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, 163 insertions, 0 deletions

diff --git a/Documentation/process/kernel-enforcement-statement.rst b/Documentation/process/kernel-enforcement-statement.rst
new file mode 100644
index 000000000..dc2d813b2
--- /dev/null
+++ b/Documentation/process/kernel-enforcement-statement.rst
@@ -0,0 +1,163 @@
+.. _process_statement_kernel:
+
+Linux Kernel Enforcement Statement
+----------------------------------
+
+As developers of the Linux kernel, we have a keen interest in how our software
+is used and how the license for our software is enforced.  Compliance with the
+reciprocal sharing obligations of GPL-2.0 is critical to the long-term
+sustainability of our software and community.
+
+Although there is a right to enforce the separate copyright interests in the
+contributions made to our community, we share an interest in ensuring that
+individual enforcement actions are conducted in a manner that benefits our
+community and do not have an unintended negative impact on the health and
+growth of our software ecosystem.  In order to deter unhelpful enforcement
+actions, we agree that it is in the best interests of our development
+community to undertake the following commitment to users of the Linux kernel
+on behalf of ourselves and any successors to our copyright interests:
+
+    Notwithstanding the termination provisions of the GPL-2.0, we agree that
+    it is in the best interests of our development community to adopt the
+    following provisions of GPL-3.0 as additional permissions under our
+    license with respect to any non-defensive assertion of rights under the
+    license.
+
+	However, if you cease all violation of this License, then your license
+	from a particular copyright holder is reinstated (a) provisionally,
+	unless and until the copyright holder explicitly and finally
+	terminates your license, and (b) permanently, if the copyright holder
+	fails to notify you of the violation by some reasonable means prior to
+	60 days after the cessation.
+
+	Moreover, your license from a particular copyright holder is
+	reinstated permanently if the copyright holder notifies you of the
+	violation by some reasonable means, this is the first time you have
+	received notice of violation of this License (for any work) from that
+	copyright holder, and you cure the violation prior to 30 days after
+	your receipt of the notice.
+
+Our intent in providing these assurances is to encourage more use of the
+software.  We want companies and individuals to use, modify and distribute
+this software.  We want to work with users in an open and transparent way to
+eliminate any uncertainty about our expectations regarding compliance or
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+failed to resolve the problem.
+
+Finally, once a non-compliance issue is resolved, we hope the user will feel
+welcome to join us in our efforts on this project.  Working together, we will
+be stronger.
+
+Except where noted below, we speak only for ourselves, and not for any company
+we might work for today, have in the past, or will in the future.
+
+  - Laura Abbott
+  - Bjorn Andersson (Linaro)
+  - Andrea Arcangeli
+  - Neil Armstrong
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+  - Khalid Aziz
+  - Ralf Baechle
+  - Felipe Balbi
+  - Arnd Bergmann
+  - Ard Biesheuvel
+  - Tim Bird
+  - Paolo Bonzini
+  - Christian Borntraeger
+  - Mark Brown (Linaro)
+  - Paul Burton
+  - Javier Martinez Canillas
+  - Rob Clark
+  - Kees Cook (Google)
+  - Jonathan Corbet
+  - Dennis Dalessandro
+  - Vivien Didelot (Savoir-faire Linux)
+  - Hans de Goede
+  - Mel Gorman (SUSE)
+  - Sven Eckelmann
+  - Alex Elder (Linaro)
+  - Fabio Estevam
+  - Larry Finger
+  - Bhumika Goyal
+  - Andy Gross
+  - Juergen Gross
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+  - Ulf Hansson
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+  - Krzysztof Kozlowski
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+  - Julia Lawall
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+  - Chuck Lever (Oracle)
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+  - Shaohua Li
+  - Xin Long
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+  - Catalin Marinas (Arm Ltd)
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+  - Chris Mason
+  - Paul E. McKenney
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+  - David S. Miller
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+  - Kuninori Morimoto
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