[PATCH 6.18 401/752] ipv6: Move ipv6_fl_list from ipv6_pinfo to inet_sock.

Sasha Levin
2026-02-28T17:53:44Z

From: Kuniyuki Iwashima <kuniyu@google.com>

[ Upstream commit 1c17f4373d4db1e1f0ebd3ddcd8e7a642927a826 ]

In {tcp6,udp6,raw6}_sock, struct ipv6_pinfo is always placed at
the beginning of a new cache line because

1. __alignof__(struct tcp_sock) is 64 due to ____cacheline_aligned
of __cacheline_group_begin(tcp_sock_write_tx)

2. __alignof__(struct udp_sock) is 64 due to ____cacheline_aligned
of struct numa_drop_counters

3. in raw6_sock, struct numa_drop_counters is placed before
struct ipv6_pinfo

. struct ipv6_pinfo is 136 bytes, but the last cache line is
only used by ipv6_fl_list:

$ pahole -C ipv6_pinfo vmlinux
struct ipv6_pinfo {
...
/* --- cacheline 2 boundary (128 bytes) --- */
struct ipv6_fl_socklist * ipv6_fl_list; /* 128 8 */

/* size: 136, cachelines: 3, members: 23 */

Let's move ipv6_fl_list from struct ipv6_pinfo to struct inet_sock
to save a full cache line for {tcp6,udp6,raw6}_sock.

Now, struct ipv6_pinfo is 128 bytes, and {tcp6,udp6,raw6}_sock have
64 bytes less, while {tcp,udp,raw}_sock retain the same size.

Before:

# grep -E "^(RAW|UDP[^L\-]|TCP)" /proc/slabinfo | awk '{print $1, "\t", $4}'
RAWv6 1408
UDPv6 1472
TCPv6 2560
RAW 1152
UDP 1280
TCP 2368

After:

# grep -E "^(RAW|UDP[^L\-]|TCP)" /proc/slabinfo | awk '{print $1, "\t", $4}'
RAWv6 1344
UDPv6 1408
TCPv6 2496
RAW 1152
UDP 1280
TCP 2368

Also, ipv6_fl_list and inet_flags (SNDFLOW bit) are placed in the
same cache line.

$ pahole -C inet_sock vmlinux
...
/* --- cacheline 11 boundary (704 bytes) was 56 bytes ago --- */
struct ipv6_pinfo * pinet6; /* 760 8 */
/* --- cacheline 12 boundary (768 bytes) --- */
struct ipv6_fl_socklist * ipv6_fl_list; /* 768 8 */
unsigned long inet_flags; /* 776 8 */

Doc churn is due to the insufficient Type column (only 1 space short).

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251014224210.2964778-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 858d2a4f67ff ("tcp: fix potential race in tcp_v6_syn_recv_sock()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../networking/net_cachelines/inet_sock.rst | 79 ++++++++++---------
.../chelsio/inline_crypto/chtls/chtls_cm.c | 4 +-
include/linux/ipv6.h | 1 -
include/net/inet_sock.h | 1 +
net/ipv6/ip6_flowlabel.c | 44 +++++------
net/ipv6/tcp_ipv6.c | 13 +--
net/sctp/ipv6.c | 8 +-
7 files changed, 76 insertions(+), 74 deletions(-)

diff --git a/Documentation/networking/net_cachelines/inet_sock.rst b/Documentation/networking/net_cachelines/inet_sock.rst
index b11bf48fa2b36..4c72a28a7012e 100644
--- a/Documentation/networking/net_cachelines/inet_sock.rst
+++ b/Documentation/networking/net_cachelines/inet_sock.rst
@@ -5,42 +5,43 @@
inet_sock struct fast path usage breakdown
==========================================

-======================= ===================== =================== =================== ======================================================================================================
-Type Name fastpath_tx_access fastpath_rx_access comment
-======================= ===================== =================== =================== ======================================================================================================
-struct sock sk read_mostly read_mostly tcp_init_buffer_space,tcp_init_transfer,tcp_finish_connect,tcp_connect,tcp_send_rcvq,tcp_send_syn_data
-struct ipv6_pinfo* pinet6
-be16 inet_sport read_mostly __tcp_transmit_skb
-be32 inet_daddr read_mostly ip_select_ident_segs
-be32 inet_rcv_saddr
-be16 inet_dport read_mostly __tcp_transmit_skb
-u16 inet_num
-be32 inet_saddr
-s16 uc_ttl read_mostly __ip_queue_xmit/ip_select_ttl
-u16 cmsg_flags
-struct ip_options_rcu* inet_opt read_mostly __ip_queue_xmit
-u16 inet_id read_mostly ip_select_ident_segs
-u8 tos read_mostly ip_queue_xmit
-u8 min_ttl
-u8 mc_ttl
-u8 pmtudisc
-u8:1 recverr
-u8:1 is_icsk
-u8:1 freebind
-u8:1 hdrincl
-u8:1 mc_loop
-u8:1 transparent
-u8:1 mc_all
-u8:1 nodefrag
-u8:1 bind_address_no_port
-u8:1 recverr_rfc4884
-u8:1 defer_connect read_mostly tcp_sendmsg_fastopen
-u8 rcv_tos
-u8 convert_csum
-int uc_index
-int mc_index
-be32 mc_addr
-struct ip_mc_socklist* mc_list
-struct inet_cork_full cork read_mostly __tcp_transmit_skb
-struct local_port_range
-======================= ===================== =================== =================== ======================================================================================================
+======================== ===================== =================== =================== ======================================================================================================
+Type Name fastpath_tx_access fastpath_rx_access comment
+======================== ===================== =================== =================== ======================================================================================================
+struct sock sk read_mostly read_mostly tcp_init_buffer_space,tcp_init_transfer,tcp_finish_connect,tcp_connect,tcp_send_rcvq,tcp_send_syn_data
+struct ipv6_pinfo* pinet6
+struct ipv6_fl_socklist* ipv6_fl_list read_mostly tcp_v6_connect,__ip6_datagram_connect,udpv6_sendmsg,rawv6_sendmsg
+be16 inet_sport read_mostly __tcp_transmit_skb
+be32 inet_daddr read_mostly ip_select_ident_segs
+be32 inet_rcv_saddr
+be16 inet_dport read_mostly __tcp_transmit_skb
+u16 inet_num
+be32 inet_saddr
+s16 uc_ttl read_mostly __ip_queue_xmit/ip_select_ttl
+u16 cmsg_flags
+struct ip_options_rcu* inet_opt read_mostly __ip_queue_xmit
+u16 inet_id read_mostly ip_select_ident_segs
+u8 tos read_mostly ip_queue_xmit
+u8 min_ttl
+u8 mc_ttl
+u8 pmtudisc
+u8:1 recverr
+u8:1 is_icsk
+u8:1 freebind
+u8:1 hdrincl
+u8:1 mc_loop
+u8:1 transparent
+u8:1 mc_all
+u8:1 nodefrag
+u8:1 bind_address_no_port
+u8:1 recverr_rfc4884
+u8:1 defer_connect read_mostly tcp_sendmsg_fastopen
+u8 rcv_tos
+u8 convert_csum
+int uc_index
+int mc_index
+be32 mc_addr
+struct ip_mc_socklist* mc_list
+struct inet_cork_full cork read_mostly __tcp_transmit_skb
+struct local_port_range
+======================== ===================== =================== =================== ======================================================================================================
diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
index 4ee970f3bad6e..ee0154337a9c5 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
@@ -1199,12 +1199,12 @@ static struct sock *chtls_recv_sock(struct sock *lsk,
struct ipv6_pinfo *newnp = inet6_sk(newsk);
struct ipv6_pinfo *np = inet6_sk(lsk);

- inet_sk(newsk)->pinet6 = &newtcp6sk->inet6;
+ newinet->pinet6 = &newtcp6sk->inet6;
+ newinet->ipv6_fl_list = NULL;
memcpy(newnp, np, sizeof(struct ipv6_pinfo));
newsk->sk_v6_daddr = treq->ir_v6_rmt_addr;
newsk->sk_v6_rcv_saddr = treq->ir_v6_loc_addr;
inet6_sk(newsk)->saddr = treq->ir_v6_loc_addr;
- newnp->ipv6_fl_list = NULL;
newnp->pktoptions = NULL;
newsk->sk_bound_dev_if = treq->ir_iif;
newinet->inet_opt = NULL;
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 43b7bb8287388..7294e4e89b797 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -271,7 +271,6 @@ struct ipv6_pinfo {

struct ipv6_mc_socklist __rcu *ipv6_mc_list;
struct ipv6_ac_socklist *ipv6_ac_list;
- struct ipv6_fl_socklist __rcu *ipv6_fl_list;
};

/* We currently use available bits from inet_sk(sk)->inet_flags,
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 1086256549faa..b6ec08072533a 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -214,6 +214,7 @@ struct inet_sock {
struct sock sk;
#if IS_ENABLED(CONFIG_IPV6)
struct ipv6_pinfo *pinet6;
+ struct ipv6_fl_socklist __rcu *ipv6_fl_list;
#endif
/* Socket demultiplex comparisons on incoming packets. */
#define inet_daddr sk.__sk_common.skc_daddr
diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
index a3ff575798dda..60d0be47a9f31 100644
--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -66,8 +66,8 @@ EXPORT_SYMBOL(ipv6_flowlabel_exclusive);
fl != NULL; \
fl = rcu_dereference(fl->next))

-#define for_each_sk_fl_rcu(np, sfl) \
- for (sfl = rcu_dereference(np->ipv6_fl_list); \
+#define for_each_sk_fl_rcu(sk, sfl) \
+ for (sfl = rcu_dereference(inet_sk(sk)->ipv6_fl_list); \
sfl != NULL; \
sfl = rcu_dereference(sfl->next))

@@ -262,12 +262,11 @@ static struct ip6_flowlabel *fl_intern(struct net *net,
struct ip6_flowlabel *__fl6_sock_lookup(struct sock *sk, __be32 label)
{
struct ipv6_fl_socklist *sfl;
- struct ipv6_pinfo *np = inet6_sk(sk);

label &= IPV6_FLOWLABEL_MASK;

rcu_read_lock();
- for_each_sk_fl_rcu(np, sfl) {
+ for_each_sk_fl_rcu(sk, sfl) {
struct ip6_flowlabel *fl = sfl->fl;

if (fl->label == label && atomic_inc_not_zero(&fl->users)) {
@@ -283,16 +282,16 @@ EXPORT_SYMBOL_GPL(__fl6_sock_lookup);

void fl6_free_socklist(struct sock *sk)
{
- struct ipv6_pinfo *np = inet6_sk(sk);
+ struct inet_sock *inet = inet_sk(sk);
struct ipv6_fl_socklist *sfl;

- if (!rcu_access_pointer(np->ipv6_fl_list))
+ if (!rcu_access_pointer(inet->ipv6_fl_list))
return;

spin_lock_bh(&ip6_sk_fl_lock);
- while ((sfl = rcu_dereference_protected(np->ipv6_fl_list,
+ while ((sfl = rcu_dereference_protected(inet->ipv6_fl_list,
lockdep_is_held(&ip6_sk_fl_lock))) != NULL) {
- np->ipv6_fl_list = sfl->next;
+ inet->ipv6_fl_list = sfl->next;
spin_unlock_bh(&ip6_sk_fl_lock);

fl_release(sfl->fl);
@@ -470,16 +469,15 @@ fl_create(struct net *net, struct sock *sk, struct in6_flowlabel_req *freq,

static int mem_check(struct sock *sk)
{
- struct ipv6_pinfo *np = inet6_sk(sk);
- struct ipv6_fl_socklist *sfl;
int room = FL_MAX_SIZE - atomic_read(&fl_size);
+ struct ipv6_fl_socklist *sfl;
int count = 0;

if (room > FL_MAX_SIZE - FL_MAX_PER_SOCK)
return 0;

rcu_read_lock();
- for_each_sk_fl_rcu(np, sfl)
+ for_each_sk_fl_rcu(sk, sfl)
count++;
rcu_read_unlock();

@@ -492,13 +490,15 @@ static int mem_check(struct sock *sk)
return 0;
}

-static inline void fl_link(struct ipv6_pinfo *np, struct ipv6_fl_socklist *sfl,
- struct ip6_flowlabel *fl)
+static inline void fl_link(struct sock *sk, struct ipv6_fl_socklist *sfl,
+ struct ip6_flowlabel *fl)
{
+ struct inet_sock *inet = inet_sk(sk);
+
spin_lock_bh(&ip6_sk_fl_lock);
sfl->fl = fl;
- sfl->next = np->ipv6_fl_list;
- rcu_assign_pointer(np->ipv6_fl_list, sfl);
+ sfl->next = inet->ipv6_fl_list;
+ rcu_assign_pointer(inet->ipv6_fl_list, sfl);
spin_unlock_bh(&ip6_sk_fl_lock);
}

@@ -520,7 +520,7 @@ int ipv6_flowlabel_opt_get(struct sock *sk, struct in6_flowlabel_req *freq,

rcu_read_lock();

- for_each_sk_fl_rcu(np, sfl) {
+ for_each_sk_fl_rcu(sk, sfl) {
if (sfl->fl->label == (np->flow_label & IPV6_FLOWLABEL_MASK)) {
spin_lock_bh(&ip6_fl_lock);
freq->flr_label = sfl->fl->label;
@@ -559,7 +559,7 @@ static int ipv6_flowlabel_put(struct sock *sk, struct in6_flowlabel_req *freq)
}

spin_lock_bh(&ip6_sk_fl_lock);
- for (sflp = &np->ipv6_fl_list;
+ for (sflp = &inet_sk(sk)->ipv6_fl_list;
(sfl = socklist_dereference(*sflp)) != NULL;
sflp = &sfl->next) {
if (sfl->fl->label == freq->flr_label)
@@ -579,13 +579,12 @@ static int ipv6_flowlabel_put(struct sock *sk, struct in6_flowlabel_req *freq)

static int ipv6_flowlabel_renew(struct sock *sk, struct in6_flowlabel_req *freq)
{
- struct ipv6_pinfo *np = inet6_sk(sk);
struct net *net = sock_net(sk);
struct ipv6_fl_socklist *sfl;
int err;

rcu_read_lock();
- for_each_sk_fl_rcu(np, sfl) {
+ for_each_sk_fl_rcu(sk, sfl) {
if (sfl->fl->label == freq->flr_label) {
err = fl6_renew(sfl->fl, freq->flr_linger,
freq->flr_expires);
@@ -614,7 +613,6 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
{
struct ipv6_fl_socklist *sfl, *sfl1 = NULL;
struct ip6_flowlabel *fl, *fl1 = NULL;
- struct ipv6_pinfo *np = inet6_sk(sk);
struct net *net = sock_net(sk);
int err;

@@ -645,7 +643,7 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
if (freq->flr_label) {
err = -EEXIST;
rcu_read_lock();
- for_each_sk_fl_rcu(np, sfl) {
+ for_each_sk_fl_rcu(sk, sfl) {
if (sfl->fl->label == freq->flr_label) {
if (freq->flr_flags & IPV6_FL_F_EXCL) {
rcu_read_unlock();
@@ -682,7 +680,7 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
fl1->linger = fl->linger;
if ((long)(fl->expires - fl1->expires) > 0)
fl1->expires = fl->expires;
- fl_link(np, sfl1, fl1);
+ fl_link(sk, sfl1, fl1);
fl_free(fl);
return 0;

@@ -716,7 +714,7 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
}
}

- fl_link(np, sfl1, fl);
+ fl_link(sk, sfl1, fl);
return 0;
done:
fl_free(fl);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 2e07dba293b41..0937d69658310 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1387,7 +1387,9 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
if (!newsk)
return NULL;

- inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
+ newinet = inet_sk(newsk);
+ newinet->pinet6 = tcp_inet6_sk(newsk);
+ newinet->ipv6_fl_list = NULL;

newnp = tcp_inet6_sk(newsk);
newtp = tcp_sk(newsk);
@@ -1406,7 +1408,6 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *

newnp->ipv6_mc_list = NULL;
newnp->ipv6_ac_list = NULL;
- newnp->ipv6_fl_list = NULL;
newnp->pktoptions = NULL;
newnp->opt = NULL;
newnp->mcast_oif = inet_iif(skb);
@@ -1454,10 +1455,12 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
newsk->sk_gso_type = SKB_GSO_TCPV6;
inet6_sk_rx_dst_set(newsk, skb);

- inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
+ newinet = inet_sk(newsk);
+ newinet->pinet6 = tcp_inet6_sk(newsk);
+ newinet->ipv6_fl_list = NULL;
+ newinet->inet_opt = NULL;

newtp = tcp_sk(newsk);
- newinet = inet_sk(newsk);
newnp = tcp_inet6_sk(newsk);

memcpy(newnp, np, sizeof(struct ipv6_pinfo));
@@ -1470,10 +1473,8 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *

First: no IPv4 options.
*/
- newinet->inet_opt = NULL;
newnp->ipv6_mc_list = NULL;
newnp->ipv6_ac_list = NULL;
- newnp->ipv6_fl_list = NULL;

/* Clone RX bits */
newnp->rxopt.all = np->rxopt.all;
diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index 568ff8797c393..d725b21587588 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -782,9 +782,10 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
struct sctp_association *asoc,
bool kern)
{
- struct sock *newsk;
struct ipv6_pinfo *newnp, *np = inet6_sk(sk);
struct sctp6_sock *newsctp6sk;
+ struct inet_sock *newinet;
+ struct sock *newsk;

newsk = sk_alloc(sock_net(sk), PF_INET6, GFP_KERNEL, sk->sk_prot, kern);
if (!newsk)
@@ -796,7 +797,9 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
sock_reset_flag(sk, SOCK_ZAPPED);

newsctp6sk = (struct sctp6_sock *)newsk;
- inet_sk(newsk)->pinet6 = &newsctp6sk->inet6;
+ newinet = inet_sk(newsk);
+ newinet->pinet6 = &newsctp6sk->inet6;
+ newinet->ipv6_fl_list = NULL;

sctp_sk(newsk)->v4mapped = sctp_sk(sk)->v4mapped;

@@ -805,7 +808,6 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
memcpy(newnp, np, sizeof(struct ipv6_pinfo));
newnp->ipv6_mc_list = NULL;
newnp->ipv6_ac_list = NULL;
- newnp->ipv6_fl_list = NULL;

sctp_v6_copy_ip_options(sk, newsk);

--
2.51.0