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Commit ec94c269 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp/dccp: avoid one atomic operation for timewait hashdance 



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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1e757011

include/net/inet_timewait_sock.h

+2 −2
Original line number Diff line number Diff line
@@ -93,7 +93,7 @@ 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,

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,

net/dccp/minisocks.c

+4 −3
Original line number Diff line number Diff line
@@ -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

net/ipv4/inet_timewait_sock.c

+13 −14
Original line number Diff line number Diff line
@@ -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)

{

net/ipv4/tcp_minisocks.c

+4 −3
Original line number Diff line number Diff line
@@ -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