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, 332 insertions, 0 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
new file mode 100644
index 000000000..8d4db2241
--- /dev/null
+++ b/tools/testing/selftests/Makefile
@@ -0,0 +1,332 @@
+# SPDX-License-Identifier: GPL-2.0
+TARGETS += acct
+TARGETS += alsa
+TARGETS += amd-pstate
+TARGETS += arm64
+TARGETS += bpf
+TARGETS += breakpoints
+TARGETS += cachestat
+TARGETS += capabilities
+TARGETS += cgroup
+TARGETS += clone3
+TARGETS += connector
+TARGETS += core
+TARGETS += cpufreq
+TARGETS += cpu-hotplug
+TARGETS += damon
+TARGETS += devices/error_logs
+TARGETS += devices/probe
+TARGETS += dmabuf-heaps
+TARGETS += drivers/dma-buf
+TARGETS += drivers/ntsync
+TARGETS += drivers/s390x/uvdevice
+TARGETS += drivers/net
+TARGETS += drivers/net/bonding
+TARGETS += drivers/net/netconsole
+TARGETS += drivers/net/team
+TARGETS += drivers/net/virtio_net
+TARGETS += drivers/platform/x86/intel/ifs
+TARGETS += dt
+TARGETS += efivarfs
+TARGETS += exec
+TARGETS += fchmodat2
+TARGETS += filesystems
+TARGETS += filesystems/binderfs
+TARGETS += filesystems/epoll
+TARGETS += filesystems/fat
+TARGETS += filesystems/overlayfs
+TARGETS += filesystems/statmount
+TARGETS += filesystems/mount-notify
+TARGETS += filesystems/nsfs
+TARGETS += filesystems/fuse
+TARGETS += filesystems/move_mount
+TARGETS += filesystems/empty_mntns
+TARGETS += filesystems/fsmount_ns
+TARGETS += firmware
+TARGETS += fpu
+TARGETS += ftrace
+TARGETS += futex
+TARGETS += gpio
+TARGETS += hid
+TARGETS += intel_pstate
+TARGETS += iommu
+TARGETS += ipc
+TARGETS += ir
+TARGETS += kcmp
+TARGETS += kexec
+TARGETS += kselftest_harness
+TARGETS += kvm
+TARGETS += landlock
+TARGETS += lib
+TARGETS += livepatch
+TARGETS += liveupdate
+TARGETS += lkdtm
+TARGETS += lsm
+TARGETS += membarrier
+TARGETS += memfd
+TARGETS += memory-hotplug
+TARGETS += mincore
+TARGETS += mount
+TARGETS += mount_setattr
+TARGETS += move_mount_set_group
+TARGETS += mqueue
+TARGETS += mseal_system_mappings
+TARGETS += nci
+TARGETS += net
+TARGETS += net/af_unix
+TARGETS += net/can
+TARGETS += net/forwarding
+TARGETS += net/hsr
+TARGETS += net/mptcp
+TARGETS += net/netfilter
+TARGETS += net/openvswitch
+TARGETS += net/ovpn
+TARGETS += net/packetdrill
+TARGETS += net/ppp
+TARGETS += net/rds
+TARGETS += net/tcp_ao
+TARGETS += nolibc
+TARGETS += pci_endpoint
+TARGETS += pcie_bwctrl
+TARGETS += perf_events
+TARGETS += pidfd
+TARGETS += pid_namespace
+TARGETS += pipe
+TARGETS += power_supply
+TARGETS += powerpc
+TARGETS += prctl
+TARGETS += proc
+TARGETS += pstore
+TARGETS += ptrace
+TARGETS += openat2
+TARGETS += rdma
+TARGETS += resctrl
+TARGETS += riscv
+TARGETS += rlimits
+TARGETS += rseq
+TARGETS += rtc
+TARGETS += rust
+TARGETS += sched_ext
+TARGETS += seccomp
+TARGETS += sgx
+TARGETS += signal
+TARGETS += size
+TARGETS += sparc64
+TARGETS += splice
+TARGETS += static_keys
+TARGETS += sync
+TARGETS += syscall_user_dispatch
+TARGETS += sysctl
+TARGETS += tc-testing
+TARGETS += tdx
+TARGETS += thermal/intel/power_floor
+TARGETS += thermal/intel/workload_hint
+TARGETS += timens
+ifneq (1, $(quicktest))
+TARGETS += timers
+endif
+TARGETS += tmpfs
+TARGETS += tpm2
+TARGETS += tty
+TARGETS += ublk
+TARGETS += uevent
+TARGETS += user_events
+TARGETS += vDSO
+TARGETS += mm
+TARGETS += vfio
+TARGETS += x86
+TARGETS += x86/bugs
+TARGETS += zram
+#Please keep the TARGETS list alphabetically sorted
+# Run "make quicktest=1 run_tests" or
+# "make quicktest=1 kselftest" from top level Makefile
+
+TARGETS_HOTPLUG = cpu-hotplug
+TARGETS_HOTPLUG += memory-hotplug
+
+# Networking tests want the net/lib target, include it automatically
+ifneq ($(filter net drivers/net drivers/net/hw,$(TARGETS)),)
+ifeq ($(filter net/lib,$(TARGETS)),)
+	INSTALL_DEP_TARGETS := net/lib
+endif
+endif
+
+# User can optionally provide a TARGETS skiplist. By default we skip
+# targets using BPF since it has cutting edge build time dependencies
+# which require more effort to install.
+SKIP_TARGETS ?= bpf sched_ext
+ifneq ($(SKIP_TARGETS),)
+	TMP := $(filter-out $(SKIP_TARGETS), $(TARGETS))
+	override TARGETS := $(TMP)
+endif
+
+# User can set FORCE_TARGETS to 1 to require all targets to be successfully
+# built; make will fail if any of the targets cannot be built. If
+# FORCE_TARGETS is not set (the default), make will succeed if at least one
+# of the targets gets built.
+FORCE_TARGETS ?=
+
+# Clear LDFLAGS and MAKEFLAGS when implicit rules are missing.  This provides
+# implicit rules to sub-test Makefiles which avoids build failures in test
+# Makefile that don't have explicit build rules.
+ifeq (,$(LINK.c))
+override LDFLAGS =
+override MAKEFLAGS =
+endif
+
+# Append kselftest to KBUILD_OUTPUT and O to avoid cluttering
+# KBUILD_OUTPUT with selftest objects and headers installed
+# by selftests Makefile or lib.mk.
+ifdef building_out_of_srctree
+override LDFLAGS =
+endif
+
+top_srcdir ?= ../../..
+
+ifeq ("$(origin O)", "command line")
+  KBUILD_OUTPUT := $(O)
+endif
+
+ifneq ($(KBUILD_OUTPUT),)
+  # Make's built-in functions such as $(abspath ...), $(realpath ...) cannot
+  # expand a shell special character '~'. We use a somewhat tedious way here.
+  abs_objtree := $(shell cd $(top_srcdir) && mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) && pwd)
+  $(if $(abs_objtree),, \
+    $(error failed to create output directory "$(KBUILD_OUTPUT)"))
+  # $(realpath ...) resolves symlinks
+  abs_objtree := $(realpath $(abs_objtree))
+  BUILD := $(abs_objtree)/kselftest
+  KHDR_INCLUDES := -isystem ${abs_objtree}/usr/include
+else
+  BUILD := $(CURDIR)
+  abs_srctree := $(shell cd $(top_srcdir) && pwd)
+  KHDR_INCLUDES := -isystem ${abs_srctree}/usr/include
+  DEFAULT_INSTALL_HDR_PATH := 1
+endif
+
+# Prepare for headers install
+include $(top_srcdir)/scripts/subarch.include
+ARCH           ?= $(SUBARCH)
+export BUILD
+export KHDR_INCLUDES
+
+# set default goal to all, so make without a target runs all, even when
+# all isn't the first target in the file.
+.DEFAULT_GOAL := all
+
+all:
+	@ret=1;							\
+	for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do	\
+		BUILD_TARGET=$$BUILD/$$TARGET;			\
+		mkdir $$BUILD_TARGET  -p;			\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET	\
+				O=$(abs_objtree)		\
+				$(if $(FORCE_TARGETS),|| exit);	\
+		ret=$$((ret * $$?));				\
+	done; exit $$ret;
+
+run_tests: all
+	@for TARGET in $(TARGETS); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET run_tests \
+				SRC_PATH=$(shell readlink -e $$(pwd)) \
+				OBJ_PATH=$(BUILD)                   \
+				O=$(abs_objtree);		    \
+	done;
+
+hotplug:
+	@for TARGET in $(TARGETS_HOTPLUG); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET;\
+	done;
+
+run_hotplug: hotplug
+	@for TARGET in $(TARGETS_HOTPLUG); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET run_full_test;\
+	done;
+
+clean_hotplug:
+	@for TARGET in $(TARGETS_HOTPLUG); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET clean;\
+	done;
+
+run_pstore_crash:
+	$(MAKE) -C pstore run_crash
+
+# Use $BUILD as the default install root. $BUILD points to the
+# right output location for the following cases:
+# 1. output_dir=kernel_src
+# 2. a separate output directory is specified using O= KBUILD_OUTPUT
+# 3. a separate output directory is specified using KBUILD_OUTPUT
+# Avoid conflict with INSTALL_PATH set by the main Makefile
+#
+KSFT_INSTALL_PATH ?= $(BUILD)/kselftest_install
+KSFT_INSTALL_PATH := $(abspath $(KSFT_INSTALL_PATH))
+# Avoid changing the rest of the logic here and lib.mk.
+INSTALL_PATH := $(KSFT_INSTALL_PATH)
+ALL_SCRIPT := $(INSTALL_PATH)/run_kselftest.sh
+TEST_LIST := $(INSTALL_PATH)/kselftest-list.txt
+
+install: all
+ifdef INSTALL_PATH
+	@# Ask all targets to install their files
+	mkdir -p $(INSTALL_PATH)/kselftest
+	install -m 744 kselftest/module.sh $(INSTALL_PATH)/kselftest/
+	install -m 744 kselftest/runner.sh $(INSTALL_PATH)/kselftest/
+	install -m 744 kselftest/prefix.pl $(INSTALL_PATH)/kselftest/
+	install -m 744 kselftest/ktap_helpers.sh $(INSTALL_PATH)/kselftest/
+	install -m 744 kselftest/ksft.py $(INSTALL_PATH)/kselftest/
+	install -m 744 run_kselftest.sh $(INSTALL_PATH)/
+	rm -f $(TEST_LIST)
+	@ret=1;	\
+	for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET install \
+				INSTALL_PATH=$(INSTALL_PATH)/$$TARGET \
+				SRC_PATH=$(shell readlink -e $$(pwd)) \
+				OBJ_PATH=$(INSTALL_PATH) \
+				O=$(abs_objtree)		\
+				$(if $(FORCE_TARGETS),|| exit);	\
+		ret=$$((ret * $$?));		\
+	done; exit $$ret;
+
+
+	@# Ask all targets to emit their test scripts
+	@# While building kselftest-list.text skip also non-existent TARGET dirs:
+	@# they could be the result of a build failure and should NOT be
+	@# included in the generated runlist.
+	for TARGET in $(TARGETS); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		[ ! -d $(INSTALL_PATH)/$$TARGET ] && printf "Skipping non-existent dir: $$TARGET\n" && continue; \
+		printf "Emit Tests for $$TARGET\n"; \
+		$(MAKE) -s --no-print-directory OUTPUT=$$BUILD_TARGET COLLECTION=$$TARGET \
+			-C $$TARGET emit_tests >> $(TEST_LIST); \
+	done;
+	@VERSION=$$(git describe HEAD 2>/dev/null); \
+	if [ -n "$$VERSION" ]; then \
+		echo "$$VERSION" > $(INSTALL_PATH)/VERSION; \
+		printf "Version saved to $(INSTALL_PATH)/VERSION\n"; \
+	else \
+		printf "Unable to get version from git describe\n"; \
+	fi
+	@echo "**Kselftest Installation is complete: $(INSTALL_PATH)**"
+else
+	$(error Error: set INSTALL_PATH to use install)
+endif
+
+FORMAT ?= .gz
+TAR_PATH = $(abspath ${INSTALL_PATH}/kselftest-packages/kselftest.tar${FORMAT})
+gen_tar: install
+	@mkdir -p ${INSTALL_PATH}/kselftest-packages/
+	@tar caf ${TAR_PATH} --exclude=kselftest-packages -C ${INSTALL_PATH} .
+	@echo "Created ${TAR_PATH}"
+
+clean:
+	@for TARGET in $(TARGETS) $(INSTALL_DEP_TARGETS); do \
+		BUILD_TARGET=$$BUILD/$$TARGET;	\
+		$(MAKE) OUTPUT=$$BUILD_TARGET -C $$TARGET clean;\
+	done;
+
+.PHONY: all run_tests hotplug run_hotplug clean_hotplug run_pstore_crash install clean gen_tar