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, 176 insertions, 0 deletions

diff --git a/arch/mips/boot/Makefile b/arch/mips/boot/Makefile
new file mode 100644
index 000000000..8473c4671
--- /dev/null
+++ b/arch/mips/boot/Makefile
@@ -0,0 +1,176 @@
+#
+# 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) 1995, 1998, 2001, 2002 by Ralf Baechle
+# Copyright (C) 2004  Maciej W. Rozycki
+#
+
+#
+# Some DECstations need all possible sections of an ECOFF executable
+#
+ifdef CONFIG_MACH_DECSTATION
+  e2eflag := -a
+endif
+
+#
+# Drop some uninteresting sections in the kernel.
+# This is only relevant for ELF kernels but doesn't hurt a.out
+#
+drop-sections := .reginfo .mdebug .comment .note .pdr .options .MIPS.options
+strip-flags   := $(addprefix --remove-section=,$(drop-sections))
+
+hostprogs := elf2ecoff
+
+suffix-y			:= bin
+suffix-$(CONFIG_KERNEL_BZIP2)	:= bz2
+suffix-$(CONFIG_KERNEL_GZIP)	:= gz
+suffix-$(CONFIG_KERNEL_LZMA)	:= lzma
+suffix-$(CONFIG_KERNEL_LZO)	:= lzo
+
+targets := vmlinux.ecoff
+quiet_cmd_ecoff = ECOFF	  $@
+      cmd_ecoff = $(obj)/elf2ecoff $(VMLINUX) $@ $(e2eflag)
+$(obj)/vmlinux.ecoff: $(obj)/elf2ecoff $(VMLINUX) FORCE
+	$(call if_changed,ecoff)
+
+targets += vmlinux.bin
+quiet_cmd_bin = OBJCOPY $@
+      cmd_bin = $(OBJCOPY) -O binary $(strip-flags) $(VMLINUX) $@
+$(obj)/vmlinux.bin: $(VMLINUX) FORCE
+	$(call if_changed,bin)
+
+targets += vmlinux.srec
+quiet_cmd_srec = OBJCOPY $@
+      cmd_srec = $(OBJCOPY) -S -O srec $(strip-flags) $(VMLINUX) $@
+$(obj)/vmlinux.srec: $(VMLINUX) FORCE
+	$(call if_changed,srec)
+
+UIMAGE_LOADADDR  = $(VMLINUX_LOAD_ADDRESS)
+UIMAGE_ENTRYADDR = $(VMLINUX_ENTRY_ADDRESS)
+
+#
+# Compressed vmlinux images
+#
+
+targets += vmlinux.bin.bz2
+targets += vmlinux.bin.gz
+targets += vmlinux.bin.lzma
+targets += vmlinux.bin.lzo
+
+$(obj)/vmlinux.bin.bz2: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,bzip2)
+
+$(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,gzip)
+
+$(obj)/vmlinux.bin.lzma: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,lzma)
+
+$(obj)/vmlinux.bin.lzo: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,lzo)
+
+#
+# Compressed u-boot images
+#
+
+targets += uImage
+targets += uImage.bin
+targets += uImage.bz2
+targets += uImage.gz
+targets += uImage.lzma
+targets += uImage.lzo
+
+$(obj)/uImage.bin: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,uimage,none)
+
+$(obj)/uImage.bz2: $(obj)/vmlinux.bin.bz2 FORCE
+	$(call if_changed,uimage,bzip2)
+
+$(obj)/uImage.gz: $(obj)/vmlinux.bin.gz FORCE
+	$(call if_changed,uimage,gzip)
+
+$(obj)/uImage.lzma: $(obj)/vmlinux.bin.lzma FORCE
+	$(call if_changed,uimage,lzma)
+
+$(obj)/uImage.lzo: $(obj)/vmlinux.bin.lzo FORCE
+	$(call if_changed,uimage,lzo)
+
+$(obj)/uImage: $(obj)/uImage.$(suffix-y)
+	@ln -sf $(notdir $<) $@
+	@echo '  Image $@ is ready'
+
+#
+# Flattened Image Tree (.itb) images
+#
+
+ifeq ($(ADDR_BITS),32)
+itb_addr_cells = 1
+endif
+ifeq ($(ADDR_BITS),64)
+itb_addr_cells = 2
+endif
+
+targets += vmlinux.its.S
+
+quiet_cmd_its_cat = CAT     $@
+      cmd_its_cat = cat $(real-prereqs) >$@
+
+$(obj)/vmlinux.its.S: $(addprefix $(srctree)/arch/mips/$(PLATFORM)/,$(ITS_INPUTS)) FORCE
+	$(call if_changed,its_cat)
+
+targets += vmlinux.its
+targets += vmlinux.gz.its
+targets += vmlinux.bz2.its
+targets += vmlinux.lzma.its
+targets += vmlinux.lzo.its
+
+quiet_cmd_cpp_its_S = ITS     $@
+      cmd_cpp_its_S = $(CPP) -P -C -o $@ $< \
+		        -DKERNEL_NAME="\"Linux $(KERNELRELEASE)\"" \
+			-DVMLINUX_BINARY="\"$(3)\"" \
+			-DVMLINUX_COMPRESSION="\"$(2)\"" \
+			-DVMLINUX_LOAD_ADDRESS=$(VMLINUX_LOAD_ADDRESS) \
+			-DVMLINUX_ENTRY_ADDRESS=$(VMLINUX_ENTRY_ADDRESS) \
+			-DADDR_BITS=$(ADDR_BITS) \
+			-DADDR_CELLS=$(itb_addr_cells)
+
+$(obj)/vmlinux.its: $(obj)/vmlinux.its.S $(VMLINUX) FORCE
+	$(call if_changed,cpp_its_S,none,vmlinux.bin)
+
+$(obj)/vmlinux.gz.its: $(obj)/vmlinux.its.S $(VMLINUX) FORCE
+	$(call if_changed,cpp_its_S,gzip,vmlinux.bin.gz)
+
+$(obj)/vmlinux.bz2.its: $(obj)/vmlinux.its.S $(VMLINUX)  FORCE
+	$(call if_changed,cpp_its_S,bzip2,vmlinux.bin.bz2)
+
+$(obj)/vmlinux.lzma.its: $(obj)/vmlinux.its.S $(VMLINUX) FORCE
+	$(call if_changed,cpp_its_S,lzma,vmlinux.bin.lzma)
+
+$(obj)/vmlinux.lzo.its: $(obj)/vmlinux.its.S $(VMLINUX) FORCE
+	$(call if_changed,cpp_its_S,lzo,vmlinux.bin.lzo)
+
+targets += vmlinux.itb
+targets += vmlinux.gz.itb
+targets += vmlinux.bz2.itb
+targets += vmlinux.lzma.itb
+targets += vmlinux.lzo.itb
+
+quiet_cmd_itb-image = ITB     $@
+      cmd_itb-image = \
+		env PATH="$(objtree)/scripts/dtc:$(PATH)" \
+		$(BASH) $(MKIMAGE) \
+		-D "-I dts -O dtb -p 500 \
+			--include $(objtree)/arch/mips \
+			--warning no-unit_address_vs_reg" \
+		-f $(2) $@
+
+$(obj)/vmlinux.itb: $(obj)/vmlinux.its $(obj)/vmlinux.bin FORCE
+	$(call if_changed,itb-image,$<)
+
+$(obj)/vmlinux.%.itb: $(obj)/vmlinux.%.its $(obj)/vmlinux.bin.% FORCE
+	$(call if_changed,itb-image,$<)
+
+# for cleaning
+subdir- += compressed tools