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, 308 insertions, 0 deletions

diff --git a/drivers/acpi/acpica/exdebug.c b/drivers/acpi/acpica/exdebug.c
new file mode 100644
index 000000000..a592bcc5d
--- /dev/null
+++ b/drivers/acpi/acpica/exdebug.c
@@ -0,0 +1,308 @@
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/******************************************************************************
+ *
+ * Module Name: exdebug - Support for stores to the AML Debug Object
+ *
+ * Copyright (C) 2000 - 2026, Intel Corp.
+ *
+ *****************************************************************************/
+
+#include <acpi/acpi.h>
+#include "accommon.h"
+#include "acinterp.h"
+
+#define _COMPONENT          ACPI_EXECUTER
+ACPI_MODULE_NAME("exdebug")
+
+#ifndef ACPI_NO_ERROR_MESSAGES
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ex_do_debug_object
+ *
+ * PARAMETERS:  source_desc         - Object to be output to "Debug Object"
+ *              level               - Indentation level (used for packages)
+ *              index               - Current package element, zero if not pkg
+ *
+ * RETURN:      None
+ *
+ * DESCRIPTION: Handles stores to the AML Debug Object. For example:
+ *              Store(INT1, Debug)
+ *
+ * This function is not compiled if ACPI_NO_ERROR_MESSAGES is set.
+ *
+ * This function is only enabled if acpi_gbl_enable_aml_debug_object is set, or
+ * if ACPI_LV_DEBUG_OBJECT is set in the acpi_dbg_level. Thus, in the normal
+ * operational case, stores to the debug object are ignored but can be easily
+ * enabled if necessary.
+ *
+ ******************************************************************************/
+void
+acpi_ex_do_debug_object(union acpi_operand_object *source_desc,
+			u32 level, u32 index)
+{
+	u32 i;
+	u32 timer;
+	union acpi_operand_object *object_desc;
+	u32 value;
+
+	ACPI_FUNCTION_TRACE_PTR(ex_do_debug_object, source_desc);
+
+	/* Output must be enabled via the debug_object global or the dbg_level */
+
+	if (!acpi_gbl_enable_aml_debug_object &&
+	    !(acpi_dbg_level & ACPI_LV_DEBUG_OBJECT)) {
+		return_VOID;
+	}
+
+	/* Newline -- don't emit the line header */
+
+	if (source_desc &&
+	    (ACPI_GET_DESCRIPTOR_TYPE(source_desc) == ACPI_DESC_TYPE_OPERAND) &&
+	    (source_desc->common.type == ACPI_TYPE_STRING)) {
+		if ((source_desc->string.length == 1) &&
+		    (*source_desc->string.pointer == '\n')) {
+			acpi_os_printf("\n");
+			return_VOID;
+		}
+	}
+
+	/*
+	 * Print line header as long as we are not in the middle of an
+	 * object display
+	 */
+	if (!((level > 0) && index == 0)) {
+		if (acpi_gbl_display_debug_timer) {
+			/*
+			 * We will emit the current timer value (in microseconds) with each
+			 * debug output. Only need the lower 26 bits. This allows for 67
+			 * million microseconds or 67 seconds before rollover.
+			 *
+			 * Convert 100 nanosecond units to microseconds
+			 */
+			timer = ((u32)acpi_os_get_timer() / 10);
+			timer &= 0x03FFFFFF;
+
+			acpi_os_printf("ACPI Debug: T=0x%8.8X %*s", timer,
+				       level, " ");
+		} else {
+			acpi_os_printf("ACPI Debug: %*s", level, " ");
+		}
+	}
+
+	/* Display the index for package output only */
+
+	if (index > 0) {
+		acpi_os_printf("(%.2u) ", index - 1);
+	}
+
+	if (!source_desc) {
+		acpi_os_printf("[Null Object]\n");
+		return_VOID;
+	}
+
+	if (ACPI_GET_DESCRIPTOR_TYPE(source_desc) == ACPI_DESC_TYPE_OPERAND) {
+
+		/* No object type prefix needed for integers and strings */
+
+		if ((source_desc->common.type != ACPI_TYPE_INTEGER) &&
+		    (source_desc->common.type != ACPI_TYPE_STRING)) {
+			acpi_os_printf("%s ",
+				       acpi_ut_get_object_type_name
+				       (source_desc));
+		}
+
+		if (!acpi_ut_valid_internal_object(source_desc)) {
+			acpi_os_printf("%p, Invalid Internal Object!\n",
+				       source_desc);
+			return_VOID;
+		}
+	} else if (ACPI_GET_DESCRIPTOR_TYPE(source_desc) ==
+		   ACPI_DESC_TYPE_NAMED) {
+		acpi_os_printf("%s (Node %p)\n",
+			       acpi_ut_get_type_name(((struct
+						       acpi_namespace_node *)
+						      source_desc)->type),
+			       source_desc);
+		return_VOID;
+	} else {
+		return_VOID;
+	}
+
+	/* source_desc is of type ACPI_DESC_TYPE_OPERAND */
+
+	switch (source_desc->common.type) {
+	case ACPI_TYPE_INTEGER:
+
+		/* Output correct integer width */
+
+		if (acpi_gbl_integer_byte_width == 4) {
+			acpi_os_printf("0x%8.8X\n",
+				       (u32)source_desc->integer.value);
+		} else {
+			acpi_os_printf("0x%8.8X%8.8X\n",
+				       ACPI_FORMAT_UINT64(source_desc->integer.
+							  value));
+		}
+		break;
+
+	case ACPI_TYPE_BUFFER:
+
+		acpi_os_printf("[0x%.2X]\n", (u32)source_desc->buffer.length);
+		acpi_ut_dump_buffer(source_desc->buffer.pointer,
+				    (source_desc->buffer.length < 256) ?
+				    source_desc->buffer.length : 256,
+				    DB_BYTE_DISPLAY, 0);
+		break;
+
+	case ACPI_TYPE_STRING:
+
+		acpi_os_printf("\"%s\"\n", source_desc->string.pointer);
+		break;
+
+	case ACPI_TYPE_PACKAGE:
+
+		acpi_os_printf("(Contains 0x%.2X Elements):\n",
+			       source_desc->package.count);
+
+		/* Output the entire contents of the package */
+
+		for (i = 0; i < source_desc->package.count; i++) {
+			acpi_ex_do_debug_object(source_desc->package.
+						elements[i], level + 4, i + 1);
+		}
+		break;
+
+	case ACPI_TYPE_LOCAL_REFERENCE:
+
+		acpi_os_printf("[%s] ",
+			       acpi_ut_get_reference_name(source_desc));
+
+		/* Decode the reference */
+
+		switch (source_desc->reference.class) {
+		case ACPI_REFCLASS_INDEX:
+
+			acpi_os_printf("0x%X\n", source_desc->reference.value);
+			break;
+
+		case ACPI_REFCLASS_TABLE:
+
+			/* Case for ddb_handle */
+
+			acpi_os_printf("Table Index 0x%X\n",
+				       source_desc->reference.value);
+			return_VOID;
+
+		default:
+
+			break;
+		}
+
+		acpi_os_printf(" ");
+
+		/* Check for valid node first, then valid object */
+
+		if (source_desc->reference.node) {
+			if (ACPI_GET_DESCRIPTOR_TYPE
+			    (source_desc->reference.node) !=
+			    ACPI_DESC_TYPE_NAMED) {
+				acpi_os_printf
+				    (" %p - Not a valid namespace node\n",
+				     source_desc->reference.node);
+			} else {
+				acpi_os_printf("Node %p [%4.4s] ",
+					       source_desc->reference.node,
+					       (source_desc->reference.node)->
+					       name.ascii);
+
+				switch ((source_desc->reference.node)->type) {
+
+					/* These types have no attached object */
+
+				case ACPI_TYPE_DEVICE:
+					acpi_os_printf("Device\n");
+					break;
+
+				case ACPI_TYPE_THERMAL:
+					acpi_os_printf("Thermal Zone\n");
+					break;
+
+				default:
+
+					acpi_ex_do_debug_object((source_desc->
+								 reference.
+								 node)->object,
+								level + 4, 0);
+					break;
+				}
+			}
+		} else if (source_desc->reference.object) {
+			if (ACPI_GET_DESCRIPTOR_TYPE
+			    (source_desc->reference.object) ==
+			    ACPI_DESC_TYPE_NAMED) {
+
+				/* Reference object is a namespace node */
+
+				acpi_ex_do_debug_object(ACPI_CAST_PTR
+							(union
+							 acpi_operand_object,
+							 source_desc->reference.
+							 object), level + 4, 0);
+			} else {
+				object_desc = source_desc->reference.object;
+				value = source_desc->reference.value;
+
+				switch (object_desc->common.type) {
+				case ACPI_TYPE_BUFFER:
+
+					acpi_os_printf("Buffer[%u] = 0x%2.2X\n",
+						       value,
+						       *source_desc->reference.
+						       index_pointer);
+					break;
+
+				case ACPI_TYPE_STRING:
+
+					acpi_os_printf
+					    ("String[%u] = \"%c\" (0x%2.2X)\n",
+					     value,
+					     *source_desc->reference.
+					     index_pointer,
+					     *source_desc->reference.
+					     index_pointer);
+					break;
+
+				case ACPI_TYPE_PACKAGE:
+
+					acpi_os_printf("Package[%u] = ", value);
+					if (!(*source_desc->reference.where)) {
+						acpi_os_printf
+						    ("[Uninitialized Package Element]\n");
+					} else {
+						acpi_ex_do_debug_object
+						    (*source_desc->reference.
+						     where, level + 4, 0);
+					}
+					break;
+
+				default:
+
+					acpi_os_printf
+					    ("Unknown Reference object type %X\n",
+					     object_desc->common.type);
+					break;
+				}
+			}
+		}
+		break;
+
+	default:
+
+		acpi_os_printf("(Descriptor %p)\n", source_desc);
+		break;
+	}
+
+	ACPI_DEBUG_PRINT_RAW((ACPI_DB_EXEC, "\n"));
+	return_VOID;
+}
+#endif