bpf, net: Rework cookie generator as per-cpu one

With its use in BPF, the cookie generator can be called very frequently
in particular when used out of cgroup v2 hooks (e.g. connect / sendmsg)
and attached to the root cgroup, for example, when used in v1/v2 mixed
environments. In particular, when there's a high churn on sockets in the
system there can be many parallel requests to the bpf_get_socket_cookie()
and bpf_get_netns_cookie() helpers which then cause contention on the
atomic counter.

As similarly done in f991bd2e1421 ("fs: introduce a per-cpu last_ino
allocator"), add a small helper library that both can use for the 64 bit
counters. Given this can be called from different contexts, we also need
to deal with potential nested calls even though in practice they are
considered extremely rare. One idea as suggested by Eric Dumazet was
to use a reverse counter for this situation since we don't expect 64 bit
overflows anyways; that way, we can avoid bigger gaps in the 64 bit
counter space compared to just batch-wise increase. Even on machines
with small number of cores (e.g. 4) the cookie generation shrinks from
min/max/med/avg (ns) of 22/50/40/38.9 down to 10/35/14/17.3 when run
in parallel from multiple CPUs.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Link: https://lore.kernel.org/bpf/8a80b8d27d3c49f9a14e1d5213c19d8be87d1dc8.1601477936.git.daniel@iogearbox.net

diff --git a/include/linux/cookie.h b/include/linux/cookie.h
new file mode 100644 (file)
index 0000000..0c159f5
--- /dev/null
+++ b/include/linux/cookie.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_COOKIE_H
+#define __LINUX_COOKIE_H
+
+#include <linux/atomic.h>
+#include <linux/percpu.h>
+#include <asm/local.h>
+
+struct pcpu_gen_cookie {
+       local_t nesting;
+       u64 last;
+} __aligned(16);
+
+struct gen_cookie {
+       struct pcpu_gen_cookie __percpu *local;
+       atomic64_t forward_last ____cacheline_aligned_in_smp;
+       atomic64_t reverse_last;
+};
+
+#define COOKIE_LOCAL_BATCH     4096
+
+#define DEFINE_COOKIE(name)                                            \
+       static DEFINE_PER_CPU(struct pcpu_gen_cookie, __##name);        \
+       static struct gen_cookie name = {                               \
+               .local          = &__##name,                            \
+               .forward_last   = ATOMIC64_INIT(0),                     \
+               .reverse_last   = ATOMIC64_INIT(0),                     \
+       }
+
+static __always_inline u64 gen_cookie_next(struct gen_cookie *gc)
+{
+       struct pcpu_gen_cookie *local = this_cpu_ptr(gc->local);
+       u64 val;
+
+       if (likely(local_inc_return(&local->nesting) == 1)) {
+               val = local->last;
+               if (__is_defined(CONFIG_SMP) &&
+                   unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0)) {
+                       s64 next = atomic64_add_return(COOKIE_LOCAL_BATCH,
+                                                      &gc->forward_last);
+                       val = next - COOKIE_LOCAL_BATCH;
+               }
+               local->last = ++val;
+       } else {
+               val = atomic64_dec_return(&gc->reverse_last);
+       }
+       local_dec(&local->nesting);
+       return val;
+}
+
+#endif /* __LINUX_COOKIE_H */

diff --git a/include/linux/sock_diag.h b/include/linux/sock_diag.h
index 15fe980a27ead226cdf5cbd00df3c54f2dd944a6..0b9ecd8cf9793bc26138a0a36474e78773fb4f31 100644 (file)
--- a/include/linux/sock_diag.h
+++ b/include/linux/sock_diag.h
@@ -25,7 +25,19 @@ void sock_diag_unregister(const struct sock_diag_handler *h);
 void sock_diag_register_inet_compat(int (*fn)(struct sk_buff *skb, struct nlmsghdr *nlh));
 void sock_diag_unregister_inet_compat(int (*fn)(struct sk_buff *skb, struct nlmsghdr *nlh));
 
-u64 sock_gen_cookie(struct sock *sk);
+u64 __sock_gen_cookie(struct sock *sk);
+
+static inline u64 sock_gen_cookie(struct sock *sk)
+{
+       u64 cookie;
+
+       preempt_disable();
+       cookie = __sock_gen_cookie(sk);
+       preempt_enable();
+
+       return cookie;
+}
+
 int sock_diag_check_cookie(struct sock *sk, const __u32 *cookie);
 void sock_diag_save_cookie(struct sock *sk, __u32 *cookie);
 

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 2ee5901bec7a6758c4c0cf601ca03fc453508d09..22bc07f4b043d4a577d1ac568d84600a45e0e2d4 100644 (file)
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -230,7 +230,7 @@ extern struct list_head net_namespace_list;
 struct net *get_net_ns_by_pid(pid_t pid);
 struct net *get_net_ns_by_fd(int fd);
 
-u64 net_gen_cookie(struct net *net);
+u64 __net_gen_cookie(struct net *net);
 
 #ifdef CONFIG_SYSCTL
 void ipx_register_sysctl(void);

diff --git a/kernel/bpf/reuseport_array.c b/kernel/bpf/reuseport_array.c
index 5a2ba11824938b028f57afb988404d3ed3f97deb..a55cd542f2ced4bd931bfbb4720473700d28b869 100644 (file)
--- a/kernel/bpf/reuseport_array.c
+++ b/kernel/bpf/reuseport_array.c
@@ -191,7 +191,7 @@ int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
        rcu_read_lock();
        sk = reuseport_array_lookup_elem(map, key);
        if (sk) {
-               *(u64 *)value = sock_gen_cookie(sk);
+               *(u64 *)value = __sock_gen_cookie(sk);
                err = 0;
        } else {
                err = -ENOENT;

diff --git a/net/core/filter.c b/net/core/filter.c
index fa01c697977dbf016ef375c8fb8f26d0ef21e45a..a0776e48dcc95378f1f5186c2796f6b7605932e2 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4232,7 +4232,7 @@ const struct bpf_func_proto bpf_xdp_output_proto = {
 
 BPF_CALL_1(bpf_get_socket_cookie, struct sk_buff *, skb)
 {
-       return skb->sk ? sock_gen_cookie(skb->sk) : 0;
+       return skb->sk ? __sock_gen_cookie(skb->sk) : 0;
 }
 
 static const struct bpf_func_proto bpf_get_socket_cookie_proto = {
@@ -4244,7 +4244,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_proto = {
 
 BPF_CALL_1(bpf_get_socket_cookie_sock_addr, struct bpf_sock_addr_kern *, ctx)
 {
-       return sock_gen_cookie(ctx->sk);
+       return __sock_gen_cookie(ctx->sk);
 }
 
 static const struct bpf_func_proto bpf_get_socket_cookie_sock_addr_proto = {
@@ -4256,7 +4256,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_sock_addr_proto = {
 
 BPF_CALL_1(bpf_get_socket_cookie_sock, struct sock *, ctx)
 {
-       return sock_gen_cookie(ctx);
+       return __sock_gen_cookie(ctx);
 }
 
 static const struct bpf_func_proto bpf_get_socket_cookie_sock_proto = {
@@ -4268,7 +4268,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_sock_proto = {
 
 BPF_CALL_1(bpf_get_socket_cookie_sock_ops, struct bpf_sock_ops_kern *, ctx)
 {
-       return sock_gen_cookie(ctx->sk);
+       return __sock_gen_cookie(ctx->sk);
 }
 
 static const struct bpf_func_proto bpf_get_socket_cookie_sock_ops_proto = {
@@ -4281,7 +4281,7 @@ static const struct bpf_func_proto bpf_get_socket_cookie_sock_ops_proto = {
 static u64 __bpf_get_netns_cookie(struct sock *sk)
 {
 #ifdef CONFIG_NET_NS
-       return net_gen_cookie(sk ? sk->sk_net.net : &init_net);
+       return __net_gen_cookie(sk ? sk->sk_net.net : &init_net);
 #else
        return 0;
 #endif

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 944ab214e5ae85acff024d62e03a21fb952207e9..dbc66b896287a49df15e3ca76eb9b6db27c73153 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -19,6 +19,7 @@
 #include <linux/net_namespace.h>
 #include <linux/sched/task.h>
 #include <linux/uidgid.h>
+#include <linux/cookie.h>
 
 #include <net/sock.h>
 #include <net/netlink.h>
@@ -69,16 +70,16 @@ EXPORT_SYMBOL_GPL(pernet_ops_rwsem);
 
 static unsigned int max_gen_ptrs = INITIAL_NET_GEN_PTRS;
 
-static atomic64_t cookie_gen;
+DEFINE_COOKIE(net_cookie);
 
-u64 net_gen_cookie(struct net *net)
+u64 __net_gen_cookie(struct net *net)
 {
        while (1) {
                u64 res = atomic64_read(&net->net_cookie);
 
                if (res)
                        return res;
-               res = atomic64_inc_return(&cookie_gen);
+               res = gen_cookie_next(&net_cookie);
                atomic64_cmpxchg(&net->net_cookie, 0, res);
        }
 }
@@ -1101,7 +1102,10 @@ static int __init net_ns_init(void)
                panic("Could not allocate generic netns");
 
        rcu_assign_pointer(init_net.gen, ng);
-       net_gen_cookie(&init_net);
+
+       preempt_disable();
+       __net_gen_cookie(&init_net);
+       preempt_enable();
 
        down_write(&pernet_ops_rwsem);
        if (setup_net(&init_net, &init_user_ns))

diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
index c13ffbd33d8d6ad4f591571325aaee321df5b242..c9c45b935f9900ddc05d3604e893c0b3c6386206 100644 (file)
--- a/net/core/sock_diag.c
+++ b/net/core/sock_diag.c
@@ -11,7 +11,7 @@
 #include <linux/tcp.h>
 #include <linux/workqueue.h>
 #include <linux/nospec.h>
-
+#include <linux/cookie.h>
 #include <linux/inet_diag.h>
 #include <linux/sock_diag.h>
 
@@ -19,16 +19,17 @@ static const struct sock_diag_handler *sock_diag_handlers[AF_MAX];
 static int (*inet_rcv_compat)(struct sk_buff *skb, struct nlmsghdr *nlh);
 static DEFINE_MUTEX(sock_diag_table_mutex);
 static struct workqueue_struct *broadcast_wq;
-static atomic64_t cookie_gen;
 
-u64 sock_gen_cookie(struct sock *sk)
+DEFINE_COOKIE(sock_cookie);
+
+u64 __sock_gen_cookie(struct sock *sk)
 {
        while (1) {
                u64 res = atomic64_read(&sk->sk_cookie);
 
                if (res)
                        return res;
-               res = atomic64_inc_return(&cookie_gen);
+               res = gen_cookie_next(&sock_cookie);
                atomic64_cmpxchg(&sk->sk_cookie, 0, res);
        }
 }

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 08bc86f51593c285ee260d2786048a633491cce3..e83a80e8f13bf8056ed059e3d973735bc7ee84e0 100644 (file)
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -401,7 +401,7 @@ static void *sock_map_lookup_sys(struct bpf_map *map, void *key)
        if (!sk)
                return ERR_PTR(-ENOENT);
 
-       sock_gen_cookie(sk);
+       __sock_gen_cookie(sk);
        return &sk->sk_cookie;
 }
 
@@ -1209,7 +1209,7 @@ static void *sock_hash_lookup_sys(struct bpf_map *map, void *key)
        if (!sk)
                return ERR_PTR(-ENOENT);
 
-       sock_gen_cookie(sk);
+       __sock_gen_cookie(sk);
        return &sk->sk_cookie;
 }