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sock: optimise UDP sock_wfree() refcounting

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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 <asml.silence@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Pavel Begunkov 2022-04-28 11:58:18 +01:00 committed by David S. Miller
parent 14bfee9b62
commit 052ada0968
1 changed files with 14 additions and 0 deletions
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14
net/core/sock.c
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@ -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