[PATCH 5.19 0367/1157] ping: convert to RCU lookups, get rid of rwlock

Greg Kroah-Hartman
2022-08-15T23:35:00Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit dbca1596bbb08318f5e3b3b99f8ca0a0d3830a65 ]

Using rwlock in networking code is extremely risky.
writers can starve if enough readers are constantly
grabing the rwlock.

I thought rwlock were at fault and sent this patch:

https://lkml.org/lkml/2022/6/17/272

But Peter and Linus essentially told me rwlock had to be unfair.

We need to get rid of rwlock in networking code.

Fixes: c319b4d76b9e ("net: ipv4: add IPPROTO_ICMP socket kind")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/ping.c | 36 ++++++++++++++++--------------------
1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 3c6101def7d6..b83c2bd9d722 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -50,7 +50,7 @@

struct ping_table {
struct hlist_nulls_head hash[PING_HTABLE_SIZE];
- rwlock_t lock;
+ spinlock_t lock;
};

static struct ping_table ping_table;
@@ -82,7 +82,7 @@ int ping_get_port(struct sock *sk, unsigned short ident)
struct sock *sk2 = NULL;

isk = inet_sk(sk);
- write_lock_bh(&ping_table.lock);
+ spin_lock(&ping_table.lock);
if (ident == 0) {
u32 i;
u16 result = ping_port_rover + 1;
@@ -128,14 +128,15 @@ int ping_get_port(struct sock *sk, unsigned short ident)
if (sk_unhashed(sk)) {
pr_debug("was not hashed\n");
sock_hold(sk);
- hlist_nulls_add_head(&sk->sk_nulls_node, hlist);
+ sock_set_flag(sk, SOCK_RCU_FREE);
+ hlist_nulls_add_head_rcu(&sk->sk_nulls_node, hlist);
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
}
- write_unlock_bh(&ping_table.lock);
+ spin_unlock(&ping_table.lock);
return 0;

fail:
- write_unlock_bh(&ping_table.lock);
+ spin_unlock(&ping_table.lock);
return 1;
}
EXPORT_SYMBOL_GPL(ping_get_port);
@@ -153,19 +154,19 @@ void ping_unhash(struct sock *sk)
struct inet_sock *isk = inet_sk(sk);

pr_debug("ping_unhash(isk=%p,isk->num=%u)\n", isk, isk->inet_num);
- write_lock_bh(&ping_table.lock);
+ spin_lock(&ping_table.lock);
if (sk_hashed(sk)) {
- hlist_nulls_del(&sk->sk_nulls_node);
- sk_nulls_node_init(&sk->sk_nulls_node);
+ hlist_nulls_del_init_rcu(&sk->sk_nulls_node);
sock_put(sk);
isk->inet_num = 0;
isk->inet_sport = 0;
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
}
- write_unlock_bh(&ping_table.lock);
+ spin_unlock(&ping_table.lock);
}
EXPORT_SYMBOL_GPL(ping_unhash);

+/* Called under rcu_read_lock() */
static struct sock *ping_lookup(struct net *net, struct sk_buff *skb, u16 ident)
{
struct hlist_nulls_head *hslot = ping_hashslot(&ping_table, net, ident);
@@ -190,8 +191,6 @@ static struct sock *ping_lookup(struct net *net, struct sk_buff *skb, u16 ident)
return NULL;
}

- read_lock_bh(&ping_table.lock);
-
ping_portaddr_for_each_entry(sk, hnode, hslot) {
isk = inet_sk(sk);

@@ -230,13 +229,11 @@ static struct sock *ping_lookup(struct net *net, struct sk_buff *skb, u16 ident)
sk->sk_bound_dev_if != sdif)
continue;

- sock_hold(sk);
goto exit;
}

sk = NULL;
exit:
- read_unlock_bh(&ping_table.lock);

return sk;
}
@@ -592,7 +589,7 @@ void ping_err(struct sk_buff *skb, int offset, u32 info)
sk->sk_err = err;
sk_error_report(sk);
out:
- sock_put(sk);
+ return;
}
EXPORT_SYMBOL_GPL(ping_err);

@@ -998,7 +995,6 @@ enum skb_drop_reason ping_rcv(struct sk_buff *skb)
reason = __ping_queue_rcv_skb(sk, skb2);
else
reason = SKB_DROP_REASON_NOMEM;
- sock_put(sk);
}

if (reason)
@@ -1084,13 +1080,13 @@ static struct sock *ping_get_idx(struct seq_file *seq, loff_t pos)
}

void *ping_seq_start(struct seq_file *seq, loff_t *pos, sa_family_t family)
- __acquires(ping_table.lock)
+ __acquires(RCU)
{
struct ping_iter_state *state = seq->private;
state->bucket = 0;
state->family = family;

- read_lock_bh(&ping_table.lock);
+ rcu_read_lock();

return *pos ? ping_get_idx(seq, *pos-1) : SEQ_START_TOKEN;
}
@@ -1116,9 +1112,9 @@ void *ping_seq_next(struct seq_file *seq, void *v, loff_t *pos)
EXPORT_SYMBOL_GPL(ping_seq_next);

void ping_seq_stop(struct seq_file *seq, void *v)
- __releases(ping_table.lock)
+ __releases(RCU)
{
- read_unlock_bh(&ping_table.lock);
+ rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(ping_seq_stop);

@@ -1202,5 +1198,5 @@ void __init ping_init(void)

for (i = 0; i < PING_HTABLE_SIZE; i++)
INIT_HLIST_NULLS_HEAD(&ping_table.hash[i], i);
- rwlock_init(&ping_table.lock);
+ spin_lock_init(&ping_table.lock);
}
--
2.35.1