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, 122 insertions, 0 deletions

diff --git a/drivers/input/apm-power.c b/drivers/input/apm-power.c
new file mode 100644
index 000000000..028fcaf4c
--- /dev/null
+++ b/drivers/input/apm-power.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Input Power Event -> APM Bridge
+ *
+ *  Copyright (c) 2007 Richard Purdie
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/tty.h>
+#include <linux/delay.h>
+#include <linux/pm.h>
+#include <linux/apm-emulation.h>
+
+static void system_power_event(unsigned int keycode)
+{
+	switch (keycode) {
+	case KEY_SUSPEND:
+		apm_queue_event(APM_USER_SUSPEND);
+		pr_info("Requesting system suspend...\n");
+		break;
+	default:
+		break;
+	}
+}
+
+static void apmpower_event(struct input_handle *handle, unsigned int type,
+			   unsigned int code, int value)
+{
+	/* only react on key down events */
+	if (value != 1)
+		return;
+
+	switch (type) {
+	case EV_PWR:
+		system_power_event(code);
+		break;
+
+	default:
+		break;
+	}
+}
+
+static int apmpower_connect(struct input_handler *handler,
+					  struct input_dev *dev,
+					  const struct input_device_id *id)
+{
+	struct input_handle *handle;
+	int error;
+
+	handle = kzalloc_obj(struct input_handle);
+	if (!handle)
+		return -ENOMEM;
+
+	handle->dev = dev;
+	handle->handler = handler;
+	handle->name = "apm-power";
+
+	error = input_register_handle(handle);
+	if (error) {
+		pr_err("Failed to register input power handler, error %d\n",
+		       error);
+		kfree(handle);
+		return error;
+	}
+
+	error = input_open_device(handle);
+	if (error) {
+		pr_err("Failed to open input power device, error %d\n", error);
+		input_unregister_handle(handle);
+		kfree(handle);
+		return error;
+	}
+
+	return 0;
+}
+
+static void apmpower_disconnect(struct input_handle *handle)
+{
+	input_close_device(handle);
+	input_unregister_handle(handle);
+	kfree(handle);
+}
+
+static const struct input_device_id apmpower_ids[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_PWR) },
+	},
+	{ },
+};
+
+MODULE_DEVICE_TABLE(input, apmpower_ids);
+
+static struct input_handler apmpower_handler = {
+	.event =	apmpower_event,
+	.connect =	apmpower_connect,
+	.disconnect =	apmpower_disconnect,
+	.name =		"apm-power",
+	.id_table =	apmpower_ids,
+};
+
+static int __init apmpower_init(void)
+{
+	return input_register_handler(&apmpower_handler);
+}
+
+static void __exit apmpower_exit(void)
+{
+	input_unregister_handler(&apmpower_handler);
+}
+
+module_init(apmpower_init);
+module_exit(apmpower_exit);
+
+MODULE_AUTHOR("Richard Purdie <rpurdie@rpsys.net>");
+MODULE_DESCRIPTION("Input Power Event -> APM Bridge");
+MODULE_LICENSE("GPL");