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, 120 insertions, 0 deletions

diff --git a/arch/alpha/boot/Makefile b/arch/alpha/boot/Makefile
new file mode 100644
index 000000000..d8dba85e6
--- /dev/null
+++ b/arch/alpha/boot/Makefile
@@ -0,0 +1,120 @@
+#
+# arch/alpha/boot/Makefile
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1994 by Linus Torvalds
+#
+
+hostprogs	:= tools/mkbb tools/objstrip
+targets		:= vmlinux.gz vmlinux \
+		   vmlinux.nh tools/lxboot tools/bootlx tools/bootph \
+		   tools/bootpzh bootloader bootpheader bootpzheader 
+OBJSTRIP	:= $(obj)/tools/objstrip
+
+KBUILD_HOSTCFLAGS := -Wall -I$(objtree)/usr/include
+BOOTCFLAGS	+= -I$(objtree)/$(obj) -I$(srctree)/$(obj)
+
+# SRM bootable image.  Copy to offset 512 of a partition.
+$(obj)/bootimage: $(addprefix $(obj)/tools/,mkbb lxboot bootlx) $(obj)/vmlinux.nh
+	( cat $(obj)/tools/lxboot $(obj)/tools/bootlx $(obj)/vmlinux.nh ) > $@ 
+	$(obj)/tools/mkbb $@ $(obj)/tools/lxboot
+	@echo '  Bootimage $@ is ready'
+
+# BOOTP bootable image.  Define INITRD during make to append initrd image.
+$(obj)/bootpfile: $(obj)/tools/bootph $(obj)/vmlinux.nh
+	cat $(obj)/tools/bootph $(obj)/vmlinux.nh > $@
+ifdef INITRD
+	cat $(INITRD) >> $@
+endif
+
+# Compressed kernel BOOTP bootable image.
+# Define INITRD during make to append initrd image.
+$(obj)/bootpzfile: $(obj)/tools/bootpzh $(obj)/vmlinux.nh.gz
+	cat $(obj)/tools/bootpzh $(obj)/vmlinux.nh.gz > $@
+ifdef INITRD
+	cat $(INITRD) >> $@
+endif
+
+# Compressed kernel image
+$(obj)/vmlinux.gz: $(obj)/vmlinux FORCE
+	$(call if_changed,gzip)
+	@echo '  Kernel $@ is ready'
+
+$(obj)/main.o: $(obj)/ksize.h
+$(obj)/bootp.o: $(obj)/ksize.h
+$(obj)/bootpz.o: $(obj)/kzsize.h
+
+$(obj)/ksize.h: $(obj)/vmlinux.nh FORCE
+	echo "#define KERNEL_SIZE `ls -l $(obj)/vmlinux.nh | awk '{print $$5}'`" > $@T
+ifdef INITRD
+	[ -f $(INITRD) ] || exit 1
+	echo "#define INITRD_IMAGE_SIZE `ls -l $(INITRD) | awk '{print $$5}'`" >> $@T
+endif
+	cmp -s $@T $@ || mv -f $@T $@
+	rm -f $@T
+
+$(obj)/kzsize.h: $(obj)/vmlinux.nh.gz FORCE
+	echo "#define KERNEL_SIZE `ls -l $(obj)/vmlinux.nh | awk '{print $$5}'`" > $@T
+	echo "#define KERNEL_Z_SIZE `ls -l $(obj)/vmlinux.nh.gz | awk '{print $$5}'`" >> $@T
+ifdef INITRD
+	[ -f $(INITRD) ] || exit 1
+	echo "#define INITRD_IMAGE_SIZE `ls -l $(INITRD) | awk '{print $$5}'`" >> $@T
+endif
+	cmp -s $@T $@ || mv -f $@T $@
+	rm -f $@T
+
+quiet_cmd_strip = STRIP  $@
+      cmd_strip = $(STRIP) -o $@ $<
+
+$(obj)/vmlinux: vmlinux FORCE
+	$(call if_changed,strip)
+
+quiet_cmd_objstrip = OBJSTRIP $@
+      cmd_objstrip = $(OBJSTRIP) $(OSFLAGS_$(@F)) $< $@
+
+OSFLAGS_vmlinux.nh	:= -v
+OSFLAGS_lxboot		:= -p
+OSFLAGS_bootlx		:= -vb
+OSFLAGS_bootph		:= -vb
+OSFLAGS_bootpzh		:= -vb
+
+$(obj)/vmlinux.nh: vmlinux $(OBJSTRIP) FORCE
+	$(call if_changed,objstrip)
+
+$(obj)/vmlinux.nh.gz: $(obj)/vmlinux.nh FORCE
+	$(call if_changed,gzip)
+
+$(obj)/tools/lxboot: $(obj)/bootloader $(OBJSTRIP) FORCE
+	$(call if_changed,objstrip)
+
+$(obj)/tools/bootlx: $(obj)/bootloader $(OBJSTRIP) FORCE
+	$(call if_changed,objstrip)
+
+$(obj)/tools/bootph: $(obj)/bootpheader $(OBJSTRIP) FORCE
+	$(call if_changed,objstrip)
+
+$(obj)/tools/bootpzh: $(obj)/bootpzheader $(OBJSTRIP) FORCE
+	$(call if_changed,objstrip)
+
+LDFLAGS_bootloader   := -static -T # -N -relax
+LDFLAGS_bootloader   := -static -T # -N -relax
+LDFLAGS_bootpheader  := -static -T # -N -relax
+LDFLAGS_bootpzheader := -static -T # -N -relax
+
+OBJ_bootlx   := $(obj)/head.o $(obj)/stdio.o $(obj)/main.o
+OBJ_bootph   := $(obj)/head.o $(obj)/stdio.o $(obj)/bootp.o
+OBJ_bootpzh  := $(obj)/head.o $(obj)/stdio.o $(obj)/bootpz.o $(obj)/misc.o
+
+$(obj)/bootloader: $(obj)/bootloader.lds $(OBJ_bootlx) $(LIBS_Y) FORCE
+	$(call if_changed,ld)
+
+$(obj)/bootpheader: $(obj)/bootloader.lds $(OBJ_bootph) $(LIBS_Y) FORCE
+	$(call if_changed,ld)
+
+$(obj)/bootpzheader: $(obj)/bootloader.lds $(OBJ_bootpzh) $(LIBS_Y) FORCE
+	$(call if_changed,ld)
+
+$(obj)/misc.o: lib/inflate.c