From 052ada096842a910327936b4ed203048906eb2c3 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Thu, 28 Apr 2022 11:58:18 +0100 Subject: 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: Pavel Begunkov Signed-off-by: David S. Miller --- net/core/sock.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/net/core/sock.c b/net/core/sock.c index 6ad22fc2eb81..ab865b04130b 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -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 -- cgit v1.2.3-59-g8ed1b