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, 202 insertions, 0 deletions

diff --git a/Documentation/process/kernel-driver-statement.rst b/Documentation/process/kernel-driver-statement.rst
new file mode 100644
index 000000000..a849790a6
--- /dev/null
+++ b/Documentation/process/kernel-driver-statement.rst
@@ -0,0 +1,202 @@
+.. _process_statement_driver:
+
+Kernel Driver Statement
+-----------------------
+
+Position Statement on Linux Kernel Modules
+==========================================
+
+
+We, the undersigned Linux kernel developers, consider any closed-source
+Linux kernel module or driver to be harmful and undesirable. We have
+repeatedly found them to be detrimental to Linux users, businesses, and
+the greater Linux ecosystem. Such modules negate the openness,
+stability, flexibility, and maintainability of the Linux development
+model and shut their users off from the expertise of the Linux
+community. Vendors that provide closed-source kernel modules force their
+customers to give up key Linux advantages or choose new vendors.
+Therefore, in order to take full advantage of the cost savings and
+shared support benefits open source has to offer, we urge vendors to
+adopt a policy of supporting their customers on Linux with open-source
+kernel code.
+
+We speak only for ourselves, and not for any company we might work for
+today, have in the past, or will in the future.
+
+ - Dave Airlie
+ - Nick Andrew
+ - Jens Axboe
+ - Ralf Baechle
+ - Felipe Balbi
+ - Ohad Ben-Cohen
+ - Muli Ben-Yehuda
+ - Jiri Benc
+ - Arnd Bergmann
+ - Thomas Bogendoerfer
+ - Vitaly Bordug
+ - James Bottomley
+ - Josh Boyer
+ - Neil Brown
+ - Mark Brown
+ - David Brownell
+ - Michael Buesch
+ - Franck Bui-Huu
+ - Adrian Bunk
+ - François Cami
+ - Ralph Campbell
+ - Luiz Fernando N. Capitulino
+ - Mauro Carvalho Chehab
+ - Denis Cheng
+ - Jonathan Corbet
+ - Glauber Costa
+ - Alan Cox
+ - Magnus Damm
+ - Ahmed S. Darwish
+ - Robert P. J. Day
+ - Hans de Goede
+ - Arnaldo Carvalho de Melo
+ - Helge Deller
+ - Jean Delvare
+ - Mathieu Desnoyers
+ - Sven-Thorsten Dietrich
+ - Alexey Dobriyan
+ - Daniel Drake
+ - Alex Dubov
+ - Randy Dunlap
+ - Michael Ellerman
+ - Pekka Enberg
+ - Jan Engelhardt
+ - Mark Fasheh
+ - J. Bruce Fields
+ - Larry Finger
+ - Jeremy Fitzhardinge
+ - Mike Frysinger
+ - Kumar Gala
+ - Robin Getz
+ - Liam Girdwood
+ - Jan-Benedict Glaw
+ - Thomas Gleixner
+ - Brice Goglin
+ - Cyrill Gorcunov
+ - Andy Gospodarek
+ - Thomas Graf
+ - Krzysztof Halasa
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+ - Stephen Hemminger
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+ - Benjamin Herrenschmidt
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+ - Mike Isely
+ - Takashi Iwai
+ - Olof Johansson
+ - Dave Jones
+ - Jesper Juhl
+ - Matthias Kaehlcke
+ - Kenji Kaneshige
+ - Jan Kara
+ - Jeremy Kerr
+ - Russell King
+ - Olaf Kirch
+ - Roel Kluin
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+ - Ingo Molnar
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+ - Holger Schurig
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