[PATCH 5.14 432/849] tcp: switch orphan_count to bare per-cpu counters

From: Greg Kroah-Hartman
Date: Mon Nov 15 2021 - 20:32:11 EST

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 19757cebf0c5016a1f36f7fe9810a9f0b33c0832 ]

Use of percpu_counter structure to track count of orphaned
sockets is causing problems on modern hosts with 256 cpus
or more.

Stefan Bach reported a serious spinlock contention in real workloads,
that I was able to reproduce with a netfilter rule dropping
incoming FIN packets.

53.56% server [kernel.kallsyms] [k] queued_spin_lock_slowpath
|
---queued_spin_lock_slowpath
|
--53.51%--_raw_spin_lock_irqsave
|
--53.51%--__percpu_counter_sum
tcp_check_oom
|
|--39.03%--__tcp_close
| tcp_close
| inet_release
| inet6_release
| sock_close
| __fput
| ____fput
| task_work_run
| exit_to_usermode_loop
| do_syscall_64
| entry_SYSCALL_64_after_hwframe
| __GI___libc_close
|
--14.48%--tcp_out_of_resources
tcp_write_timeout
tcp_retransmit_timer
tcp_write_timer_handler
tcp_write_timer
call_timer_fn
expire_timers
__run_timers
run_timer_softirq
__softirqentry_text_start

As explained in commit cf86a086a180 ("net/dst: use a smaller percpu_counter
batch for dst entries accounting"), default batch size is too big
for the default value of tcp_max_orphans (262144).

But even if we reduce batch sizes, there would still be cases
where the estimated count of orphans is beyond the limit,
and where tcp_too_many_orphans() has to call the expensive
percpu_counter_sum_positive().

One solution is to use plain per-cpu counters, and have
a timer to periodically refresh this cache.

Updating this cache every 100ms seems about right, tcp pressure
state is not radically changing over shorter periods.

percpu_counter was nice 15 years ago while hosts had less
than 16 cpus, not anymore by current standards.

v2: Fix the build issue for CONFIG_CRYPTO_DEV_CHELSIO_TLS=m,
reported by kernel test robot <lkp@xxxxxxxxx>
Remove unused socket argument from tcp_too_many_orphans()

Fixes: dd24c00191d5 ("net: Use a percpu_counter for orphan_count")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Stefan Bach <sfb@xxxxxxxxxx>
Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
.../chelsio/inline_crypto/chtls/chtls_cm.c | 2 +-
.../chelsio/inline_crypto/chtls/chtls_cm.h | 2 +-
include/net/inet_connection_sock.h | 2 +-
include/net/sock.h | 2 +-
include/net/tcp.h | 17 ++-------
net/dccp/dccp.h | 2 +-
net/dccp/proto.c | 14 ++-----
net/ipv4/inet_connection_sock.c | 4 +-
net/ipv4/inet_hashtables.c | 2 +-
net/ipv4/proc.c | 2 +-
net/ipv4/tcp.c | 38 ++++++++++++++++---
11 files changed, 49 insertions(+), 38 deletions(-)

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 bcad69c480740..4af5561cbfc54 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
@@ -870,7 +870,7 @@ static void do_abort_syn_rcv(struct sock *child, struct sock *parent)
* created only after 3 way handshake is done.
*/
sock_orphan(child);
- percpu_counter_inc((child)->sk_prot->orphan_count);
+ INC_ORPHAN_COUNT(child);
chtls_release_resources(child);
chtls_conn_done(child);
} else {
diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
index b1161bdeda4dc..f61ca657601ca 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
@@ -95,7 +95,7 @@ struct deferred_skb_cb {
#define WSCALE_OK(tp) ((tp)->rx_opt.wscale_ok)
#define TSTAMP_OK(tp) ((tp)->rx_opt.tstamp_ok)
#define SACK_OK(tp) ((tp)->rx_opt.sack_ok)
-#define INC_ORPHAN_COUNT(sk) percpu_counter_inc((sk)->sk_prot->orphan_count)
+#define INC_ORPHAN_COUNT(sk) this_cpu_inc(*(sk)->sk_prot->orphan_count)

/* TLS SKB */
#define skb_ulp_tls_inline(skb) (ULP_SKB_CB(skb)->ulp.tls.ofld)
diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index b06c2d02ec84e..fa6a87246a7b8 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -289,7 +289,7 @@ static inline void inet_csk_prepare_for_destroy_sock(struct sock *sk)
{
/* The below has to be done to allow calling inet_csk_destroy_sock */
sock_set_flag(sk, SOCK_DEAD);
- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(*sk->sk_prot->orphan_count);
}

void inet_csk_destroy_sock(struct sock *sk);
diff --git a/include/net/sock.h b/include/net/sock.h
index d28b9bb5ef5a0..95e0a290b648b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1235,7 +1235,7 @@ struct proto {
unsigned int useroffset; /* Usercopy region offset */
unsigned int usersize; /* Usercopy region size */

- struct percpu_counter *orphan_count;
+ unsigned int __percpu *orphan_count;

struct request_sock_ops *rsk_prot;
struct timewait_sock_ops *twsk_prot;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 784d5c3ef1c5b..c5cf900539209 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -48,7 +48,9 @@

extern struct inet_hashinfo tcp_hashinfo;

-extern struct percpu_counter tcp_orphan_count;
+DECLARE_PER_CPU(unsigned int, tcp_orphan_count);
+int tcp_orphan_count_sum(void);
+
void tcp_time_wait(struct sock *sk, int state, int timeo);

#define MAX_TCP_HEADER L1_CACHE_ALIGN(128 + MAX_HEADER)
@@ -290,19 +292,6 @@ static inline bool tcp_out_of_memory(struct sock *sk)

void sk_forced_mem_schedule(struct sock *sk, int size);

-static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
-{
- struct percpu_counter *ocp = sk->sk_prot->orphan_count;
- int orphans = percpu_counter_read_positive(ocp);
-
- if (orphans << shift > sysctl_tcp_max_orphans) {
- orphans = percpu_counter_sum_positive(ocp);
- if (orphans << shift > sysctl_tcp_max_orphans)
- return true;
- }
- return false;
-}
-
bool tcp_check_oom(struct sock *sk, int shift);


diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index c5c1d2b8045e8..5183e627468d8 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -48,7 +48,7 @@ extern bool dccp_debug;

extern struct inet_hashinfo dccp_hashinfo;

-extern struct percpu_counter dccp_orphan_count;
+DECLARE_PER_CPU(unsigned int, dccp_orphan_count);

void dccp_time_wait(struct sock *sk, int state, int timeo);

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 7eb0fb2319407..40e9c61bd14c2 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -42,8 +42,8 @@ DEFINE_SNMP_STAT(struct dccp_mib, dccp_statistics) __read_mostly;

EXPORT_SYMBOL_GPL(dccp_statistics);

-struct percpu_counter dccp_orphan_count;
-EXPORT_SYMBOL_GPL(dccp_orphan_count);
+DEFINE_PER_CPU(unsigned int, dccp_orphan_count);
+EXPORT_PER_CPU_SYMBOL_GPL(dccp_orphan_count);

struct inet_hashinfo dccp_hashinfo;
EXPORT_SYMBOL_GPL(dccp_hashinfo);
@@ -1055,7 +1055,7 @@ adjudge_to_death:
bh_lock_sock(sk);
WARN_ON(sock_owned_by_user(sk));

- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(dccp_orphan_count);

/* Have we already been destroyed by a softirq or backlog? */
if (state != DCCP_CLOSED && sk->sk_state == DCCP_CLOSED)
@@ -1115,13 +1115,10 @@ static int __init dccp_init(void)

BUILD_BUG_ON(sizeof(struct dccp_skb_cb) >
sizeof_field(struct sk_buff, cb));
- rc = percpu_counter_init(&dccp_orphan_count, 0, GFP_KERNEL);
- if (rc)
- goto out_fail;
inet_hashinfo_init(&dccp_hashinfo);
rc = inet_hashinfo2_init_mod(&dccp_hashinfo);
if (rc)
- goto out_free_percpu;
+ goto out_fail;
rc = -ENOBUFS;
dccp_hashinfo.bind_bucket_cachep =
kmem_cache_create("dccp_bind_bucket",
@@ -1226,8 +1223,6 @@ out_free_bind_bucket_cachep:
kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
out_free_hashinfo2:
inet_hashinfo2_free_mod(&dccp_hashinfo);
-out_free_percpu:
- percpu_counter_destroy(&dccp_orphan_count);
out_fail:
dccp_hashinfo.bhash = NULL;
dccp_hashinfo.ehash = NULL;
@@ -1250,7 +1245,6 @@ static void __exit dccp_fini(void)
dccp_ackvec_exit();
dccp_sysctl_exit();
inet_hashinfo2_free_mod(&dccp_hashinfo);
- percpu_counter_destroy(&dccp_orphan_count);
}

module_init(dccp_init);
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 754013fa393bb..e0f9ff4807bbb 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -1014,7 +1014,7 @@ void inet_csk_destroy_sock(struct sock *sk)

sk_refcnt_debug_release(sk);

- percpu_counter_dec(sk->sk_prot->orphan_count);
+ this_cpu_dec(*sk->sk_prot->orphan_count);

sock_put(sk);
}
@@ -1073,7 +1073,7 @@ static void inet_child_forget(struct sock *sk, struct request_sock *req,

sock_orphan(child);

- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(*sk->sk_prot->orphan_count);

if (sk->sk_protocol == IPPROTO_TCP && tcp_rsk(req)->tfo_listener) {
BUG_ON(rcu_access_pointer(tcp_sk(child)->fastopen_rsk) != req);
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index bfb522e513461..75737267746f8 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -598,7 +598,7 @@ bool inet_ehash_nolisten(struct sock *sk, struct sock *osk, bool *found_dup_sk)
if (ok) {
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
} else {
- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(*sk->sk_prot->orphan_count);
inet_sk_set_state(sk, TCP_CLOSE);
sock_set_flag(sk, SOCK_DEAD);
inet_csk_destroy_sock(sk);
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index b0d3a09dc84e7..f30273afb5399 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -53,7 +53,7 @@ static int sockstat_seq_show(struct seq_file *seq, void *v)
struct net *net = seq->private;
int orphans, sockets;

- orphans = percpu_counter_sum_positive(&tcp_orphan_count);
+ orphans = tcp_orphan_count_sum();
sockets = proto_sockets_allocated_sum_positive(&tcp_prot);

socket_seq_show(seq);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 8cb44040ec68b..9c38c22c92fbb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -287,8 +287,8 @@ enum {
TCP_CMSG_TS = 2
};

-struct percpu_counter tcp_orphan_count;
-EXPORT_SYMBOL_GPL(tcp_orphan_count);
+DEFINE_PER_CPU(unsigned int, tcp_orphan_count);
+EXPORT_PER_CPU_SYMBOL_GPL(tcp_orphan_count);

long sysctl_tcp_mem[3] __read_mostly;
EXPORT_SYMBOL(sysctl_tcp_mem);
@@ -2690,11 +2690,36 @@ void tcp_shutdown(struct sock *sk, int how)
}
EXPORT_SYMBOL(tcp_shutdown);

+int tcp_orphan_count_sum(void)
+{
+ int i, total = 0;
+
+ for_each_possible_cpu(i)
+ total += per_cpu(tcp_orphan_count, i);
+
+ return max(total, 0);
+}
+
+static int tcp_orphan_cache;
+static struct timer_list tcp_orphan_timer;
+#define TCP_ORPHAN_TIMER_PERIOD msecs_to_jiffies(100)
+
+static void tcp_orphan_update(struct timer_list *unused)
+{
+ WRITE_ONCE(tcp_orphan_cache, tcp_orphan_count_sum());
+ mod_timer(&tcp_orphan_timer, jiffies + TCP_ORPHAN_TIMER_PERIOD);
+}
+
+static bool tcp_too_many_orphans(int shift)
+{
+ return READ_ONCE(tcp_orphan_cache) << shift > sysctl_tcp_max_orphans;
+}
+
bool tcp_check_oom(struct sock *sk, int shift)
{
bool too_many_orphans, out_of_socket_memory;

- too_many_orphans = tcp_too_many_orphans(sk, shift);
+ too_many_orphans = tcp_too_many_orphans(shift);
out_of_socket_memory = tcp_out_of_memory(sk);

if (too_many_orphans)
@@ -2803,7 +2828,7 @@ adjudge_to_death:
/* remove backlog if any, without releasing ownership. */
__release_sock(sk);

- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(tcp_orphan_count);

/* Have we already been destroyed by a softirq or backlog? */
if (state != TCP_CLOSE && sk->sk_state == TCP_CLOSE)
@@ -4504,7 +4529,10 @@ void __init tcp_init(void)
sizeof_field(struct sk_buff, cb));

percpu_counter_init(&tcp_sockets_allocated, 0, GFP_KERNEL);
- percpu_counter_init(&tcp_orphan_count, 0, GFP_KERNEL);
+
+ timer_setup(&tcp_orphan_timer, tcp_orphan_update, TIMER_DEFERRABLE);
+ mod_timer(&tcp_orphan_timer, jiffies + TCP_ORPHAN_TIMER_PERIOD);
+
inet_hashinfo_init(&tcp_hashinfo);
inet_hashinfo2_init(&tcp_hashinfo, "tcp_listen_portaddr_hash",
thash_entries, 21, /* one slot per 2 MB*/
--
2.33.0