sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 69 insertions, 0 deletions

diff --git a/scripts/Makefile b/scripts/Makefile
new file mode 100644
index 000000000..3434a82a1
--- /dev/null
+++ b/scripts/Makefile
@@ -0,0 +1,69 @@
+# SPDX-License-Identifier: GPL-2.0
+###
+# scripts contains sources for various helper programs used throughout
+# the kernel for the build process.
+
+hostprogs-always-$(CONFIG_KALLSYMS)			+= kallsyms
+hostprogs-always-$(BUILD_C_RECORDMCOUNT)		+= recordmcount
+hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT)		+= sorttable
+hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
+hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
+hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
+hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_builder
+hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_gen
+hostprogs-always-$(CONFIG_TRACEPOINTS)			+= tracepoint-update
+
+sorttable-objs := sorttable.o elf-parse.o
+tracepoint-update-objs := tracepoint-update.o elf-parse.o
+
+ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
+always-$(CONFIG_RUST)					+= target.json
+filechk_rust_target = $< < include/config/auto.conf
+
+$(obj)/target.json: scripts/generate_rust_target include/config/auto.conf FORCE
+	$(call filechk,rust_target)
+endif
+
+hostprogs += generate_rust_target
+generate_rust_target-rust := y
+rustdoc_test_builder-rust := y
+rustdoc_test_gen-rust := y
+
+HOSTCFLAGS_tracepoint-update.o = -I$(srctree)/tools/include
+HOSTCFLAGS_elf-parse.o = -I$(srctree)/tools/include
+HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
+HOSTLDLIBS_sorttable = -lpthread
+HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
+HOSTCFLAGS_sign-file.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)
+HOSTCFLAGS_sign-file.o += -I$(srctree)/tools/include/uapi/
+HOSTLDLIBS_sign-file = $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)
+
+ifdef CONFIG_UNWINDER_ORC
+ifeq ($(ARCH),x86_64)
+SRCARCH := x86
+endif
+ifeq ($(ARCH),loongarch)
+SRCARCH := loongarch
+endif
+HOSTCFLAGS_sorttable.o += -I$(srctree)/tools/arch/$(SRCARCH)/include
+HOSTCFLAGS_sorttable.o += -DUNWINDER_ORC_ENABLED
+endif
+
+ifdef CONFIG_BUILDTIME_MCOUNT_SORT
+HOSTCFLAGS_sorttable.o += -DMCOUNT_SORT_ENABLED
+endif
+
+# The following programs are only built on demand
+hostprogs += unifdef gen_packed_field_checks
+
+# The module linker script is preprocessed on demand
+targets += module.lds
+
+subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
+subdir-$(CONFIG_GENKSYMS) += genksyms
+subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
+subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+subdir-$(CONFIG_SECURITY_IPE) += ipe
+
+# Let clean descend into subdirs
+subdir-	+= basic dtc gdb kconfig mod