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, 95 insertions, 0 deletions

diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
new file mode 100644
index 000000000..a7144d275
--- /dev/null
+++ b/drivers/video/Kconfig
@@ -0,0 +1,95 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Video configuration
+#
+
+menu "Graphics support"
+
+config APERTURE_HELPERS
+	bool
+	help
+	  Support tracking and hand-over of aperture ownership. Required
+	  by graphics drivers for firmware-provided framebuffers.
+
+config SCREEN_INFO
+	bool
+	default n
+
+config STI_CORE
+	bool
+	depends on PARISC
+	help
+	  STI refers to the HP "Standard Text Interface" which is a set of
+	  BIOS routines contained in a ROM chip in HP PA-RISC based machines.
+
+config VIDEO
+	bool
+	default n
+
+source "drivers/auxdisplay/Kconfig"
+
+if HAS_IOMEM
+
+config HAVE_FB_ATMEL
+	bool
+
+source "drivers/char/agp/Kconfig"
+
+source "drivers/gpu/vga/Kconfig"
+
+source "drivers/gpu/Kconfig"
+source "drivers/gpu/host1x/Kconfig"
+source "drivers/gpu/ipu-v3/Kconfig"
+source "drivers/gpu/nova-core/Kconfig"
+
+source "drivers/gpu/drm/Kconfig"
+
+menu "Frame buffer Devices"
+source "drivers/video/fbdev/Kconfig"
+endmenu
+
+source "drivers/video/backlight/Kconfig"
+
+config VGASTATE
+       tristate
+       default n
+
+config VIDEOMODE_HELPERS
+	bool
+
+config HDMI
+	bool
+
+endif # HAS_IOMEM
+
+config FIRMWARE_EDID
+	bool "Enable firmware EDID"
+	depends on EFI_GENERIC_STUB || X86
+	help
+	  This enables access to the EDID transferred from the firmware.
+	  On EFI systems, the EDID comes from the same device as the
+	  primary GOP. On x86 with BIOS, it comes from the VESA BIOS.
+	  DRM display drivers will be able to export the information
+	  to userspace.
+
+	  Also enable this if DDC/I2C transfers do not work for your driver
+	  and if you are using nvidiafb, i810fb or savagefb.
+
+	  In general, choosing Y for this option is safe.  If you
+	  experience extremely long delays while booting before you get
+	  something on your display, try setting this to N.  Matrox cards in
+	  combination with certain motherboards and monitors are known to
+	  suffer from this problem.
+
+if VT
+	source "drivers/video/console/Kconfig"
+endif
+
+if FB_CORE || SGI_NEWPORT_CONSOLE
+	source "drivers/video/logo/Kconfig"
+
+endif
+
+source "drivers/gpu/trace/Kconfig"
+
+endmenu