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

3 files changed, 157 insertions, 0 deletions

diff --git a/Documentation/admin-guide/auxdisplay/cfag12864b.rst b/Documentation/admin-guide/auxdisplay/cfag12864b.rst
new file mode 100644
index 000000000..da385d851
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/cfag12864b.rst
@@ -0,0 +1,98 @@
+===================================
+cfag12864b LCD Driver Documentation
+===================================
+
+:License:		GPLv2
+:Author & Maintainer:	Miguel Ojeda <ojeda@kernel.org>
+:Date:			2006-10-27
+
+
+
+.. INDEX
+
+	1. DRIVER INFORMATION
+	2. DEVICE INFORMATION
+	3. WIRING
+	4. USERSPACE PROGRAMMING
+
+1. Driver Information
+---------------------
+
+This driver supports a cfag12864b LCD.
+
+
+2. Device Information
+---------------------
+
+:Manufacturer:	Crystalfontz
+:Device Name:	Crystalfontz 12864b LCD Series
+:Device Code:	cfag12864b
+:Webpage:	http://www.crystalfontz.com
+:Device Webpage: http://www.crystalfontz.com/products/12864b/
+:Type:		LCD (Liquid Crystal Display)
+:Width:		128
+:Height:	64
+:Colors:	2 (B/N)
+:Controller:	ks0108
+:Controllers:	2
+:Pages:		8 each controller
+:Addresses:	64 each page
+:Data size:	1 byte each address
+:Memory size:	2 * 8 * 64 * 1 = 1024 bytes = 1 Kbyte
+
+
+3. Wiring
+---------
+
+The cfag12864b LCD Series don't have official wiring.
+
+The common wiring is done to the parallel port as shown::
+
+  Parallel Port                          cfag12864b
+
+    Name Pin#                            Pin# Name
+
+  Strobe ( 1)------------------------------(17) Enable
+  Data 0 ( 2)------------------------------( 4) Data 0
+  Data 1 ( 3)------------------------------( 5) Data 1
+  Data 2 ( 4)------------------------------( 6) Data 2
+  Data 3 ( 5)------------------------------( 7) Data 3
+  Data 4 ( 6)------------------------------( 8) Data 4
+  Data 5 ( 7)------------------------------( 9) Data 5
+  Data 6 ( 8)------------------------------(10) Data 6
+  Data 7 ( 9)------------------------------(11) Data 7
+         (10)                      [+5v]---( 1) Vdd
+         (11)                      [GND]---( 2) Ground
+         (12)                      [+5v]---(14) Reset
+         (13)                      [GND]---(15) Read / Write
+    Line (14)------------------------------(13) Controller Select 1
+         (15)
+    Init (16)------------------------------(12) Controller Select 2
+  Select (17)------------------------------(16) Data / Instruction
+  Ground (18)---[GND]              [+5v]---(19) LED +
+  Ground (19)---[GND]
+  Ground (20)---[GND]              E    A             Values:
+  Ground (21)---[GND]       [GND]---[P1]---(18) Vee    - R = Resistor = 22 ohm
+  Ground (22)---[GND]                |                 - P1 = Preset = 10 Kohm
+  Ground (23)---[GND]       ----   S ------( 3) V0     - P2 = Preset = 1 Kohm
+  Ground (24)---[GND]       |  |
+  Ground (25)---[GND] [GND]---[P2]---[R]---(20) LED -
+
+
+4. Userspace Programming
+------------------------
+
+The cfag12864bfb describes a framebuffer device (/dev/fbX).
+
+It has a size of 1024 bytes = 1 Kbyte.
+Each bit represents one pixel. If the bit is high, the pixel will
+turn on. If the pixel is low, the pixel will turn off.
+
+You can use the framebuffer as a file: fopen, fwrite, fclose...
+Although the LCD won't get updated until the next refresh time arrives.
+
+Also, you can mmap the framebuffer: open & mmap, munmap & close...
+which is the best option for most uses.
+
+Check samples/auxdisplay/cfag12864b-example.c
+for a real working userspace complete program with usage examples.
diff --git a/Documentation/admin-guide/auxdisplay/index.rst b/Documentation/admin-guide/auxdisplay/index.rst
new file mode 100644
index 000000000..31eae0825
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/index.rst
@@ -0,0 +1,9 @@
+=========================
+Auxiliary Display Support
+=========================
+
+.. toctree::
+    :maxdepth: 1
+
+    ks0108.rst
+    cfag12864b.rst
diff --git a/Documentation/admin-guide/auxdisplay/ks0108.rst b/Documentation/admin-guide/auxdisplay/ks0108.rst
new file mode 100644
index 000000000..a7d3fe509
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/ks0108.rst
@@ -0,0 +1,50 @@
+==========================================
+ks0108 LCD Controller Driver Documentation
+==========================================
+
+:License:		GPLv2
+:Author & Maintainer:	Miguel Ojeda <ojeda@kernel.org>
+:Date:			2006-10-27
+
+
+
+.. INDEX
+
+	1. DRIVER INFORMATION
+	2. DEVICE INFORMATION
+	3. WIRING
+
+
+1. Driver Information
+---------------------
+
+This driver supports the ks0108 LCD controller.
+
+
+2. Device Information
+---------------------
+
+:Manufacturer:	Samsung
+:Device Name:	KS0108 LCD Controller
+:Device Code:	ks0108
+:Webpage:	-
+:Device Webpage: -
+:Type:		LCD Controller (Liquid Crystal Display Controller)
+:Width:		64
+:Height:	64
+:Colors:	2 (B/N)
+:Pages:		8
+:Addresses:	64 each page
+:Data size:	1 byte each address
+:Memory size:	8 * 64 * 1 = 512 bytes
+
+
+3. Wiring
+---------
+
+The driver supports data parallel port wiring.
+
+If you aren't building LCD related hardware, you should check
+your LCD specific wiring information in the same folder.
+
+For example, check Documentation/admin-guide/auxdisplay/cfag12864b.rst