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, 304 insertions, 0 deletions

diff --git a/net/wireless/debugfs.c b/net/wireless/debugfs.c
new file mode 100644
index 000000000..f9e7fff1e
--- /dev/null
+++ b/net/wireless/debugfs.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * cfg80211 debugfs
+ *
+ * Copyright 2009	Luis R. Rodriguez <lrodriguez@atheros.com>
+ * Copyright 2007	Johannes Berg <johannes@sipsolutions.net>
+ * Copyright (C) 2023 Intel Corporation
+ */
+
+#include <linux/slab.h>
+#include "core.h"
+#include "debugfs.h"
+
+#define DEBUGFS_READONLY_FILE(name, buflen, fmt, value...)		\
+static ssize_t name## _read(struct file *file, char __user *userbuf,	\
+			    size_t count, loff_t *ppos)			\
+{									\
+	struct wiphy *wiphy = file->private_data;			\
+	char buf[buflen];						\
+	int res;							\
+									\
+	res = scnprintf(buf, buflen, fmt "\n", ##value);		\
+	return simple_read_from_buffer(userbuf, count, ppos, buf, res);	\
+}									\
+									\
+static const struct file_operations name## _ops = {			\
+	.read = name## _read,						\
+	.open = simple_open,						\
+	.llseek = generic_file_llseek,					\
+}
+
+#define DEBUGFS_RADIO_READONLY_FILE(name, buflen, fmt, value...)	\
+static ssize_t name## _read(struct file *file, char __user *userbuf,	\
+			    size_t count, loff_t *ppos)			\
+{									\
+	struct wiphy_radio_cfg *radio_cfg = file->private_data;		\
+	char buf[buflen];						\
+	int res;							\
+									\
+	res = scnprintf(buf, buflen, fmt "\n", ##value);		\
+	return simple_read_from_buffer(userbuf, count, ppos, buf, res);	\
+}									\
+									\
+static const struct file_operations name## _ops = {			\
+	.read = name## _read,						\
+	.open = simple_open,						\
+	.llseek = generic_file_llseek,					\
+}
+
+DEBUGFS_READONLY_FILE(rts_threshold, 20, "%d",
+		      wiphy->rts_threshold);
+DEBUGFS_READONLY_FILE(fragmentation_threshold, 20, "%d",
+		      wiphy->frag_threshold);
+DEBUGFS_READONLY_FILE(short_retry_limit, 20, "%d",
+		      wiphy->retry_short);
+DEBUGFS_READONLY_FILE(long_retry_limit, 20, "%d",
+		      wiphy->retry_long);
+
+DEBUGFS_RADIO_READONLY_FILE(radio_rts_threshold, 20, "%d",
+			    radio_cfg->rts_threshold);
+
+static int ht_print_chan(struct ieee80211_channel *chan,
+			 char *buf, int buf_size, int offset)
+{
+	if (WARN_ON(offset > buf_size))
+		return 0;
+
+	if (chan->flags & IEEE80211_CHAN_DISABLED)
+		return scnprintf(buf + offset,
+				 buf_size - offset,
+				 "%d Disabled\n",
+				 chan->center_freq);
+
+	return scnprintf(buf + offset,
+			 buf_size - offset,
+			 "%d HT40 %c%c\n",
+			 chan->center_freq,
+			 (chan->flags & IEEE80211_CHAN_NO_HT40MINUS) ?
+				' ' : '-',
+			 (chan->flags & IEEE80211_CHAN_NO_HT40PLUS) ?
+				' ' : '+');
+}
+
+static ssize_t ht40allow_map_read(struct file *file,
+				  char __user *user_buf,
+				  size_t count, loff_t *ppos)
+{
+	struct wiphy *wiphy = file->private_data;
+	char *buf;
+	unsigned int offset = 0, buf_size = PAGE_SIZE, i;
+	enum nl80211_band band;
+	struct ieee80211_supported_band *sband;
+	ssize_t r;
+
+	buf = kzalloc(buf_size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (band = 0; band < NUM_NL80211_BANDS; band++) {
+		sband = wiphy->bands[band];
+		if (!sband)
+			continue;
+		for (i = 0; i < sband->n_channels; i++)
+			offset += ht_print_chan(&sband->channels[i],
+						buf, buf_size, offset);
+	}
+
+	r = simple_read_from_buffer(user_buf, count, ppos, buf, offset);
+
+	kfree(buf);
+
+	return r;
+}
+
+static const struct file_operations ht40allow_map_ops = {
+	.read = ht40allow_map_read,
+	.open = simple_open,
+	.llseek = default_llseek,
+};
+
+#define DEBUGFS_ADD(name)						\
+	debugfs_create_file(#name, 0444, phyd, &rdev->wiphy, &name## _ops)
+
+#define DEBUGFS_RADIO_ADD(name, radio_idx)				\
+	debugfs_create_file(#name, 0444, radiod,			\
+			    &rdev->wiphy.radio_cfg[radio_idx],		\
+			    &name## _ops)
+
+void cfg80211_debugfs_rdev_add(struct cfg80211_registered_device *rdev)
+{
+	struct dentry *phyd = rdev->wiphy.debugfsdir;
+	struct dentry *radiod;
+	u8 i;
+
+	DEBUGFS_ADD(rts_threshold);
+	DEBUGFS_ADD(fragmentation_threshold);
+	DEBUGFS_ADD(short_retry_limit);
+	DEBUGFS_ADD(long_retry_limit);
+	DEBUGFS_ADD(ht40allow_map);
+
+	for (i = 0; i < rdev->wiphy.n_radio; i++) {
+		radiod = rdev->wiphy.radio_cfg[i].radio_debugfsdir;
+		DEBUGFS_RADIO_ADD(radio_rts_threshold, i);
+	}
+}
+
+struct debugfs_read_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t bufsize;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_read_work(struct wiphy *wiphy,
+					   struct wiphy_work *work)
+{
+	struct debugfs_read_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->bufsize, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_read_cancel(struct dentry *dentry,
+					     void *data)
+{
+	struct debugfs_read_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_read(struct wiphy *wiphy, struct file *file,
+				  char *buf, size_t bufsize,
+				  char __user *userbuf, size_t count,
+				  loff_t *ppos,
+				  ssize_t (*handler)(struct wiphy *wiphy,
+						     struct file *file,
+						     char *buf,
+						     size_t bufsize,
+						     void *data),
+				  void *data)
+{
+	struct debugfs_read_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.bufsize = bufsize,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_read_cancel,
+		.cancel_data = &work,
+	};
+
+	/* don't leak stack data or whatever */
+	memset(buf, 0, bufsize);
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_read_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	if (work.ret < 0)
+		return work.ret;
+
+	if (WARN_ON(work.ret > bufsize))
+		return -EINVAL;
+
+	return simple_read_from_buffer(userbuf, count, ppos, buf, work.ret);
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_read);
+
+struct debugfs_write_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t count;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_write_work(struct wiphy *wiphy,
+					    struct wiphy_work *work)
+{
+	struct debugfs_write_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->count, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_write_cancel(struct dentry *dentry,
+					      void *data)
+{
+	struct debugfs_write_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_write(struct wiphy *wiphy,
+				   struct file *file, char *buf, size_t bufsize,
+				   const char __user *userbuf, size_t count,
+				   ssize_t (*handler)(struct wiphy *wiphy,
+						      struct file *file,
+						      char *buf,
+						      size_t count,
+						      void *data),
+				   void *data)
+{
+	struct debugfs_write_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.count = count,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_write_cancel,
+		.cancel_data = &work,
+	};
+
+	/* mostly used for strings so enforce NUL-termination for safety */
+	if (count >= bufsize)
+		return -EINVAL;
+
+	memset(buf, 0, bufsize);
+
+	if (copy_from_user(buf, userbuf, count))
+		return -EFAULT;
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_write_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	return work.ret;
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_write);