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, 138 insertions, 0 deletions

diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
new file mode 100644
index 000000000..ffda15318
--- /dev/null
+++ b/include/net/netns/ipv6.h
@@ -0,0 +1,138 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * ipv6 in net namespaces
+ */
+
+#include <net/inet_frag.h>
+
+#ifndef __NETNS_IPV6_H__
+#define __NETNS_IPV6_H__
+#include <net/dst_ops.h>
+#include <uapi/linux/icmpv6.h>
+
+struct ctl_table_header;
+
+struct netns_sysctl_ipv6 {
+#ifdef CONFIG_SYSCTL
+	struct ctl_table_header *hdr;
+	struct ctl_table_header *route_hdr;
+	struct ctl_table_header *icmp_hdr;
+	struct ctl_table_header *frags_hdr;
+	struct ctl_table_header *xfrm6_hdr;
+#endif
+	int flush_delay;
+	int ip6_rt_max_size;
+	int ip6_rt_gc_min_interval;
+	int ip6_rt_gc_timeout;
+	int ip6_rt_gc_interval;
+	int ip6_rt_gc_elasticity;
+	int ip6_rt_mtu_expires;
+	int ip6_rt_min_advmss;
+	u32 multipath_hash_fields;
+	u8 multipath_hash_policy;
+
+	__cacheline_group_begin(sysctl_ipv6_flowlabel);
+	u8 flowlabel_consistency;
+	u8 auto_flowlabels;
+	u8 flowlabel_state_ranges;
+	__cacheline_group_end(sysctl_ipv6_flowlabel);
+
+	u8 icmpv6_echo_ignore_all;
+	u8 icmpv6_echo_ignore_multicast;
+	u8 icmpv6_echo_ignore_anycast;
+	int icmpv6_time;
+	DECLARE_BITMAP(icmpv6_ratemask, ICMPV6_MSG_MAX + 1);
+	unsigned long *icmpv6_ratemask_ptr;
+	u8 anycast_src_echo_reply;
+	u8 bindv6only;
+	u8 ip_nonlocal_bind;
+	u8 fwmark_reflect;
+	int idgen_retries;
+	int idgen_delay;
+	int flowlabel_reflect;
+	int max_dst_opts_cnt;
+	int max_hbh_opts_cnt;
+	int max_dst_opts_len;
+	int max_hbh_opts_len;
+	int seg6_flowlabel;
+	u32 ioam6_id;
+	u64 ioam6_id_wide;
+	u8 skip_notify_on_dev_down;
+	u8 fib_notify_on_flag_change;
+	u8 icmpv6_error_anycast_as_unicast;
+	u8 icmpv6_errors_extension_mask;
+};
+
+struct netns_ipv6 {
+	/* Keep ip6_dst_ops at the beginning of netns_sysctl_ipv6 */
+	struct dst_ops		ip6_dst_ops;
+
+	struct netns_sysctl_ipv6 sysctl;
+	struct ipv6_devconf	*devconf_all;
+	struct ipv6_devconf	*devconf_dflt;
+	struct inet_peer_base	*peers;
+	struct fqdir		*fqdir;
+	struct fib6_info	*fib6_null_entry;
+	struct rt6_info		*ip6_null_entry;
+	struct rt6_statistics   *rt6_stats;
+	struct timer_list       ip6_fib_timer;
+	struct hlist_head       *fib_table_hash;
+	spinlock_t		fib_table_hash_lock;
+	struct fib6_table       *fib6_main_tbl;
+	struct list_head	fib6_walkers;
+	rwlock_t		fib6_walker_lock;
+	spinlock_t		fib6_gc_lock;
+	atomic_t		ip6_rt_gc_expire;
+	unsigned long		ip6_rt_last_gc;
+	unsigned char		flowlabel_has_excl;
+#ifdef CONFIG_IPV6_MULTIPLE_TABLES
+	bool			fib6_has_custom_rules;
+	unsigned int		fib6_rules_require_fldissect;
+#ifdef CONFIG_IPV6_SUBTREES
+	unsigned int		fib6_routes_require_src;
+#endif
+	struct rt6_info         *ip6_prohibit_entry;
+	struct rt6_info         *ip6_blk_hole_entry;
+	struct fib6_table       *fib6_local_tbl;
+	struct fib_rules_ops    *fib6_rules_ops;
+#endif
+	struct sock             *ndisc_sk;
+	struct sock             *tcp_sk;
+	struct sock             *igmp_sk;
+	struct sock		*mc_autojoin_sk;
+
+	struct hlist_head	*inet6_addr_lst;
+	spinlock_t		addrconf_hash_lock;
+	struct delayed_work	addr_chk_work;
+
+#ifdef CONFIG_IPV6_MROUTE
+#ifndef CONFIG_IPV6_MROUTE_MULTIPLE_TABLES
+	struct mr_table		*mrt6;
+#else
+	struct list_head	mr6_tables;
+	struct fib_rules_ops	*mr6_rules_ops;
+#endif
+	struct fib_notifier_ops	*ip6mr_notifier_ops;
+	atomic_t		ipmr_seq;
+	struct mutex		mfc_mutex;
+#endif
+	atomic_t		dev_addr_genid;
+	atomic_t		fib6_sernum;
+	struct seg6_pernet_data *seg6_data;
+	struct fib_notifier_ops	*notifier_ops;
+	int			flowlabel_count;
+	struct {
+		struct hlist_head head;
+		spinlock_t	lock;
+		u32		seq;
+	} ip6addrlbl_table;
+	struct ioam6_pernet_data *ioam6_data;
+};
+
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+struct netns_nf_frag {
+	struct fqdir	*fqdir;
+};
+#endif
+
+#endif