Merge branch 'bpf-allow-opt-out-from-sk-sk_prot-memory_allocated'

Kuniyuki Iwashima says:

====================
bpf: Allow opt-out from sk->sk_prot->memory_allocated.

This series allows opting out of the global per-protocol memory
accounting if socket is configured as such by sysctl or BPF prog.

This series is the successor of the series below [0], but the changes
now fall in net and bpf subsystems only.

I discussed with Roman Gushchin offlist, and he suggested not mixing
two independent subsystems and it would be cleaner not to depend on
memcg.

So, sk->sk_memcg and memcg code are no longer touched, and instead we
use another hole near sk->sk_prot to store a flag for the pure net
opt-out feature.

Overview of the series:

  patch 1 is misc cleanup
  patch 2 allows opt-out from sk->sk_prot->memory_allocated
  patch 3 introduces net.core.bypass_prot_mem
  patch 4 & 5 supports flagging sk->sk_bypass_prot_mem via bpf_setsockopt()
  patch 6 is selftest

Thank you very much for all your help, Shakeel, Roman, Martin, and Eric!

[0]: https://lore.kernel.org/bpf/20250920000751.2091731-1-kuniyu@google.com/

Changes:
  v2:
    * Patch 2:
      * Fill kdoc for skc_bypass_prot_mem
    * Patch 6
      * Fix server fd leak in tcp_create_sockets()
      * Avoid close(0) in check_bypass()

  v1: https://lore.kernel.org/bpf/20251007001120.2661442-1-kuniyu@google.com/
====================

Link: https://patch.msgid.link/20251014235604.3057003-1-kuniyu@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

5 files changed, 12 insertions, 0 deletions

diff --git a/include/net/netns/core.h b/include/net/netns/core.h
index cb9c3e4cd738..9ef3d70e5e9c 100644
--- a/include/net/netns/core.h
+++ b/include/net/netns/core.h
@@ -17,6 +17,7 @@ struct netns_core {
 	int	sysctl_optmem_max;
 	u8	sysctl_txrehash;
 	u8	sysctl_tstamp_allow_data;
+	u8	sysctl_bypass_prot_mem;
 
 #ifdef CONFIG_PROC_FS
 	struct prot_inuse __percpu *prot_inuse;
diff --git a/include/net/proto_memory.h b/include/net/proto_memory.h
index 8e91a8fa31b5..ad6d703ce6fe 100644
--- a/include/net/proto_memory.h
+++ b/include/net/proto_memory.h
@@ -35,6 +35,9 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
 	    mem_cgroup_sk_under_memory_pressure(sk))
 		return true;
 
+	if (sk->sk_bypass_prot_mem)
+		return false;
+
 	return !!READ_ONCE(*sk->sk_prot->memory_pressure);
 }
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 30ac2eb4ef9b..415e7381aa50 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -118,6 +118,7 @@ typedef __u64 __bitwise __addrpair;
  *	@skc_reuseport: %SO_REUSEPORT setting
  *	@skc_ipv6only: socket is IPV6 only
  *	@skc_net_refcnt: socket is using net ref counting
+ *	@skc_bypass_prot_mem: bypass the per-protocol memory accounting for skb
  *	@skc_bound_dev_if: bound device index if != 0
  *	@skc_bind_node: bind hash linkage for various protocol lookup tables
  *	@skc_portaddr_node: second hash linkage for UDP/UDP-Lite protocol
@@ -174,6 +175,7 @@ struct sock_common {
 	unsigned char		skc_reuseport:1;
 	unsigned char		skc_ipv6only:1;
 	unsigned char		skc_net_refcnt:1;
+	unsigned char		skc_bypass_prot_mem:1;
 	int			skc_bound_dev_if;
 	union {
 		struct hlist_node	skc_bind_node;
@@ -381,6 +383,7 @@ struct sock {
 #define sk_reuseport		__sk_common.skc_reuseport
 #define sk_ipv6only		__sk_common.skc_ipv6only
 #define sk_net_refcnt		__sk_common.skc_net_refcnt
+#define sk_bypass_prot_mem	__sk_common.skc_bypass_prot_mem
 #define sk_bound_dev_if		__sk_common.skc_bound_dev_if
 #define sk_bind_node		__sk_common.skc_bind_node
 #define sk_prot			__sk_common.skc_prot
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 1e547138f4fb..439e327fdbfa 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -303,6 +303,9 @@ static inline bool tcp_under_memory_pressure(const struct sock *sk)
 	    mem_cgroup_sk_under_memory_pressure(sk))
 		return true;
 
+	if (sk->sk_bypass_prot_mem)
+		return false;
+
 	return READ_ONCE(tcp_memory_pressure);
 }
 /*
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6829936d33f5..6eb75ad900b1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7200,6 +7200,8 @@ enum {
 	TCP_BPF_SYN_MAC         = 1007, /* Copy the MAC, IP[46], and TCP header */
 	TCP_BPF_SOCK_OPS_CB_FLAGS = 1008, /* Get or Set TCP sock ops flags */
 	SK_BPF_CB_FLAGS		= 1009, /* Get or set sock ops flags in socket */
+	SK_BPF_BYPASS_PROT_MEM	= 1010, /* Get or Set sk->sk_bypass_prot_mem */
+
 };
 
 enum {