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, 262 insertions, 0 deletions

diff --git a/drivers/net/wan/Kconfig b/drivers/net/wan/Kconfig
new file mode 100644
index 000000000..67be9857c
--- /dev/null
+++ b/drivers/net/wan/Kconfig
@@ -0,0 +1,262 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# wan devices configuration
+#
+
+menuconfig WAN
+	bool "Wan interfaces support"
+	help
+	  Wide Area Networks (WANs), such as X.25, Frame Relay and leased
+	  lines, are used to interconnect Local Area Networks (LANs) over vast
+	  distances with data transfer rates significantly higher than those
+	  achievable with commonly used asynchronous modem connections.
+
+	  Usually, a quite expensive external device called a `WAN router' is
+	  needed to connect to a WAN. As an alternative, a relatively
+	  inexpensive WAN interface card can allow your Linux box to directly
+	  connect to a WAN.
+
+	  If you have one of those cards and wish to use it under Linux,
+	  say Y here and also to the WAN driver for your card.
+
+	  If unsure, say N.
+
+if WAN
+
+# Generic HDLC
+config HDLC
+	tristate "Generic HDLC layer"
+	help
+	  Say Y to this option if your Linux box contains a WAN (Wide Area
+	  Network) card supported by this driver and you are planning to
+	  connect the box to a WAN.
+
+	  You will need supporting software from
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+	  Generic HDLC driver currently supports raw HDLC, Cisco HDLC, Frame
+	  Relay, synchronous Point-to-Point Protocol (PPP) and X.25.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called hdlc.
+
+	  If unsure, say N.
+
+config HDLC_RAW
+	tristate "Raw HDLC support"
+	depends on HDLC
+	help
+	  Generic HDLC driver supporting raw HDLC over WAN connections.
+
+	  If unsure, say N.
+
+config HDLC_RAW_ETH
+	tristate "Raw HDLC Ethernet device support"
+	depends on HDLC
+	help
+	  Generic HDLC driver supporting raw HDLC Ethernet device emulation
+	  over WAN connections.
+
+	  You will need it for Ethernet over HDLC bridges.
+
+	  If unsure, say N.
+
+config HDLC_CISCO
+	tristate "Cisco HDLC support"
+	depends on HDLC
+	help
+	  Generic HDLC driver supporting Cisco HDLC over WAN connections.
+
+	  If unsure, say N.
+
+config HDLC_FR
+	tristate "Frame Relay support"
+	depends on HDLC
+	help
+	  Generic HDLC driver supporting Frame Relay over WAN connections.
+
+	  If unsure, say N.
+
+config HDLC_PPP
+	tristate "Synchronous Point-to-Point Protocol (PPP) support"
+	depends on HDLC
+	help
+	  Generic HDLC driver supporting PPP over WAN connections.
+
+	  If unsure, say N.
+
+config HDLC_X25
+	tristate "X.25 protocol support"
+	depends on HDLC && (LAPB=m && HDLC=m || LAPB=y)
+	help
+	  Generic HDLC driver supporting X.25 over WAN connections.
+
+	  If unsure, say N.
+
+comment "X.25/LAPB support is disabled"
+	depends on HDLC && (LAPB!=m || HDLC!=m) && LAPB!=y
+
+source "drivers/net/wan/framer/Kconfig"
+
+config PCI200SYN
+	tristate "Goramo PCI200SYN support"
+	depends on HDLC && PCI
+	help
+	  Driver for PCI200SYN cards by Goramo sp. j.
+
+	  If you have such a card, say Y here and see
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+
+	  To compile this as a module, choose M here: the
+	  module will be called pci200syn.
+
+	  If unsure, say N.
+
+config WANXL
+	tristate "SBE Inc. wanXL support"
+	depends on HDLC && PCI
+	help
+	  Driver for wanXL PCI cards by SBE Inc.
+
+	  If you have such a card, say Y here and see
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+
+	  To compile this as a module, choose M here: the
+	  module will be called wanxl.
+
+	  If unsure, say N.
+
+config WANXL_BUILD_FIRMWARE
+	bool "rebuild wanXL firmware"
+	depends on WANXL && !PREVENT_FIRMWARE_BUILD
+	help
+	  Allows you to rebuild firmware run by the QUICC processor.
+	  It requires m68k toolchains and hexdump programs.
+
+	  You should never need this option, say N.
+
+config PC300TOO
+	tristate "Cyclades PC300 RSV/X21 alternative support"
+	depends on HDLC && PCI
+	help
+	  Alternative driver for PC300 RSV/X21 PCI cards made by
+	  Cyclades, Inc. If you have such a card, say Y here and see
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+
+	  To compile this as a module, choose M here: the module
+	  will be called pc300too.
+
+	  If unsure, say N here.
+
+config N2
+	tristate "SDL RISCom/N2 support"
+	depends on HDLC && ISA
+	help
+	  Driver for RISCom/N2 single or dual channel ISA cards by
+	  SDL Communications Inc.
+
+	  If you have such a card, say Y here and see
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+
+	  Note that N2csu and N2dds cards are not supported by this driver.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called n2.
+
+	  If unsure, say N.
+
+config C101
+	tristate "Moxa C101 support"
+	depends on HDLC && ISA
+	help
+	  Driver for C101 SuperSync ISA cards by Moxa Technologies Co., Ltd.
+
+	  If you have such a card, say Y here and see
+	  <http://www.kernel.org/pub/linux/utils/net/hdlc/>.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called c101.
+
+	  If unsure, say N.
+
+config FARSYNC
+	tristate "FarSync T-Series support"
+	depends on HDLC && PCI && HAS_IOPORT
+	help
+	  Support for the FarSync T-Series X.21 (and V.35/V.24) cards by
+	  FarSite Communications Ltd.
+
+	  Synchronous communication is supported on all ports at speeds up to
+	  8Mb/s (128K on V.24) using synchronous PPP, Cisco HDLC, raw HDLC,
+	  Frame Relay or X.25/LAPB.
+
+	  If you want the module to be automatically loaded when the interface
+	  is referenced then you should add "alias hdlcX farsync" to a file
+	  in /etc/modprobe.d/ for each interface, where X is 0, 1, 2, ..., or
+	  simply use "alias hdlc* farsync" to indicate all of them.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called farsync.
+
+config FSL_QMC_HDLC
+	tristate "Freescale QMC HDLC support"
+	depends on HDLC
+	depends on CPM_QMC
+	help
+	  HDLC support using the Freescale QUICC Multichannel Controller (QMC).
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called fsl_qmc_hdlc.
+
+	  If unsure, say N.
+
+config FSL_UCC_HDLC
+	tristate "Freescale QUICC Engine HDLC support"
+	depends on HDLC
+	depends on QUICC_ENGINE
+	help
+	  Driver for Freescale QUICC Engine HDLC controller. The driver
+	  supports HDLC in NMSI and TDM mode.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called fsl_ucc_hdlc.
+
+config SLIC_DS26522
+	tristate "Slic Maxim ds26522 card support"
+	depends on SPI
+	depends on FSL_SOC || ARCH_MXC || ARCH_LAYERSCAPE || COMPILE_TEST
+	select BITREVERSE
+	help
+	  This module initializes and configures the slic maxim card
+	  in T1 or E1 mode.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called slic_ds26522.
+
+config IXP4XX_HSS
+	tristate "Intel IXP4xx HSS (synchronous serial port) support"
+	depends on HDLC && IXP4XX_NPE && IXP4XX_QMGR
+	depends on ARCH_IXP4XX && OF
+	select MFD_SYSCON
+	help
+	  Say Y here if you want to use built-in HSS ports
+	  on IXP4xx processor.
+
+# X.25 network drivers
+config LAPBETHER
+	tristate "LAPB over Ethernet driver"
+	depends on LAPB && X25
+	help
+	  Driver for a pseudo device (typically called /dev/lapb0) which allows
+	  you to open an LAPB point-to-point connection to some other computer
+	  on your Ethernet network.
+
+	  In order to do this, you need to say Y or M to the driver for your
+	  Ethernet card as well as to "LAPB Data Link Driver".
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called lapbether.
+
+
+	  If unsure, say N.
+
+endif # WAN