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, 80 insertions, 0 deletions

diff --git a/drivers/clk/sprd/div.c b/drivers/clk/sprd/div.c
new file mode 100644
index 000000000..cd57163a7
--- /dev/null
+++ b/drivers/clk/sprd/div.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Spreadtrum divider clock driver
+//
+// Copyright (C) 2017 Spreadtrum, Inc.
+// Author: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
+
+#include <linux/clk-provider.h>
+
+#include "div.h"
+
+static int sprd_div_determine_rate(struct clk_hw *hw,
+				   struct clk_rate_request *req)
+{
+	struct sprd_div *cd = hw_to_sprd_div(hw);
+
+	return divider_determine_rate(&cd->common.hw, req, NULL, cd->div.width, 0);
+}
+
+unsigned long sprd_div_helper_recalc_rate(struct sprd_clk_common *common,
+					  const struct sprd_div_internal *div,
+					  unsigned long parent_rate)
+{
+	unsigned long val;
+	unsigned int reg;
+
+	regmap_read(common->regmap, common->reg + div->offset, &reg);
+	val = reg >> div->shift;
+	val &= (1 << div->width) - 1;
+
+	return divider_recalc_rate(&common->hw, parent_rate, val, NULL, 0,
+				   div->width);
+}
+EXPORT_SYMBOL_GPL(sprd_div_helper_recalc_rate);
+
+static unsigned long sprd_div_recalc_rate(struct clk_hw *hw,
+					  unsigned long parent_rate)
+{
+	struct sprd_div *cd = hw_to_sprd_div(hw);
+
+	return sprd_div_helper_recalc_rate(&cd->common, &cd->div, parent_rate);
+}
+
+int sprd_div_helper_set_rate(const struct sprd_clk_common *common,
+			     const struct sprd_div_internal *div,
+			     unsigned long rate,
+			     unsigned long parent_rate)
+{
+	unsigned long val;
+	unsigned int reg;
+
+	val = divider_get_val(rate, parent_rate, NULL,
+			      div->width, 0);
+
+	regmap_read(common->regmap, common->reg + div->offset, &reg);
+	reg &= ~GENMASK(div->width + div->shift - 1, div->shift);
+
+	regmap_write(common->regmap, common->reg + div->offset,
+			  reg | (val << div->shift));
+
+	return 0;
+
+}
+EXPORT_SYMBOL_GPL(sprd_div_helper_set_rate);
+
+static int sprd_div_set_rate(struct clk_hw *hw, unsigned long rate,
+			     unsigned long parent_rate)
+{
+	struct sprd_div *cd = hw_to_sprd_div(hw);
+
+	return sprd_div_helper_set_rate(&cd->common, &cd->div,
+					rate, parent_rate);
+}
+
+const struct clk_ops sprd_div_ops = {
+	.recalc_rate = sprd_div_recalc_rate,
+	.determine_rate = sprd_div_determine_rate,
+	.set_rate = sprd_div_set_rate,
+};
+EXPORT_SYMBOL_GPL(sprd_div_ops);