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, 75 insertions, 0 deletions

diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
new file mode 100644
index 000000000..b1b7a1419
--- /dev/null
+++ b/arch/powerpc/lib/Makefile
@@ -0,0 +1,75 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for ppc-specific library files..
+#
+
+CFLAGS_code-patching.o += -fno-stack-protector
+CFLAGS_feature-fixups.o += -fno-stack-protector
+
+CFLAGS_REMOVE_code-patching.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_feature-fixups.o = $(CC_FLAGS_FTRACE)
+
+KASAN_SANITIZE_code-patching.o := n
+KASAN_SANITIZE_feature-fixups.o := n
+# restart_table.o contains functions called in the NMI interrupt path
+# which can be in real mode. Disable KASAN.
+KASAN_SANITIZE_restart_table.o := n
+KCSAN_SANITIZE_code-patching.o := n
+KCSAN_SANITIZE_feature-fixups.o := n
+
+ifdef CONFIG_KASAN
+CFLAGS_code-patching.o += -DDISABLE_BRANCH_PROFILING
+CFLAGS_feature-fixups.o += -DDISABLE_BRANCH_PROFILING
+endif
+
+CFLAGS_code-patching.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+CFLAGS_feature-fixups.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+
+obj-y += code-patching.o feature-fixups.o pmem.o
+
+obj-$(CONFIG_CODE_PATCHING_SELFTEST) += test-code-patching.o
+
+ifndef CONFIG_KASAN
+obj-y	+=	string.o memcmp_$(BITS).o
+obj-$(CONFIG_PPC32)	+= strlen_32.o
+endif
+
+obj-$(CONFIG_PPC32)	+= div64.o copy_32.o crtsavres.o
+
+obj-$(CONFIG_FUNCTION_ERROR_INJECTION)	+= error-inject.o
+
+# See corresponding test in arch/powerpc/Makefile
+# 64-bit linker creates .sfpr on demand for final link (vmlinux),
+# so it is only needed for modules, and only for older linkers which
+# do not support --save-restore-funcs
+ifndef CONFIG_LD_IS_BFD
+always-$(CONFIG_PPC64)	+= crtsavres.o
+endif
+
+obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
+			       memcpy_power7.o restart_table.o
+
+obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
+	   memcpy_64.o copy_mc_64.o
+
+ifdef CONFIG_PPC_QUEUED_SPINLOCKS
+obj-$(CONFIG_SMP)	+= qspinlock.o
+else
+obj64-$(CONFIG_SMP)	+= locks.o
+endif
+
+obj64-$(CONFIG_ALTIVEC)	+= vmx-helper.o
+obj64-$(CONFIG_KPROBES_SANITY_TEST)	+= test_emulate_step.o \
+					   test_emulate_step_exec_instr.o
+
+obj-y			+= checksum_$(BITS).o string_$(BITS).o
+
+obj-y			+= sstep.o
+obj-$(CONFIG_PPC_FPU)	+= ldstfp.o
+obj64-y			+= quad.o
+
+obj-$(CONFIG_PPC_LIB_RHEAP) += rheap.o
+
+obj-$(CONFIG_FTR_FIXUP_SELFTEST) += feature-fixups-test.o
+
+obj-$(CONFIG_PPC64) += $(obj64-y)