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, 141 insertions, 0 deletions

diff --git a/net/wireless/wext-proc.c b/net/wireless/wext-proc.c
new file mode 100644
index 000000000..be6b2b695
--- /dev/null
+++ b/net/wireless/wext-proc.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This file implement the Wireless Extensions proc API.
+ *
+ * Authors :	Jean Tourrilhes - HPL - <jt@hpl.hp.com>
+ * Copyright (c) 1997-2007 Jean Tourrilhes, All Rights Reserved.
+ */
+
+/*
+ * The /proc/net/wireless file is a human readable user-space interface
+ * exporting various wireless specific statistics from the wireless devices.
+ * This is the most popular part of the Wireless Extensions ;-)
+ *
+ * This interface is a pure clone of /proc/net/dev (in net/core/dev.c).
+ * The content of the file is basically the content of "struct iw_statistics".
+ */
+
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/wireless.h>
+#include <linux/netdevice.h>
+#include <linux/rtnetlink.h>
+#include <net/iw_handler.h>
+#include <net/wext.h>
+
+
+static void wireless_seq_printf_stats(struct seq_file *seq,
+				      struct net_device *dev)
+{
+	/* Get stats from the driver */
+	struct iw_statistics *stats = get_wireless_stats(dev);
+	static struct iw_statistics nullstats = {};
+
+	/* show device if it's wireless regardless of current stats */
+	if (!stats) {
+#ifdef CONFIG_WIRELESS_EXT
+		if (dev->wireless_handlers)
+			stats = &nullstats;
+#endif
+#ifdef CONFIG_CFG80211
+		if (dev->ieee80211_ptr)
+			stats = &nullstats;
+#endif
+	}
+
+	if (stats) {
+		seq_printf(seq, "%6s: %04x  %3d%c  %3d%c  %3d%c  %6d %6d %6d "
+				"%6d %6d   %6d\n",
+			   dev->name, stats->status, stats->qual.qual,
+			   stats->qual.updated & IW_QUAL_QUAL_UPDATED
+			   ? '.' : ' ',
+			   ((__s32) stats->qual.level) -
+			   ((stats->qual.updated & IW_QUAL_DBM) ? 0x100 : 0),
+			   stats->qual.updated & IW_QUAL_LEVEL_UPDATED
+			   ? '.' : ' ',
+			   ((__s32) stats->qual.noise) -
+			   ((stats->qual.updated & IW_QUAL_DBM) ? 0x100 : 0),
+			   stats->qual.updated & IW_QUAL_NOISE_UPDATED
+			   ? '.' : ' ',
+			   stats->discard.nwid, stats->discard.code,
+			   stats->discard.fragment, stats->discard.retries,
+			   stats->discard.misc, stats->miss.beacon);
+
+		if (stats != &nullstats)
+			stats->qual.updated &= ~IW_QUAL_ALL_UPDATED;
+	}
+}
+
+/* ---------------------------------------------------------------- */
+/*
+ * Print info for /proc/net/wireless (print all entries)
+ */
+static int wireless_dev_seq_show(struct seq_file *seq, void *v)
+{
+	might_sleep();
+
+	if (v == SEQ_START_TOKEN)
+		seq_printf(seq, "Inter-| sta-|   Quality        |   Discarded "
+				"packets               | Missed | WE\n"
+				" face | tus | link level noise |  nwid  "
+				"crypt   frag  retry   misc | beacon | %d\n",
+			   WIRELESS_EXT);
+	else
+		wireless_seq_printf_stats(seq, v);
+	return 0;
+}
+
+static void *wireless_dev_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct net *net = seq_file_net(seq);
+	loff_t off;
+	struct net_device *dev;
+
+	rtnl_lock();
+	if (!*pos)
+		return SEQ_START_TOKEN;
+
+	off = 1;
+	for_each_netdev(net, dev)
+		if (off++ == *pos)
+			return dev;
+	return NULL;
+}
+
+static void *wireless_dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct net *net = seq_file_net(seq);
+
+	++*pos;
+
+	return v == SEQ_START_TOKEN ?
+		first_net_device(net) : next_net_device(v);
+}
+
+static void wireless_dev_seq_stop(struct seq_file *seq, void *v)
+{
+	rtnl_unlock();
+}
+
+static const struct seq_operations wireless_seq_ops = {
+	.start = wireless_dev_seq_start,
+	.next  = wireless_dev_seq_next,
+	.stop  = wireless_dev_seq_stop,
+	.show  = wireless_dev_seq_show,
+};
+
+int __net_init wext_proc_init(struct net *net)
+{
+	/* Create /proc/net/wireless entry */
+	if (!proc_create_net("wireless", 0444, net->proc_net,
+			&wireless_seq_ops, sizeof(struct seq_net_private)))
+		return -ENOMEM;
+
+	return 0;
+}
+
+void __net_exit wext_proc_exit(struct net *net)
+{
+	remove_proc_entry("wireless", net->proc_net);
+}