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, 127 insertions, 0 deletions

diff --git a/arch/mips/generic/Kconfig b/arch/mips/generic/Kconfig
new file mode 100644
index 000000000..7dc5b3821
--- /dev/null
+++ b/arch/mips/generic/Kconfig
@@ -0,0 +1,127 @@
+# SPDX-License-Identifier: GPL-2.0
+if MIPS_GENERIC_KERNEL
+
+config LEGACY_BOARDS
+	bool
+	help
+	  Select this from your board if the board must use a legacy, non-UHI,
+	  boot protocol. This will cause the kernel to scan through the list of
+	  supported machines calling their detect functions in turn if the
+	  kernel is booted without being provided with an FDT via the UHI
+	  boot protocol.
+
+config YAMON_DT_SHIM
+	bool
+	help
+	  Select this from your board if the board uses the YAMON bootloader
+	  and you wish to include code which helps translate various
+	  YAMON-provided environment variables into a device tree properties.
+
+comment "Legacy (non-UHI/non-FIT) Boards"
+
+config LEGACY_BOARD_SEAD3
+	bool "Support MIPS SEAD-3 boards"
+	select LEGACY_BOARDS
+	select YAMON_DT_SHIM
+	help
+	  Enable this to include support for booting on MIPS SEAD-3 FPGA-based
+	  development boards, which boot using a legacy boot protocol.
+
+comment "MSCC Ocelot doesn't work with SEAD3 enabled"
+	depends on LEGACY_BOARD_SEAD3
+
+config LEGACY_BOARD_OCELOT
+	bool "Legacy support for Ocelot based boards"
+	depends on LEGACY_BOARD_SEAD3=n
+	select LEGACY_BOARDS
+	select SOC_VCOREIII
+	select SYS_HAS_EARLY_PRINTK
+	select USE_GENERIC_EARLY_PRINTK_8250
+
+config SOC_VCOREIII
+	bool
+	select GPIOLIB
+	select MSCC_OCELOT_IRQ
+	select MSCC_OCELOT #will be removed when driver no more use it
+
+#Will be removed when the driver using it will be converted to SOC_VCOREIII
+config MSCC_OCELOT
+	bool
+
+comment "FIT/UHI Boards"
+
+config FIT_IMAGE_FDT_BOSTON
+	bool "Include FDT for MIPS Boston boards"
+	help
+	  Enable this to include the FDT for the MIPS Boston development board
+	  from Imagination Technologies in the FIT kernel image. You should
+	  enable this if you wish to boot on a MIPS Boston board, as it is
+	  expected by the bootloader.
+
+config FIT_IMAGE_FDT_MARDUK
+	bool "Include FDT for IMG Pistachio Marduk (CI40) boards"
+	help
+	  Enable this to include the FDT for the IMG Pistachio Marduk (CI40)
+	  from Imagination Technologies in the FIT kernel image.
+
+config FIT_IMAGE_FDT_NI169445
+	bool "Include FDT for NI 169445"
+	help
+	  Enable this to include the FDT for the 169445 platform from
+	  National Instruments in the FIT kernel image.
+
+config FIT_IMAGE_FDT_XILFPGA
+	bool "Include FDT for Xilfpga"
+	help
+	  Enable this to include the FDT for the MIPSfpga platform
+	  from Imagination Technologies in the FIT kernel image.
+
+config FIT_IMAGE_FDT_OCELOT
+	bool "Include FDT for Microsemi Ocelot development platforms"
+	select SOC_VCOREIII
+	help
+	  Enable this to include the FDT for the Ocelot development platforms
+	  from Microsemi in the FIT kernel image.
+	  This requires u-boot on the platform.
+
+config FIT_IMAGE_FDT_LUTON
+	bool "Include FDT for Microsemi Luton development platforms"
+	select SOC_VCOREIII
+	help
+	  Enable this to include the FDT for the Luton development platforms
+	  from Microsemi in the FIT kernel image.
+	  This requires u-boot on the platform.
+
+config FIT_IMAGE_FDT_JAGUAR2
+	bool "Include FDT for Microsemi Jaguar2 development platforms"
+	select SOC_VCOREIII
+	help
+	  Enable this to include the FDT for the Jaguar2 development platforms
+	  from Microsemi in the FIT kernel image.
+	  This requires u-boot on the platform.
+
+config FIT_IMAGE_FDT_SERVAL
+	bool "Include FDT for Microsemi Serval development platforms"
+	select SOC_VCOREIII
+	help
+	  Enable this to include the FDT for the Serval development platforms
+	  from Microsemi in the FIT kernel image.
+	  This requires u-boot on the platform.
+
+config BOARD_INGENIC
+	bool "Support boards based on Ingenic SoCs"
+	select MACH_INGENIC_GENERIC
+	help
+	  Enable support for boards based on Ingenic SoCs.
+
+config VIRT_BOARD_RANCHU
+	bool "Support Ranchu platform for Android emulator"
+	help
+	  This enables support for the platform used by Android emulator.
+
+	  Ranchu platform consists of a set of virtual devices. This platform
+	  enables emulation of variety of virtual configurations while using
+	  Android emulator. Android emulator is based on Qemu, and contains
+	  the support for the same set of virtual devices.
+
+endif