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, 138 insertions, 0 deletions

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
new file mode 100644
index 000000000..9f81af350
--- /dev/null
+++ b/drivers/video/console/Kconfig
@@ -0,0 +1,138 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Video configuration
+#
+
+menu "Console display driver support"
+
+config VGA_CONSOLE
+	bool "VGA text console" if EXPERT || !X86
+	depends on ALPHA || X86 || \
+		(ARM && ARCH_FOOTBRIDGE) || \
+		(MIPS && (MIPS_MALTA || SIBYTE_BCM112X || SIBYTE_SB1250 || SIBYTE_BCM1x80 || SNI_RM))
+	select APERTURE_HELPERS if (DRM || FB || VFIO_PCI_CORE)
+	default y
+	help
+	  Saying Y here will allow you to use Linux in text mode through a
+	  display that complies with the generic VGA standard. Virtually
+	  everyone wants that.
+
+	  The program SVGATextMode can be used to utilize SVGA video cards to
+	  their full potential in text mode. Download it from
+	  <ftp://ibiblio.org/pub/Linux/utils/console/>.
+
+	  Say Y.
+
+config SGI_NEWPORT_CONSOLE
+	tristate "SGI Newport Console support"
+	depends on SGI_IP22 && HAS_IOMEM
+	select FONT_SUPPORT
+	help
+	  Say Y here if you want the console on the Newport aka XL graphics
+	  card of your Indy.  Most people say Y here.
+
+config DUMMY_CONSOLE
+	def_bool VT || VGA_CONSOLE || FRAMEBUFFER_CONSOLE
+
+config DUMMY_CONSOLE_COLUMNS
+	int "Initial number of console screen columns"
+	depends on DUMMY_CONSOLE && !(ARCH_FOOTBRIDGE && VGA_CONSOLE)
+	default 160 if PARISC
+	default 80
+	help
+	  On PA-RISC, the default value is 160, which should fit a 1280x1024
+	  monitor.
+	  Select 80 if you use a 640x480 resolution by default.
+
+config DUMMY_CONSOLE_ROWS
+	int "Initial number of console screen rows"
+	depends on DUMMY_CONSOLE && !(ARCH_FOOTBRIDGE && VGA_CONSOLE)
+	default 64 if PARISC
+	default 30 if ARM
+	default 25
+	help
+	  On PA-RISC, the default value is 64, which should fit a 1280x1024
+	  monitor.
+	  Select 25 if you use a 640x480 resolution by default.
+
+config FRAMEBUFFER_CONSOLE
+	bool "Framebuffer Console support"
+	depends on FB_CORE && !UML
+	default DRM_FBDEV_EMULATION
+	select VT_HW_CONSOLE_BINDING
+	select CRC32
+	select FONT_SUPPORT
+	help
+	  Low-level framebuffer-based console driver.
+
+config FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION
+	bool "Enable legacy fbcon hardware acceleration code"
+	depends on FRAMEBUFFER_CONSOLE
+	default y if PARISC
+	default n
+	help
+	  This option enables the fbcon (framebuffer text-based) hardware
+	  acceleration for graphics drivers which were written for the fbdev
+	  graphics interface.
+
+	  On modern machines, on mainstream machines (like x86-64) or when
+	  using a modern Linux distribution those fbdev drivers usually aren't used.
+	  So enabling this option wouldn't have any effect, which is why you want
+	  to disable this option on such newer machines.
+
+	  If you compile this kernel for older machines which still require the
+	  fbdev drivers, you may want to say Y.
+
+	  If unsure, select n.
+
+config FRAMEBUFFER_CONSOLE_DETECT_PRIMARY
+       bool "Map the console to the primary display device"
+       depends on FRAMEBUFFER_CONSOLE
+       default n
+	help
+	 If this option is selected, the framebuffer console will
+	 automatically select the primary display device (if the architecture
+	 supports this feature).  Otherwise, the framebuffer console will
+	 always select the first framebuffer driver that is loaded. The latter
+	 is the default behavior.
+
+	 You can always override the automatic selection of the primary device
+	 by using the fbcon=map: boot option.
+
+	 If unsure, select n.
+
+config FRAMEBUFFER_CONSOLE_ROTATION
+       bool "Framebuffer Console Rotation"
+       depends on FRAMEBUFFER_CONSOLE
+       help
+	 Enable display rotation for the framebuffer console.  This is done
+	 in software and may be significantly slower than a normally oriented
+	 display.  Note that the rotation is done at the console level only
+	 such that other users of the framebuffer will remain normally
+	 oriented.
+
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	bool "Framebuffer Console Deferred Takeover"
+	depends on FB=y && FRAMEBUFFER_CONSOLE && DUMMY_CONSOLE
+	help
+	  If enabled this defers the framebuffer console taking over the
+	  console from the dummy console until the first text is displayed on
+	  the console. This is useful in combination with the "quiet" kernel
+	  commandline option to keep the framebuffer contents initially put up
+	  by the firmware in place, rather then replacing the contents with a
+	  black screen as soon as fbcon loads.
+
+config STI_CONSOLE
+	bool "STI text console"
+	depends on PARISC && HAS_IOMEM
+	select FONT_SUPPORT
+	select CRC32
+	select STI_CORE
+	default y
+	help
+	  The STI console is the builtin display/keyboard on HP-PARISC
+	  machines.  Say Y here to build support for it into your kernel.
+	  The alternative is to use your primary serial port as a console.
+
+endmenu
+