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, 32 insertions, 0 deletions

diff --git a/drivers/clk/versatile/Kconfig b/drivers/clk/versatile/Kconfig
new file mode 100644
index 000000000..403f16495
--- /dev/null
+++ b/drivers/clk/versatile/Kconfig
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+menu "Clock driver for ARM Reference designs"
+	depends on HAS_IOMEM
+	depends on ARM || ARM64 || COMPILE_TEST
+
+config CLK_ICST
+	bool "Clock driver for ARM Reference designs ICST"
+	select REGMAP_MMIO
+	help
+	  Supports clocking on ARM Reference designs:
+	  - Integrator/AP and Integrator/CP
+	  - RealView PB1176, EB, PB11MP and PBX
+
+config CLK_SP810
+	bool "Clock driver for ARM SP810 System Controller"
+	default y if (ARCH_VEXPRESS && ARM)
+	help
+	  Supports clock muxing (REFCLK/TIMCLK to TIMERCLKEN0-3) capabilities
+	  of the ARM SP810 System Controller cell.
+
+config CLK_VEXPRESS_OSC
+	tristate "Clock driver for Versatile Express OSC clock generators"
+	depends on VEXPRESS_CONFIG
+	select REGMAP_MMIO
+	default y if ARCH_VEXPRESS
+	help
+	  Simple regmap-based driver driving clock generators on Versatile
+	  Express platforms hidden behind its configuration infrastructure,
+	  commonly known as OSCs.
+
+endmenu