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, 187 insertions, 0 deletions

diff --git a/net/wireless/sysfs.c b/net/wireless/sysfs.c
new file mode 100644
index 000000000..3ec25d3f0
--- /dev/null
+++ b/net/wireless/sysfs.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This file provides /sys/class/ieee80211/<wiphy name>/
+ * and some default attributes.
+ *
+ * Copyright 2005-2006	Jiri Benc <jbenc@suse.cz>
+ * Copyright 2006	Johannes Berg <johannes@sipsolutions.net>
+ * Copyright (C) 2020-2021, 2023-2024 Intel Corporation
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/nl80211.h>
+#include <linux/rtnetlink.h>
+#include <net/cfg80211.h>
+#include "sysfs.h"
+#include "core.h"
+#include "rdev-ops.h"
+
+static inline struct cfg80211_registered_device *dev_to_rdev(
+	struct device *dev)
+{
+	return container_of(dev, struct cfg80211_registered_device, wiphy.dev);
+}
+
+#define SHOW_FMT(name, fmt, member)					\
+static ssize_t name ## _show(struct device *dev,			\
+			      struct device_attribute *attr,		\
+			      char *buf)				\
+{									\
+	return sprintf(buf, fmt "\n", dev_to_rdev(dev)->member);	\
+}									\
+static DEVICE_ATTR_RO(name)
+
+SHOW_FMT(index, "%d", wiphy_idx);
+SHOW_FMT(macaddress, "%pM", wiphy.perm_addr);
+SHOW_FMT(address_mask, "%pM", wiphy.addr_mask);
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr,
+			 char *buf)
+{
+	struct wiphy *wiphy = &dev_to_rdev(dev)->wiphy;
+
+	return sprintf(buf, "%s\n", wiphy_name(wiphy));
+}
+static DEVICE_ATTR_RO(name);
+
+static ssize_t addresses_show(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct wiphy *wiphy = &dev_to_rdev(dev)->wiphy;
+	char *start = buf;
+	int i;
+
+	if (!wiphy->addresses)
+		return sprintf(buf, "%pM\n", wiphy->perm_addr);
+
+	for (i = 0; i < wiphy->n_addresses; i++)
+		buf += sprintf(buf, "%pM\n", wiphy->addresses[i].addr);
+
+	return buf - start;
+}
+static DEVICE_ATTR_RO(addresses);
+
+static struct attribute *ieee80211_attrs[] = {
+	&dev_attr_index.attr,
+	&dev_attr_macaddress.attr,
+	&dev_attr_address_mask.attr,
+	&dev_attr_addresses.attr,
+	&dev_attr_name.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(ieee80211);
+
+static void wiphy_dev_release(struct device *dev)
+{
+	struct cfg80211_registered_device *rdev = dev_to_rdev(dev);
+
+	cfg80211_dev_free(rdev);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static void cfg80211_leave_all(struct cfg80211_registered_device *rdev)
+{
+	struct wireless_dev *wdev;
+
+	list_for_each_entry(wdev, &rdev->wiphy.wdev_list, list)
+		cfg80211_leave(rdev, wdev, -1);
+}
+
+static int wiphy_suspend(struct device *dev)
+{
+	struct cfg80211_registered_device *rdev = dev_to_rdev(dev);
+	int ret = 0;
+
+	rdev->suspend_at = ktime_get_boottime_seconds();
+
+	rtnl_lock();
+	if (!rdev->wiphy.registered)
+		goto out_unlock_rtnl;
+
+	if (rdev->wiphy.wowlan_config) {
+		scoped_guard(wiphy, &rdev->wiphy) {
+			cfg80211_process_wiphy_works(rdev, NULL);
+			if (rdev->ops->suspend)
+				ret = rdev_suspend(rdev,
+						   rdev->wiphy.wowlan_config);
+			if (ret <= 0)
+				goto out_unlock_rtnl;
+		}
+	}
+
+	/* Driver refused to configure wowlan (ret = 1) or no wowlan */
+
+	cfg80211_leave_all(rdev);
+	scoped_guard(wiphy, &rdev->wiphy) {
+		cfg80211_process_rdev_events(rdev);
+		cfg80211_process_wiphy_works(rdev, NULL);
+		if (rdev->ops->suspend)
+			ret = rdev_suspend(rdev, NULL);
+	}
+out_unlock_rtnl:
+	if (ret == 0)
+		rdev->suspended = true;
+	rtnl_unlock();
+
+	return ret;
+}
+
+static int wiphy_resume(struct device *dev)
+{
+	struct cfg80211_registered_device *rdev = dev_to_rdev(dev);
+	int ret = 0;
+
+	/* Age scan results with time spent in suspend */
+	cfg80211_bss_age(rdev, ktime_get_boottime_seconds() - rdev->suspend_at);
+
+	rtnl_lock();
+	wiphy_lock(&rdev->wiphy);
+	if (rdev->wiphy.registered && rdev->ops->resume)
+		ret = rdev_resume(rdev);
+	rdev->suspended = false;
+	queue_work(system_dfl_wq, &rdev->wiphy_work);
+	wiphy_unlock(&rdev->wiphy);
+
+	if (ret)
+		cfg80211_shutdown_all_interfaces(&rdev->wiphy);
+
+	rtnl_unlock();
+
+	return ret;
+}
+
+static SIMPLE_DEV_PM_OPS(wiphy_pm_ops, wiphy_suspend, wiphy_resume);
+#define WIPHY_PM_OPS (&wiphy_pm_ops)
+#else
+#define WIPHY_PM_OPS NULL
+#endif
+
+static const struct ns_common *wiphy_namespace(const struct device *d)
+{
+	struct wiphy *wiphy = container_of(d, struct wiphy, dev);
+
+	return to_ns_common(wiphy_net(wiphy));
+}
+
+struct class ieee80211_class = {
+	.name = "ieee80211",
+	.dev_release = wiphy_dev_release,
+	.dev_groups = ieee80211_groups,
+	.pm = WIPHY_PM_OPS,
+	.ns_type = &net_ns_type_operations,
+	.namespace = wiphy_namespace,
+};
+
+int wiphy_sysfs_init(void)
+{
+	return class_register(&ieee80211_class);
+}
+
+void wiphy_sysfs_exit(void)
+{
+	class_unregister(&ieee80211_class);
+}