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tcp/dccp: avoid one atomic operation for timewait hashdance

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First, rename __inet_twsk_hashdance() to inet_twsk_hashdance()

Then, remove one inet_twsk_put() by setting tw_refcnt to 3 instead
of 4, but adding a fat warning that we do not have the right to access
tw anymore after inet_twsk_hashdance()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-12-11 21:25:12 -08:00 committed by David S. Miller
parent 1e75701175
commit ec94c2696f
4 changed files with 23 additions and 22 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

4
include/net/inet_timewait_sock.h
View file

@ -93,8 +93,8 @@ struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
struct inet_timewait_death_row *dr,
const int state);
void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
struct inet_hashinfo *hashinfo);
void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
struct inet_hashinfo *hashinfo);
void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo,
bool rearm);

7
net/dccp/minisocks.c
View file

@ -63,9 +63,10 @@ void dccp_time_wait(struct sock *sk, int state, int timeo)
*/
local_bh_disable();
inet_twsk_schedule(tw, timeo);
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
inet_twsk_put(tw);
/* Linkage updates.
* Note that access to tw after this point is illegal.
*/
inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
local_bh_enable();
} else {
/* Sorry, if we're out of memory, just CLOSE this

27
net/ipv4/inet_timewait_sock.c
View file

@ -97,7 +97,7 @@ static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
* Essentially we whip up a timewait bucket, copy the relevant info into it
* from the SK, and mess with hash chains and list linkage.
*/
void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
struct inet_hashinfo *hashinfo)
{
const struct inet_sock *inet = inet_sk(sk);
@ -119,18 +119,6 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
spin_lock(lock);
/*
* Step 2: Hash TW into tcp ehash chain.
* Notes :
* - tw_refcnt is set to 4 because :
* - We have one reference from bhash chain.
* - We have one reference from ehash chain.
* - We have one reference from timer.
* - One reference for ourself (our caller will release it).
* We can use atomic_set() because prior spin_lock()/spin_unlock()
* committed into memory all tw fields.
*/
refcount_set(&tw->tw_refcnt, 4);
inet_twsk_add_node_rcu(tw, &ehead->chain);
/* Step 3: Remove SK from hash chain */
@ -138,8 +126,19 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
spin_unlock(lock);
/* tw_refcnt is set to 3 because we have :
* - one reference for bhash chain.
* - one reference for ehash chain.
* - one reference for timer.
* We can use atomic_set() because prior spin_lock()/spin_unlock()
* committed into memory all tw fields.
* Also note that after this point, we lost our implicit reference
* so we are not allowed to use tw anymore.
*/
refcount_set(&tw->tw_refcnt, 3);
}
EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);
EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
static void tw_timer_handler(struct timer_list *t)
{

7
net/ipv4/tcp_minisocks.c
View file

@ -316,9 +316,10 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
*/
local_bh_disable();
inet_twsk_schedule(tw, timeo);
/* Linkage updates. */
__inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
inet_twsk_put(tw);
/* Linkage updates.
* Note that access to tw after this point is illegal.
*/
inet_twsk_hashdance(tw, sk, &tcp_hashinfo);
local_bh_enable();
} else {
/* Sorry, if we're out of memory, just CLOSE this