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, 336 insertions, 0 deletions

diff --git a/lib/Makefile b/lib/Makefile
new file mode 100644
index 000000000..7f75cc6ed
--- /dev/null
+++ b/lib/Makefile
@@ -0,0 +1,336 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for some libs needed in the kernel.
+#
+
+ccflags-remove-$(CONFIG_FUNCTION_TRACER) += $(CC_FLAGS_FTRACE)
+
+# Branch profiling isn't noinstr-safe
+ifdef CONFIG_TRACE_BRANCH_PROFILING
+CFLAGS_smp_processor_id.o += -DDISABLE_BRANCH_PROFILING
+endif
+
+# These files are disabled because they produce lots of non-interesting and/or
+# flaky coverage that is not a function of syscall inputs. For example,
+# rbtree can be global and individual rotations don't correlate with inputs.
+KCOV_INSTRUMENT_string.o := n
+KCOV_INSTRUMENT_rbtree.o := n
+KCOV_INSTRUMENT_list_debug.o := n
+KCOV_INSTRUMENT_debugobjects.o := n
+KCOV_INSTRUMENT_dynamic_debug.o := n
+KCOV_INSTRUMENT_fault-inject.o := n
+KCOV_INSTRUMENT_find_bit.o := n
+
+# string.o implements standard library functions like memset/memcpy etc.
+# Use -ffreestanding to ensure that the compiler does not try to "optimize"
+# them into calls to themselves.
+CFLAGS_string.o := -ffreestanding
+
+# Early boot use of cmdline, don't instrument it
+ifdef CONFIG_AMD_MEM_ENCRYPT
+KASAN_SANITIZE_string.o := n
+
+CFLAGS_string.o += -fno-stack-protector
+endif
+
+lib-y := ctype.o string.o vsprintf.o cmdline.o \
+	 rbtree.o radix-tree.o timerqueue.o xarray.o \
+	 maple_tree.o idr.o extable.o irq_regs.o argv_split.o \
+	 flex_proportions.o ratelimit.o \
+	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
+	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
+	 nmi_backtrace.o win_minmax.o memcat_p.o \
+	 buildid.o objpool.o iomem_copy.o sys_info.o
+
+lib-$(CONFIG_UNION_FIND) += union_find.o
+lib-$(CONFIG_PRINTK) += dump_stack.o
+lib-$(CONFIG_SMP) += cpumask.o
+lib-$(CONFIG_MIN_HEAP) += min_heap.o
+
+lib-y	+= kobject.o klist.o
+obj-y	+= lockref.o
+
+CONTEXT_ANALYSIS_rhashtable.o := y
+
+obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
+	 bust_spinlocks.o kasprintf.o bitmap.o scatterlist.o \
+	 list_sort.o uuid.o iov_iter.o clz_ctz.o \
+	 bsearch.o find_bit.o llist.o lwq.o memweight.o kfifo.o \
+	 percpu-refcount.o rhashtable.o base64.o \
+	 once.o refcount.o rcuref.o usercopy.o errseq.o bucket_locks.o \
+	 generic-radix-tree.o bitmap-str.o
+obj-y += string_helpers.o
+obj-y += hexdump.o
+obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
+obj-y += kstrtox.o
+obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
+obj-$(CONFIG_FIND_BIT_BENCHMARK_RUST) += find_bit_benchmark_rust.o
+obj-$(CONFIG_TEST_BPF) += test_bpf.o
+test_dhry-objs := dhry_1.o dhry_2.o dhry_run.o
+obj-$(CONFIG_TEST_DHRY) += test_dhry.o
+obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
+obj-$(CONFIG_TEST_BITOPS) += test_bitops.o
+CFLAGS_test_bitops.o += -Werror
+obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
+obj-$(CONFIG_TEST_IDA) += test_ida.o
+obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
+CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
+UBSAN_SANITIZE_test_ubsan.o := y
+obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
+obj-$(CONFIG_TEST_LKM) += test_module.o
+obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
+obj-$(CONFIG_TEST_WORKQUEUE) += test_workqueue.o
+obj-$(CONFIG_TEST_RHASHTABLE) += test_rhashtable.o
+obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_keys.o
+obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o
+obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o
+
+obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
+# FIXME: Clang breaks test_bitmap_const_eval when KASAN and GCOV are enabled
+GCOV_PROFILE_test_bitmap.o := n
+endif
+
+obj-$(CONFIG_TEST_XARRAY) += test_xarray.o
+obj-$(CONFIG_TEST_MAPLE_TREE) += test_maple_tree.o
+obj-$(CONFIG_TEST_PARMAN) += test_parman.o
+obj-$(CONFIG_TEST_KMOD) += test_kmod.o
+obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
+obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o
+obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
+obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
+obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o
+obj-$(CONFIG_TEST_HMM) += test_hmm.o
+obj-$(CONFIG_TEST_FREE_PAGES) += test_free_pages.o
+obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
+obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o
+obj-$(CONFIG_TEST_KEXEC_HANDOVER) += test_kho.o
+
+obj-$(CONFIG_TEST_FPU) += test_fpu.o
+test_fpu-y := test_fpu_glue.o test_fpu_impl.o
+CFLAGS_test_fpu_impl.o += $(CC_FLAGS_FPU)
+CFLAGS_REMOVE_test_fpu_impl.o += $(CC_FLAGS_NO_FPU)
+
+obj-y += kunit/
+
+ifeq ($(CONFIG_DEBUG_KOBJECT),y)
+CFLAGS_kobject.o += -DDEBUG
+CFLAGS_kobject_uevent.o += -DDEBUG
+endif
+
+obj-$(CONFIG_DEBUG_INFO_REDUCED) += debug_info.o
+CFLAGS_debug_info.o += $(call cc-option, -femit-struct-debug-detailed=any)
+
+obj-y += math/ crc/ crypto/ tests/ vdso/ raid/
+
+obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o
+obj-$(CONFIG_CHECK_SIGNATURE) += check_signature.o
+obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o
+
+obj-$(CONFIG_GENERIC_CPU_CACHE_MAINTENANCE) += cache_maint.o
+
+lib-y += logic_pio.o
+
+lib-$(CONFIG_INDIRECT_IOMEM) += logic_iomem.o
+
+obj-$(CONFIG_TRACE_MMIO_ACCESS) += trace_readwrite.o
+
+obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
+
+obj-$(CONFIG_BTREE) += btree.o
+obj-$(CONFIG_INTERVAL_TREE) += interval_tree.o
+obj-$(CONFIG_ASSOCIATIVE_ARRAY) += assoc_array.o
+obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
+obj-$(CONFIG_LIST_HARDENED) += list_debug.o
+obj-$(CONFIG_DEBUG_OBJECTS) += debugobjects.o
+
+obj-$(CONFIG_GENERIC_BITREVERSE) += bitrev.o
+obj-$(CONFIG_LINEAR_RANGES) += linear_ranges.o
+obj-$(CONFIG_PACKING)	+= packing.o
+obj-$(CONFIG_PACKING_KUNIT_TEST) += packing_test.o
+obj-$(CONFIG_XXHASH)	+= xxhash.o
+obj-$(CONFIG_GENERIC_ALLOCATOR) += genalloc.o
+
+obj-$(CONFIG_842_COMPRESS) += 842/
+obj-$(CONFIG_842_DECOMPRESS) += 842/
+obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/
+obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
+obj-$(CONFIG_ZLIB_DFLTCC) += zlib_dfltcc/
+obj-$(CONFIG_REED_SOLOMON) += reed_solomon/
+obj-$(CONFIG_BCH) += bch.o
+obj-$(CONFIG_LZO_COMPRESS) += lzo/
+obj-$(CONFIG_LZO_DECOMPRESS) += lzo/
+obj-$(CONFIG_LZ4_COMPRESS) += lz4/
+obj-$(CONFIG_LZ4HC_COMPRESS) += lz4/
+obj-$(CONFIG_LZ4_DECOMPRESS) += lz4/
+obj-$(CONFIG_ZSTD_COMPRESS) += zstd/
+obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd/
+obj-$(CONFIG_XZ_DEC) += xz/
+
+lib-$(CONFIG_DECOMPRESS_GZIP) += decompress_inflate.o
+lib-$(CONFIG_DECOMPRESS_BZIP2) += decompress_bunzip2.o
+lib-$(CONFIG_DECOMPRESS_LZMA) += decompress_unlzma.o
+lib-$(CONFIG_DECOMPRESS_XZ) += decompress_unxz.o
+lib-$(CONFIG_DECOMPRESS_LZO) += decompress_unlzo.o
+lib-$(CONFIG_DECOMPRESS_LZ4) += decompress_unlz4.o
+lib-$(CONFIG_DECOMPRESS_ZSTD) += decompress_unzstd.o
+
+obj-$(CONFIG_TEXTSEARCH) += textsearch.o
+obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o
+obj-$(CONFIG_TEXTSEARCH_BM) += ts_bm.o
+obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o
+obj-$(CONFIG_SMP) += percpu_counter.o
+obj-$(CONFIG_AUDIT_GENERIC) += audit.o
+obj-$(CONFIG_AUDIT_COMPAT_GENERIC) += compat_audit.o
+
+obj-$(CONFIG_IOMMU_HELPER) += iommu-helper.o
+obj-$(CONFIG_FAULT_INJECTION) += fault-inject.o
+obj-$(CONFIG_FAULT_INJECTION_USERCOPY) += fault-inject-usercopy.o
+obj-$(CONFIG_NOTIFIER_ERROR_INJECTION) += notifier-error-inject.o
+obj-$(CONFIG_PM_NOTIFIER_ERROR_INJECT) += pm-notifier-error-inject.o
+obj-$(CONFIG_NETDEV_NOTIFIER_ERROR_INJECT) += netdev-notifier-error-inject.o
+obj-$(CONFIG_MEMORY_NOTIFIER_ERROR_INJECT) += memory-notifier-error-inject.o
+obj-$(CONFIG_OF_RECONFIG_NOTIFIER_ERROR_INJECT) += \
+	of-reconfig-notifier-error-inject.o
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
+
+obj-$(CONFIG_CODE_TAGGING) += codetag.o
+obj-$(CONFIG_MEM_ALLOC_PROFILING) += alloc_tag.o
+
+lib-$(CONFIG_GENERIC_BUG) += bug.o
+
+obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
+obj-$(CONFIG_ARCH_NEED_CMPXCHG_1_EMU) += cmpxchg-emu.o
+
+obj-$(CONFIG_DYNAMIC_DEBUG_CORE) += dynamic_debug.o
+#ensure exported functions have prototypes
+CFLAGS_dynamic_debug.o := -DDYNAMIC_DEBUG_MODULE
+
+obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
+
+obj-$(CONFIG_NLATTR) += nlattr.o
+
+obj-$(CONFIG_LRU_CACHE) += lru_cache.o
+
+obj-$(CONFIG_GENERIC_CSUM) += checksum.o
+
+obj-$(CONFIG_GENERIC_ATOMIC64) += atomic64.o
+
+obj-$(CONFIG_ATOMIC64_SELFTEST) += atomic64_test.o
+
+obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o
+
+obj-$(CONFIG_CLOSURES) += closure.o
+
+obj-$(CONFIG_DQL) += dynamic_queue_limits.o
+
+obj-$(CONFIG_GLOB) += glob.o
+
+obj-$(CONFIG_DIMLIB) += dim/
+obj-$(CONFIG_SIGNATURE) += digsig.o
+
+lib-$(CONFIG_CLZ_TAB) += clz_tab.o
+
+obj-$(CONFIG_GENERIC_STRNCPY_FROM_USER) += strncpy_from_user.o
+obj-$(CONFIG_GENERIC_STRNLEN_USER) += strnlen_user.o
+
+obj-$(CONFIG_GENERIC_NET_UTILS) += net_utils.o
+
+obj-$(CONFIG_SG_SPLIT) += sg_split.o
+obj-$(CONFIG_SG_POOL) += sg_pool.o
+obj-$(CONFIG_MEMREGION) += memregion.o
+obj-$(CONFIG_STMP_DEVICE) += stmp_device.o
+obj-$(CONFIG_IRQ_POLL) += irq_poll.o
+
+# stackdepot.c should not be instrumented or call instrumented functions.
+# Prevent the compiler from calling builtins like memcmp() or bcmp() from this
+# file.
+CFLAGS_stackdepot.o += -fno-builtin
+CONTEXT_ANALYSIS_stackdepot.o := y
+obj-$(CONFIG_STACKDEPOT) += stackdepot.o
+KASAN_SANITIZE_stackdepot.o := n
+# In particular, instrumenting stackdepot.c with KMSAN will result in infinite
+# recursion.
+KMSAN_SANITIZE_stackdepot.o := n
+KCOV_INSTRUMENT_stackdepot.o := n
+
+obj-$(CONFIG_REF_TRACKER) += ref_tracker.o
+
+libfdt_files = fdt.o fdt_ro.o fdt_wip.o fdt_rw.o fdt_sw.o fdt_strerror.o \
+	       fdt_empty_tree.o fdt_addresses.o
+$(foreach file, $(libfdt_files), \
+	$(eval CFLAGS_$(file) = -I $(srctree)/scripts/dtc/libfdt))
+lib-$(CONFIG_LIBFDT) += $(libfdt_files)
+
+obj-$(CONFIG_BOOT_CONFIG) += bootconfig.o
+obj-$(CONFIG_BOOT_CONFIG_EMBED) += bootconfig-data.o
+
+$(obj)/bootconfig-data.o: $(obj)/default.bconf
+
+targets += default.bconf
+filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
+$(obj)/default.bconf: $(CONFIG_BOOT_CONFIG_EMBED_FILE) FORCE
+	$(call filechk,defbconf)
+
+obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
+obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
+
+obj-$(CONFIG_PERCPU_TEST) += percpu_test.o
+
+obj-$(CONFIG_ASN1) += asn1_decoder.o
+obj-$(CONFIG_ASN1_ENCODER) += asn1_encoder.o
+
+obj-$(CONFIG_FONT_SUPPORT) += fonts/
+
+#
+# Build a fast OID lookip registry from include/linux/oid_registry.h
+#
+obj-$(CONFIG_OID_REGISTRY) += oid_registry.o
+
+$(obj)/oid_registry.o: $(obj)/oid_registry_data.c
+
+$(obj)/oid_registry_data.c: $(srctree)/include/linux/oid_registry.h \
+			    $(src)/build_OID_registry
+	$(call cmd,build_OID_registry)
+
+quiet_cmd_build_OID_registry = GEN     $@
+      cmd_build_OID_registry = perl $(src)/build_OID_registry $< $@
+
+clean-files	+= oid_registry_data.c
+
+obj-$(CONFIG_UCS2_STRING) += ucs2_string.o
+obj-$(CONFIG_UBSAN) += ubsan.o
+
+UBSAN_SANITIZE_ubsan.o := n
+KASAN_SANITIZE_ubsan.o := n
+KCSAN_SANITIZE_ubsan.o := n
+KMSAN_SANITIZE_ubsan.o := n
+CFLAGS_ubsan.o := -fno-stack-protector $(DISABLE_KSTACK_ERASE)
+
+obj-$(CONFIG_SBITMAP) += sbitmap.o
+
+obj-$(CONFIG_PARMAN) += parman.o
+
+obj-y += group_cpus.o
+
+# GCC library routines
+obj-$(CONFIG_GENERIC_LIB_ASHLDI3) += ashldi3.o
+obj-$(CONFIG_GENERIC_LIB_ASHRDI3) += ashrdi3.o
+obj-$(CONFIG_GENERIC_LIB_LSHRDI3) += lshrdi3.o
+obj-$(CONFIG_GENERIC_LIB_MULDI3) += muldi3.o
+obj-$(CONFIG_GENERIC_LIB_CMPDI2) += cmpdi2.o
+obj-$(CONFIG_GENERIC_LIB_UCMPDI2) += ucmpdi2.o
+obj-$(CONFIG_OBJAGG) += objagg.o
+
+# pldmfw library
+obj-$(CONFIG_PLDMFW) += pldmfw/
+
+obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
+
+obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
+
+CONTEXT_ANALYSIS_test_context-analysis.o := y
+obj-$(CONFIG_CONTEXT_ANALYSIS_TEST) += test_context-analysis.o
+
+subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify