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Date: Mon, 11 Dec 2017 21:25:12 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] tcp/dccp: avoid one atomic operation for timewait
hashdance
From: Eric Dumazet <edumazet@...gle.com>
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@...gle.com>
---
include/net/inet_timewait_sock.h | 4 ++--
net/dccp/minisocks.c | 7 ++++---
net/ipv4/inet_timewait_sock.c | 27 +++++++++++++--------------
net/ipv4/tcp_minisocks.c | 7 ++++---
4 files changed, 23 insertions(+), 22 deletions(-)
diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index 1356fa6a7566bf8b53632215ef8de4b153848f9b..899495589a7ea2bf693cdda42f83cec160e861b5 100644
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -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);
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index 178bb9833311f83205317b07fe64cb2e45a9f734..37ccbe62eb1af3f9dffbf63323c008cc96cd8ea1 100644
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -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
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index b563e0c46bac2362acccf38495546a8b6b726384..277ff69a312dca1d0bc04be4b0b36db133aaf63b 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -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)
{
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b079b619b60ca577d5ef20a5065fce87acecd96c..a8384b0c11f8fa589e2ed5311899b62c80a269f8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -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
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