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, 57 insertions, 0 deletions

diff --git a/arch/arm/tools/Makefile b/arch/arm/tools/Makefile
new file mode 100644
index 000000000..28b6da8ac
--- /dev/null
+++ b/arch/arm/tools/Makefile
@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# linux/arch/arm/tools/Makefile
+#
+# Copyright (C) 2001 Russell King
+#
+
+gen := arch/$(ARCH)/include/generated
+kapi := $(gen)/asm
+uapi := $(gen)/uapi/asm
+syshdr := $(srctree)/scripts/syscallhdr.sh
+sysnr := $(src)/syscallnr.sh
+systbl := $(srctree)/scripts/syscalltbl.sh
+syscall := $(src)/syscall.tbl
+
+gen-y := $(gen)/calls-oabi.S
+gen-y += $(gen)/calls-eabi.S
+kapi-hdrs-y := $(kapi)/unistd-nr.h
+kapi-hdrs-y += $(kapi)/mach-types.h
+uapi-hdrs-y += $(uapi)/unistd-oabi.h
+uapi-hdrs-y += $(uapi)/unistd-eabi.h
+
+targets += $(addprefix ../../../,$(gen-y) $(kapi-hdrs-y) $(uapi-hdrs-y))
+
+PHONY += kapi uapi
+
+kapi:	$(kapi-hdrs-y) $(gen-y)
+
+uapi:	$(uapi-hdrs-y)
+
+# Create output directory if not already present
+$(shell mkdir -p $(kapi) $(uapi))
+
+quiet_cmd_gen_mach = GEN     $@
+      cmd_gen_mach = $(AWK) -f $(real-prereqs) > $@
+
+$(kapi)/mach-types.h: $(src)/gen-mach-types $(src)/mach-types FORCE
+	$(call if_changed,gen_mach)
+
+quiet_cmd_syshdr = SYSHDR  $@
+      cmd_syshdr = $(CONFIG_SHELL) $(syshdr) --abis common,$* \
+		   --offset __NR_SYSCALL_BASE $< $@
+
+quiet_cmd_systbl = SYSTBL  $@
+      cmd_systbl = $(CONFIG_SHELL) $(systbl) --abis common,$* $< $@
+
+quiet_cmd_sysnr  = SYSNR   $@
+      cmd_sysnr  = $(CONFIG_SHELL) $(sysnr) $< $@
+
+$(uapi)/unistd-%.h: $(syscall) $(syshdr) FORCE
+	$(call if_changed,syshdr)
+
+$(kapi)/unistd-nr.h: $(syscall) $(sysnr) FORCE
+	$(call if_changed,sysnr)
+
+$(gen)/calls-%.S: $(syscall) $(systbl) FORCE
+	$(call if_changed,systbl)