sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/include/net/inet_common.h b/include/net/inet_common.h
new file mode 100644
index 000000000..3d747896b
--- /dev/null
+++ b/include/net/inet_common.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _INET_COMMON_H
+#define _INET_COMMON_H
+
+#include <linux/indirect_call_wrapper.h>
+#include <linux/net.h>
+#include <linux/netdev_features.h>
+#include <linux/types.h>
+#include <net/sock.h>
+
+extern const struct proto_ops inet_stream_ops;
+extern const struct proto_ops inet_dgram_ops;
+
+/*
+ *	INET4 prototypes used by INET6
+ */
+
+struct msghdr;
+struct net;
+struct page;
+struct sock;
+struct socket;
+
+int inet_release(struct socket *sock);
+int inet_stream_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
+			int addr_len, int flags);
+int __inet_stream_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
+			  int addr_len, int flags, int is_sendmsg);
+int inet_dgram_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
+		       int addr_len, int flags);
+int inet_accept(struct socket *sock, struct socket *newsock,
+		struct proto_accept_arg *arg);
+void __inet_accept(struct socket *sock, struct socket *newsock,
+		   struct sock *newsk);
+int inet_send_prepare(struct sock *sk);
+int inet_sendmsg(struct socket *sock, struct msghdr *msg, size_t size);
+void inet_splice_eof(struct socket *sock);
+int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
+		 int flags);
+int inet_shutdown(struct socket *sock, int how);
+int inet_listen(struct socket *sock, int backlog);
+int __inet_listen_sk(struct sock *sk, int backlog);
+void inet_sock_destruct(struct sock *sk);
+int inet_bind(struct socket *sock, struct sockaddr_unsized *uaddr, int addr_len);
+int inet_bind_sk(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len);
+/* Don't allocate port at this moment, defer to connect. */
+#define BIND_FORCE_ADDRESS_NO_PORT	(1 << 0)
+/* Grab and release socket lock. */
+#define BIND_WITH_LOCK			(1 << 1)
+/* Called from BPF program. */
+#define BIND_FROM_BPF			(1 << 2)
+/* Skip CAP_NET_BIND_SERVICE check. */
+#define BIND_NO_CAP_NET_BIND_SERVICE	(1 << 3)
+int __inet_bind(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len,
+		u32 flags);
+int inet_getname(struct socket *sock, struct sockaddr *uaddr,
+		 int peer);
+int inet_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
+int inet_ctl_sock_create(struct sock **sk, unsigned short family,
+			 unsigned short type, unsigned char protocol,
+			 struct net *net);
+int inet_recv_error(struct sock *sk, struct msghdr *msg, int len);
+
+struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb);
+int inet_gro_complete(struct sk_buff *skb, int nhoff);
+struct sk_buff *inet_gso_segment(struct sk_buff *skb,
+				 netdev_features_t features);
+
+static inline void inet_ctl_sock_destroy(struct sock *sk)
+{
+	if (sk)
+		sock_release(sk->sk_socket);
+}
+
+#define indirect_call_gro_receive(f2, f1, cb, head, skb)	\
+({								\
+	unlikely(gro_recursion_inc_test(skb)) ?			\
+		NAPI_GRO_CB(skb)->flush |= 1, NULL :		\
+		INDIRECT_CALL_2(cb, f2, f1, head, skb);		\
+})
+
+#endif