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Message-ID: <20250826023346.26046-1-dqfext@gmail.com>
Date: Tue, 26 Aug 2025 10:33:44 +0800
From: Qingfang Deng <dqfext@...il.com>
To: Michal Ostrowski <mostrows@...thlink.net>,
Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH net-next 1/2] pppoe: remove rwlock usage
Like ppp_generic.c, convert the PPPoE socket hash table to use RCU for
lookups and a spinlock for updates. This removes rwlock usage and allows
lockless readers on the fast path.
- Mark hash table and list pointers as __rcu.
- Use spin_lock() to protect writers.
- Readers use rcu_dereference() under rcu_read_lock(). All known callers
of get_item() already hold the RCU read lock, so no additional locking
is needed.
- Set SOCK_RCU_FREE to defer socket freeing until after an RCU grace
period.
Signed-off-by: Qingfang Deng <dqfext@...il.com>
---
drivers/net/ppp/pppoe.c | 83 ++++++++++++++++++++++------------------
include/linux/if_pppox.h | 2 +-
2 files changed, 46 insertions(+), 39 deletions(-)
diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index 410effa42ade..f99533c80b66 100644
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -100,8 +100,8 @@ struct pppoe_net {
* as well, moreover in case of SMP less locking
* controversy here
*/
- struct pppox_sock *hash_table[PPPOE_HASH_SIZE];
- rwlock_t hash_lock;
+ struct pppox_sock __rcu *hash_table[PPPOE_HASH_SIZE];
+ spinlock_t hash_lock;
};
/*
@@ -162,13 +162,13 @@ static struct pppox_sock *__get_item(struct pppoe_net *pn, __be16 sid,
int hash = hash_item(sid, addr);
struct pppox_sock *ret;
- ret = pn->hash_table[hash];
+ ret = rcu_dereference(pn->hash_table[hash]);
while (ret) {
if (cmp_addr(&ret->pppoe_pa, sid, addr) &&
ret->pppoe_ifindex == ifindex)
return ret;
- ret = ret->next;
+ ret = rcu_dereference(ret->next);
}
return NULL;
@@ -177,19 +177,20 @@ static struct pppox_sock *__get_item(struct pppoe_net *pn, __be16 sid,
static int __set_item(struct pppoe_net *pn, struct pppox_sock *po)
{
int hash = hash_item(po->pppoe_pa.sid, po->pppoe_pa.remote);
- struct pppox_sock *ret;
+ struct pppox_sock *ret, *first;
- ret = pn->hash_table[hash];
+ first = rcu_dereference_protected(pn->hash_table[hash], lockdep_is_held(&pn->hash_lock));
+ ret = first;
while (ret) {
if (cmp_2_addr(&ret->pppoe_pa, &po->pppoe_pa) &&
ret->pppoe_ifindex == po->pppoe_ifindex)
return -EALREADY;
- ret = ret->next;
+ ret = rcu_dereference_protected(ret->next, lockdep_is_held(&pn->hash_lock));
}
- po->next = pn->hash_table[hash];
- pn->hash_table[hash] = po;
+ RCU_INIT_POINTER(po->next, first);
+ rcu_assign_pointer(pn->hash_table[hash], po);
return 0;
}
@@ -198,20 +199,24 @@ static void __delete_item(struct pppoe_net *pn, __be16 sid,
char *addr, int ifindex)
{
int hash = hash_item(sid, addr);
- struct pppox_sock *ret, **src;
+ struct pppox_sock *ret, __rcu **src;
- ret = pn->hash_table[hash];
+ ret = rcu_dereference_protected(pn->hash_table[hash], lockdep_is_held(&pn->hash_lock));
src = &pn->hash_table[hash];
while (ret) {
if (cmp_addr(&ret->pppoe_pa, sid, addr) &&
ret->pppoe_ifindex == ifindex) {
- *src = ret->next;
+ struct pppox_sock *next;
+
+ next = rcu_dereference_protected(ret->next,
+ lockdep_is_held(&pn->hash_lock));
+ rcu_assign_pointer(*src, next);
break;
}
src = &ret->next;
- ret = ret->next;
+ ret = rcu_dereference_protected(ret->next, lockdep_is_held(&pn->hash_lock));
}
}
@@ -225,11 +230,9 @@ static inline struct pppox_sock *get_item(struct pppoe_net *pn, __be16 sid,
{
struct pppox_sock *po;
- read_lock_bh(&pn->hash_lock);
po = __get_item(pn, sid, addr, ifindex);
if (po)
sock_hold(sk_pppox(po));
- read_unlock_bh(&pn->hash_lock);
return po;
}
@@ -258,9 +261,9 @@ static inline struct pppox_sock *get_item_by_addr(struct net *net,
static inline void delete_item(struct pppoe_net *pn, __be16 sid,
char *addr, int ifindex)
{
- write_lock_bh(&pn->hash_lock);
+ spin_lock(&pn->hash_lock);
__delete_item(pn, sid, addr, ifindex);
- write_unlock_bh(&pn->hash_lock);
+ spin_unlock(&pn->hash_lock);
}
/***************************************************************************
@@ -276,14 +279,16 @@ static void pppoe_flush_dev(struct net_device *dev)
int i;
pn = pppoe_pernet(dev_net(dev));
- write_lock_bh(&pn->hash_lock);
+ spin_lock(&pn->hash_lock);
for (i = 0; i < PPPOE_HASH_SIZE; i++) {
- struct pppox_sock *po = pn->hash_table[i];
+ struct pppox_sock *po = rcu_dereference_protected(pn->hash_table[i],
+ lockdep_is_held(&pn->hash_lock));
struct sock *sk;
while (po) {
while (po && po->pppoe_dev != dev) {
- po = po->next;
+ po = rcu_dereference_protected(po->next,
+ lockdep_is_held(&pn->hash_lock));
}
if (!po)
@@ -300,7 +305,7 @@ static void pppoe_flush_dev(struct net_device *dev)
*/
sock_hold(sk);
- write_unlock_bh(&pn->hash_lock);
+ spin_unlock(&pn->hash_lock);
lock_sock(sk);
if (po->pppoe_dev == dev &&
@@ -320,11 +325,12 @@ static void pppoe_flush_dev(struct net_device *dev)
*/
BUG_ON(pppoe_pernet(dev_net(dev)) == NULL);
- write_lock_bh(&pn->hash_lock);
- po = pn->hash_table[i];
+ spin_lock(&pn->hash_lock);
+ po = rcu_dereference_protected(pn->hash_table[i],
+ lockdep_is_held(&pn->hash_lock));
}
}
- write_unlock_bh(&pn->hash_lock);
+ spin_unlock(&pn->hash_lock);
}
static int pppoe_device_event(struct notifier_block *this,
@@ -542,6 +548,7 @@ static int pppoe_create(struct net *net, struct socket *sock, int kern)
return -ENOMEM;
sock_init_data(sock, sk);
+ sock_set_flag(sk, SOCK_RCU_FREE);
sock->state = SS_UNCONNECTED;
sock->ops = &pppoe_ops;
@@ -681,9 +688,9 @@ static int pppoe_connect(struct socket *sock, struct sockaddr *uservaddr,
&sp->sa_addr.pppoe,
sizeof(struct pppoe_addr));
- write_lock_bh(&pn->hash_lock);
+ spin_lock(&pn->hash_lock);
error = __set_item(pn, po);
- write_unlock_bh(&pn->hash_lock);
+ spin_unlock(&pn->hash_lock);
if (error < 0)
goto err_put;
@@ -1052,11 +1059,11 @@ static inline struct pppox_sock *pppoe_get_idx(struct pppoe_net *pn, loff_t pos)
int i;
for (i = 0; i < PPPOE_HASH_SIZE; i++) {
- po = pn->hash_table[i];
+ po = rcu_dereference(pn->hash_table[i]);
while (po) {
if (!pos--)
goto out;
- po = po->next;
+ po = rcu_dereference(po->next);
}
}
@@ -1065,19 +1072,19 @@ static inline struct pppox_sock *pppoe_get_idx(struct pppoe_net *pn, loff_t pos)
}
static void *pppoe_seq_start(struct seq_file *seq, loff_t *pos)
- __acquires(pn->hash_lock)
+ __acquires(RCU)
{
struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
loff_t l = *pos;
- read_lock_bh(&pn->hash_lock);
+ rcu_read_lock();
return l ? pppoe_get_idx(pn, --l) : SEQ_START_TOKEN;
}
static void *pppoe_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
- struct pppox_sock *po;
+ struct pppox_sock *po, *next;
++*pos;
if (v == SEQ_START_TOKEN) {
@@ -1085,14 +1092,15 @@ static void *pppoe_seq_next(struct seq_file *seq, void *v, loff_t *pos)
goto out;
}
po = v;
- if (po->next)
- po = po->next;
+ next = rcu_dereference(po->next);
+ if (next)
+ po = next;
else {
int hash = hash_item(po->pppoe_pa.sid, po->pppoe_pa.remote);
po = NULL;
while (++hash < PPPOE_HASH_SIZE) {
- po = pn->hash_table[hash];
+ po = rcu_dereference(pn->hash_table[hash]);
if (po)
break;
}
@@ -1103,10 +1111,9 @@ static void *pppoe_seq_next(struct seq_file *seq, void *v, loff_t *pos)
}
static void pppoe_seq_stop(struct seq_file *seq, void *v)
- __releases(pn->hash_lock)
+ __releases(RCU)
{
- struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
- read_unlock_bh(&pn->hash_lock);
+ rcu_read_unlock();
}
static const struct seq_operations pppoe_seq_ops = {
@@ -1149,7 +1156,7 @@ static __net_init int pppoe_init_net(struct net *net)
struct pppoe_net *pn = pppoe_pernet(net);
struct proc_dir_entry *pde;
- rwlock_init(&pn->hash_lock);
+ spin_lock_init(&pn->hash_lock);
pde = proc_create_net("pppoe", 0444, net->proc_net,
&pppoe_seq_ops, sizeof(struct seq_net_private));
diff --git a/include/linux/if_pppox.h b/include/linux/if_pppox.h
index ff3beda1312c..db45d6f1c4f4 100644
--- a/include/linux/if_pppox.h
+++ b/include/linux/if_pppox.h
@@ -43,7 +43,7 @@ struct pppox_sock {
/* struct sock must be the first member of pppox_sock */
struct sock sk;
struct ppp_channel chan;
- struct pppox_sock *next; /* for hash table */
+ struct pppox_sock __rcu *next; /* for hash table */
union {
struct pppoe_opt pppoe;
struct pptp_opt pptp;
--
2.43.0
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