sk);



/**

 * sk_ns_capable - General socket capability test

 * @sk: Socket to use a capability on or through
@@ -2324,8 +2326,20 @@ void sock_wfree(struct sk_buff *skb) 
{

	struct sock *sk = skb->sk;

	unsigned int len = skb->truesize;

	bool free;



	if (!sock_flag(sk, SOCK_USE_WRITE_QUEUE)) {

		if (sock_flag(sk, SOCK_RCU_FREE) &&

		    sk->sk_write_space == sock_def_write_space) {

			rcu_read_lock();

			free = refcount_sub_and_test(len, &sk->sk_wmem_alloc);

			sock_def_write_space(sk);

			rcu_read_unlock();

			if (unlikely(free))

				__sk_free(sk);

			return;

		}



		/*

		 * Keep a reference on sk_wmem_alloc, this will be released

		 * after sk_write_space() call