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, 148 insertions, 0 deletions

diff --git a/net/bluetooth/Kconfig b/net/bluetooth/Kconfig
new file mode 100644
index 000000000..1cda01614
--- /dev/null
+++ b/net/bluetooth/Kconfig
@@ -0,0 +1,148 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Bluetooth subsystem configuration
+#
+
+menuconfig BT
+	tristate "Bluetooth subsystem support"
+	depends on !S390
+	depends on RFKILL || !RFKILL
+	select CRC16
+	select CRYPTO
+	select CRYPTO_LIB_AES
+	select CRYPTO_LIB_AES_CBC_MACS
+	select CRYPTO_ECDH
+	help
+	  Bluetooth is low-cost, low-power, short-range wireless technology.
+	  It was designed as a replacement for cables and other short-range
+	  technologies like IrDA.  Bluetooth operates in personal area range
+	  that typically extends up to 10 meters.  More information about
+	  Bluetooth can be found at <https://www.bluetooth.com/>.
+
+	  Linux Bluetooth subsystem consist of several layers:
+	     Bluetooth Core
+		HCI device and connection manager, scheduler
+		SCO audio links
+		L2CAP (Logical Link Control and Adaptation Protocol)
+		SMP (Security Manager Protocol) on LE (Low Energy) links
+		ISO isochronous links
+	     HCI Device drivers (Interface to the hardware)
+	     RFCOMM Module (RFCOMM Protocol)  
+	     BNEP Module (Bluetooth Network Encapsulation Protocol)
+	     HIDP Module (Human Interface Device Protocol)
+
+	  Say Y here to compile Bluetooth support into the kernel or say M to
+	  compile it as module (bluetooth).
+
+	  To use Linux Bluetooth subsystem, you will need several user-space
+	  utilities like hciconfig and bluetoothd.  These utilities and updates
+	  to Bluetooth kernel modules are provided in the BlueZ packages.  For
+	  more information, see <http://www.bluez.org/>.
+
+config BT_BREDR
+	bool "Bluetooth Classic (BR/EDR) features"
+	depends on BT
+	default y
+	help
+	  Bluetooth Classic includes support for Basic Rate (BR)
+	  available with Bluetooth version 1.0b or later and support
+	  for Enhanced Data Rate (EDR) available with Bluetooth
+	  version 2.0 or later.
+
+source "net/bluetooth/rfcomm/Kconfig"
+
+source "net/bluetooth/bnep/Kconfig"
+
+source "net/bluetooth/hidp/Kconfig"
+
+config BT_LE
+	bool "Bluetooth Low Energy (LE) features"
+	depends on BT
+	default y
+	help
+	  Bluetooth Low Energy includes support low-energy physical
+	  layer available with Bluetooth version 4.0 or later.
+
+config BT_LE_L2CAP_ECRED
+	bool "Bluetooth L2CAP Enhanced Credit Flow Control"
+	depends on BT_LE
+	default y
+	help
+	  Bluetooth Low Energy L2CAP Enhanced Credit Flow Control available with
+	  Bluetooth version 5.2 or later.
+
+	  This can be overridden by passing bluetooth.enable_ecred=[1|0]
+	  on the kernel commandline.
+
+config BT_6LOWPAN
+	tristate "Bluetooth 6LoWPAN support"
+	depends on BT && BT_LE && 6LOWPAN
+	help
+	  IPv6 compression over Bluetooth Low Energy.
+
+config BT_LEDS
+	bool "Enable LED triggers"
+	depends on BT
+	depends on LEDS_CLASS
+	select LEDS_TRIGGERS
+	help
+	  This option selects a few LED triggers for different
+	  Bluetooth events.
+
+config BT_MSFTEXT
+	bool "Enable Microsoft extensions"
+	depends on BT
+	help
+	  This options enables support for the Microsoft defined HCI
+	  vendor extensions.
+
+config BT_AOSPEXT
+	bool "Enable Android Open Source Project extensions"
+	depends on BT
+	help
+	  This options enables support for the Android Open Source
+	  Project defined HCI vendor extensions.
+
+config BT_DEBUGFS
+	bool "Export Bluetooth internals in debugfs"
+	depends on BT && DEBUG_FS
+	default y
+	help
+	  Provide extensive information about internal Bluetooth states
+	  in debugfs.
+
+config BT_SELFTEST
+	bool "Bluetooth self testing support"
+	depends on BT && DEBUG_KERNEL
+	help
+	  Run self tests when initializing the Bluetooth subsystem.  This
+	  is a developer option and can cause significant delay when booting
+	  the system.
+
+	  When the Bluetooth subsystem is built as module, then the test
+	  cases are run first thing at module load time.  When the Bluetooth
+	  subsystem is compiled into the kernel image, then the test cases
+	  are run late in the initcall hierarchy.
+
+config BT_SELFTEST_ECDH
+	bool "ECDH test cases"
+	depends on BT_LE && BT_SELFTEST
+	help
+	  Run test cases for ECDH cryptographic functionality used by the
+	  Bluetooth Low Energy Secure Connections feature.
+
+config BT_SELFTEST_SMP
+	bool "SMP test cases"
+	depends on BT_LE && BT_SELFTEST
+	help
+	  Run test cases for SMP cryptographic functionality, including both
+	  legacy SMP as well as the Secure Connections features.
+
+config BT_FEATURE_DEBUG
+	bool "Enable runtime option for debugging statements"
+	depends on BT && !DYNAMIC_DEBUG
+	help
+	  This provides an option to enable/disable debugging statements
+	  at runtime via the experimental features interface.
+
+source "drivers/bluetooth/Kconfig"