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, 114 insertions, 0 deletions

diff --git a/include/net/llc_conn.h b/include/net/llc_conn.h
new file mode 100644
index 000000000..e1a302696
--- /dev/null
+++ b/include/net/llc_conn.h
@@ -0,0 +1,114 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LLC_CONN_H
+#define LLC_CONN_H
+/*
+ * Copyright (c) 1997 by Procom Technology, Inc.
+ * 		 2001, 2002 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#include <linux/timer.h>
+#include <net/llc_if.h>
+#include <net/sock.h>
+#include <linux/llc.h>
+
+#define LLC_EVENT                1
+#define LLC_PACKET               2
+
+#define LLC2_P_TIME               2
+#define LLC2_ACK_TIME             1
+#define LLC2_REJ_TIME             3
+#define LLC2_BUSY_TIME            3
+
+struct llc_timer {
+	struct timer_list timer;
+	unsigned long	  expire;	/* timer expire time */
+};
+
+struct llc_sock {
+	/* struct sock must be the first member of llc_sock */
+	struct sock	    sk;
+	struct sockaddr_llc addr;		/* address sock is bound to */
+	u8		    state;		/* state of connection */
+	struct llc_sap	    *sap;		/* pointer to parent SAP */
+	struct llc_addr	    laddr;		/* lsap/mac pair */
+	struct llc_addr	    daddr;		/* dsap/mac pair */
+	struct net_device   *dev;		/* device to send to remote */
+	netdevice_tracker   dev_tracker;
+	u32		    copied_seq;		/* head of yet unread data */
+	u8		    retry_count;	/* number of retries */
+	u8		    ack_must_be_send;
+	u8		    first_pdu_Ns;
+	u8		    npta;
+	struct llc_timer    ack_timer;
+	struct llc_timer    pf_cycle_timer;
+	struct llc_timer    rej_sent_timer;
+	struct llc_timer    busy_state_timer;	/* ind busy clr at remote LLC */
+	u8		    vS;			/* seq# next in-seq I-PDU tx'd*/
+	u8		    vR;			/* seq# next in-seq I-PDU rx'd*/
+	u32		    n2;			/* max nbr re-tx's for timeout*/
+	u32		    n1;			/* max nbr octets in I PDU */
+	u8		    k;			/* tx window size; max = 127 */
+	u8		    rw;			/* rx window size; max = 127 */
+	u8		    p_flag;		/* state flags */
+	u8		    f_flag;
+	u8		    s_flag;
+	u8		    data_flag;
+	u8		    remote_busy_flag;
+	u8		    cause_flag;
+	struct sk_buff_head pdu_unack_q;	/* PUDs sent/waiting ack */
+	u16		    link;		/* network layer link number */
+	u8		    X;			/* a temporary variable */
+	u8		    ack_pf;		/* this flag indicates what is
+						   the P-bit of acknowledge */
+	u8		    failed_data_req; /* recognize that already exist a
+						failed llc_data_req_handler
+						(tx_buffer_full or unacceptable
+						state */
+	u8		    dec_step;
+	u8		    inc_cntr;
+	u8		    dec_cntr;
+	u8		    connect_step;
+	u8		    last_nr;	   /* NR of last pdu received */
+	u32		    rx_pdu_hdr;	   /* used for saving header of last pdu
+					      received and caused sending FRMR.
+					      Used for resending FRMR */
+	u32		    cmsg_flags;
+	struct hlist_node   dev_hash_node;
+};
+
+static inline struct llc_sock *llc_sk(const struct sock *sk)
+{
+	return (struct llc_sock *)sk;
+}
+
+static __inline__ void llc_set_backlog_type(struct sk_buff *skb, char type)
+{
+	skb->cb[sizeof(skb->cb) - 1] = type;
+}
+
+static __inline__ char llc_backlog_type(struct sk_buff *skb)
+{
+	return skb->cb[sizeof(skb->cb) - 1];
+}
+
+struct sock *llc_sk_alloc(struct net *net, int family, gfp_t priority,
+			  struct proto *prot, int kern);
+void llc_sk_stop_all_timers(struct sock *sk, bool sync);
+void llc_sk_free(struct sock *sk);
+
+void llc_sk_reset(struct sock *sk);
+
+/* Access to a connection */
+int llc_conn_state_process(struct sock *sk, struct sk_buff *skb);
+void llc_conn_send_pdu(struct sock *sk, struct sk_buff *skb);
+void llc_conn_rtn_pdu(struct sock *sk, struct sk_buff *skb);
+void llc_conn_resend_i_pdu_as_cmd(struct sock *sk, u8 nr, u8 first_p_bit);
+void llc_conn_resend_i_pdu_as_rsp(struct sock *sk, u8 nr, u8 first_f_bit);
+int llc_conn_remove_acked_pdus(struct sock *conn, u8 nr, u16 *how_many_unacked);
+struct sock *llc_lookup_established(struct llc_sap *sap, struct llc_addr *daddr,
+				    struct llc_addr *laddr, const struct net *net);
+void llc_sap_add_socket(struct llc_sap *sap, struct sock *sk);
+void llc_sap_remove_socket(struct llc_sap *sap, struct sock *sk);
+
+u8 llc_data_accept_state(u8 state);
+void llc_build_offset_table(void);
+#endif /* LLC_CONN_H */