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net: add SOCK_RCU_FREE socket flag 

We want a generic way to insert an RCU grace period before socket
freeing for cases where RCU_SLAB_DESTROY_BY_RCU is adding too
much overhead.

SLAB_DESTROY_BY_RCU strict rules force us to take a reference
on the socket sk_refcnt, and it is a performance problem for UDP
encapsulation, or TCP synflood behavior, as many CPUs might
attempt the atomic operations on a shared sk_refcnt

UDP sockets and TCP listeners can set SOCK_RCU_FREE so that their
lookup can use traditional RCU rules, without refcount changes.
They can set the flag only once hashed and visible by other cpus.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Tested-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
hifive-unleashed-5.1
Eric Dumazet 2016-04-01 08:52:12 -07:00 committed by David S. Miller
parent 43e2dfb23e
commit a4298e4522
2 changed files with 15 additions and 1 deletions
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2
include/net/sock.h
View File

@ -438,6 +438,7 @@ struct sock {
struct sk_buff *skb);
void (*sk_destruct)(struct sock *sk);
struct sock_reuseport __rcu *sk_reuseport_cb;
struct rcu_head sk_rcu;
};
#define __sk_user_data(sk) ((*((void __rcu **)&(sk)->sk_user_data)))
@ -720,6 +721,7 @@ enum sock_flags {
*/
SOCK_FILTER_LOCKED, /* Filter cannot be changed anymore */
SOCK_SELECT_ERR_QUEUE, /* Wake select on error queue */
SOCK_RCU_FREE, /* wait rcu grace period in sk_destruct() */
};
#define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))

14
net/core/sock.c
View File

@ -1419,8 +1419,12 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
}
EXPORT_SYMBOL(sk_alloc);
void sk_destruct(struct sock *sk)
/* Sockets having SOCK_RCU_FREE will call this function after one RCU
* grace period. This is the case for UDP sockets and TCP listeners.
*/
static void __sk_destruct(struct rcu_head *head)
{
struct sock *sk = container_of(head, struct sock, sk_rcu);
struct sk_filter *filter;
if (sk->sk_destruct)
@ -1449,6 +1453,14 @@ void sk_destruct(struct sock *sk)
sk_prot_free(sk->sk_prot_creator, sk);
}
void sk_destruct(struct sock *sk)
{
if (sock_flag(sk, SOCK_RCU_FREE))
call_rcu(&sk->sk_rcu, __sk_destruct);
else
__sk_destruct(&sk->sk_rcu);
}
static void __sk_free(struct sock *sk)
{
if (unlikely(sock_diag_has_destroy_listeners(sk) && sk->sk_net_refcnt))