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, 105 insertions, 0 deletions

diff --git a/scripts/Makefile.asm-headers b/scripts/Makefile.asm-headers
new file mode 100644
index 000000000..f1c3d287c
--- /dev/null
+++ b/scripts/Makefile.asm-headers
@@ -0,0 +1,105 @@
+# SPDX-License-Identifier: GPL-2.0
+# include/asm-generic contains a lot of files that are used
+# verbatim by several architectures.
+#
+# This Makefile generates arch/$(SRCARCH)/include/generated/(uapi/)/asm
+# headers from multiple sources:
+#  - a small wrapper to include the corresponding asm-generic/*.h
+#    is generated for each file listed as generic-y
+#  - uapi/asm/unistd_*.h files listed as syscalls-y are generated from
+#    syscall.tbl with the __NR_* macros
+#  - Corresponding asm/syscall_table_*.h are generated from the same input
+
+PHONY := all
+all:
+
+src := $(srctree)/$(subst /generated,,$(obj))
+
+syscall_abis_32  += common,32
+syscall_abis_64  += common,64
+syscalltbl := $(srctree)/scripts/syscall.tbl
+syshdr-args := --emit-nr
+
+# let architectures override $(syscall_abis_%) and $(syscalltbl)
+-include $(srctree)/arch/$(SRCARCH)/kernel/Makefile.syscalls
+include $(srctree)/scripts/Kbuild.include
+-include $(kbuild-file)
+
+syshdr := $(srctree)/scripts/syscallhdr.sh
+systbl := $(srctree)/scripts/syscalltbl.sh
+
+# $(generic)/Kbuild lists mandatory-y. Exclude um since it is a special case.
+ifneq ($(SRCARCH),um)
+include $(srctree)/$(generic)/Kbuild
+endif
+
+redundant := $(filter $(mandatory-y) $(generated-y), $(generic-y))
+redundant += $(foreach f, $(generic-y), $(if $(wildcard $(src)/$(f)),$(f)))
+redundant := $(sort $(redundant))
+$(if $(redundant),\
+	$(warning redundant generic-y found in $(src)/Kbuild: $(redundant)))
+
+# If arch does not implement mandatory headers, fallback to asm-generic ones.
+mandatory-y := $(filter-out $(generated-y), $(mandatory-y))
+generic-y   += $(foreach f, $(mandatory-y), $(if $(wildcard $(src)/$(f)),,$(f)))
+
+generic-y   := $(addprefix $(obj)/, $(generic-y))
+syscall-y   := $(addprefix $(obj)/, $(syscall-y))
+generated-y := $(addprefix $(obj)/, $(generated-y))
+
+# Remove stale wrappers when the corresponding files are removed from generic-y
+old-headers := $(shell test -d $(obj) && find $(obj) -name '*.h' ! -name '.*')
+unwanted    := $(filter-out $(generic-y) $(generated-y) $(syscall-y),$(old-headers))
+
+filechk_wrap = echo "\#include <asm-generic/$*.h>"
+
+quiet_cmd_remove = REMOVE  $(unwanted)
+      cmd_remove = rm -f $(unwanted); find $(obj) -type d -empty -delete
+
+quiet_cmd_syshdr = SYSHDR  $@
+      cmd_syshdr = $(CONFIG_SHELL) $(syshdr) \
+		   $(if $(syshdr-args-$*),$(syshdr-args-$*),$(syshdr-args)) \
+		   $(if $(syscall_compat),--prefix "compat$*_") \
+		   --abis $(subst $(space),$(comma),$(strip $(syscall_abis_$*))) \
+		   $< $@
+
+quiet_cmd_systbl = SYSTBL  $@
+      cmd_systbl = $(CONFIG_SHELL) $(systbl) \
+		   $(if $(systbl-args-$*),$(systbl-args-$*),$(systbl-args)) \
+		   --abis $(subst $(space),$(comma),$(strip $(syscall_abis_$*))) \
+		   $< $@
+
+all: $(generic-y) $(syscall-y)
+	$(if $(unwanted),$(call cmd,remove))
+	@:
+
+$(obj)/%.h: $(srctree)/$(generic)/%.h FORCE
+	$(call filechk,wrap)
+
+$(obj)/unistd_%.h: $(syscalltbl) $(syshdr) FORCE
+	$(call if_changed,syshdr)
+
+$(obj)/unistd_compat_%.h: syscall_compat:=1
+$(obj)/unistd_compat_%.h: $(syscalltbl) $(syshdr) FORCE
+	$(call if_changed,syshdr)
+
+$(obj)/syscall_table_%.h: $(syscalltbl) $(systbl) FORCE
+	$(call if_changed,systbl)
+
+targets := $(syscall-y)
+
+# Create output directory. Skip it if at least one old header exists
+# since we know the output directory already exists.
+ifeq ($(old-headers),)
+$(shell mkdir -p $(obj))
+endif
+
+PHONY += FORCE
+
+FORCE:
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)