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, 204 insertions, 0 deletions

diff --git a/arch/mips/generic/init.c b/arch/mips/generic/init.c
new file mode 100644
index 000000000..1d712eac1
--- /dev/null
+++ b/arch/mips/generic/init.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2016 Imagination Technologies
+ * Author: Paul Burton <paul.burton@mips.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/clocksource.h>
+#include <linux/init.h>
+#include <linux/irqchip.h>
+#include <linux/of_clk.h>
+#include <linux/of_fdt.h>
+
+#include <asm/bootinfo.h>
+#include <asm/fw/fw.h>
+#include <asm/irq_cpu.h>
+#include <asm/machine.h>
+#include <asm/mips-cps.h>
+#include <asm/prom.h>
+#include <asm/smp-ops.h>
+#include <asm/time.h>
+
+static __initconst const void *fdt;
+static __initconst const struct mips_machine *mach;
+static __initconst const void *mach_match_data;
+
+void __init prom_init(void)
+{
+	plat_get_fdt();
+	BUG_ON(!fdt);
+}
+
+void __init *plat_get_fdt(void)
+{
+	const struct mips_machine *check_mach;
+	const struct of_device_id *match;
+
+	if (fdt)
+		/* Already set up */
+		return (void *)fdt;
+
+	fdt = (void *)get_fdt();
+	if (fdt && !fdt_check_header(fdt)) {
+		/*
+		 * We have been provided with the appropriate device tree for
+		 * the board. Make use of it & search for any machine struct
+		 * based upon the root compatible string.
+		 */
+		for_each_mips_machine(check_mach) {
+			match = mips_machine_is_compatible(check_mach, fdt);
+			if (match) {
+				mach = check_mach;
+				mach_match_data = match->data;
+				break;
+			}
+		}
+	} else if (IS_ENABLED(CONFIG_LEGACY_BOARDS)) {
+		/*
+		 * We weren't booted using the UHI boot protocol, but do
+		 * support some number of boards with legacy boot protocols.
+		 * Attempt to find the right one.
+		 */
+		for_each_mips_machine(check_mach) {
+			if (!check_mach->detect)
+				continue;
+
+			if (!check_mach->detect())
+				continue;
+
+			mach = check_mach;
+		}
+
+		/*
+		 * If we don't recognise the machine then we can't continue, so
+		 * die here.
+		 */
+		BUG_ON(!mach);
+
+		/* Retrieve the machine's FDT */
+		fdt = mach->fdt;
+	}
+	return (void *)fdt;
+}
+
+#ifdef CONFIG_RELOCATABLE
+
+void __init plat_fdt_relocated(void *new_location)
+{
+	/*
+	 * reset fdt as the cached value would point to the location
+	 * before relocations happened and update the location argument
+	 * if it was passed using UHI
+	 */
+	fdt = NULL;
+
+	if (fw_arg0 == -2)
+		fw_arg1 = (unsigned long)new_location;
+}
+
+#endif /* CONFIG_RELOCATABLE */
+
+void __init plat_mem_setup(void)
+{
+	if (mach && mach->fixup_fdt)
+		fdt = mach->fixup_fdt(fdt, mach_match_data);
+
+	fw_init_cmdline();
+	__dt_setup_arch((void *)fdt);
+}
+
+void __init device_tree_init(void)
+{
+	unflatten_and_copy_device_tree();
+	mips_cpc_probe();
+
+	if (!register_cps_smp_ops())
+		return;
+	if (!register_vsmp_smp_ops())
+		return;
+
+	register_up_smp_ops();
+}
+
+int __init apply_mips_fdt_fixups(void *fdt_out, size_t fdt_out_size,
+				 const void *fdt_in,
+				 const struct mips_fdt_fixup *fixups)
+{
+	int err;
+
+	err = fdt_open_into(fdt_in, fdt_out, fdt_out_size);
+	if (err) {
+		pr_err("Failed to open FDT\n");
+		return err;
+	}
+
+	for (; fixups->apply; fixups++) {
+		err = fixups->apply(fdt_out);
+		if (err) {
+			pr_err("Failed to apply FDT fixup \"%s\"\n",
+			       fixups->description);
+			return err;
+		}
+	}
+
+	err = fdt_pack(fdt_out);
+	if (err)
+		pr_err("Failed to pack FDT\n");
+	return err;
+}
+
+void __init plat_time_init(void)
+{
+	struct device_node *np;
+	struct clk *clk;
+
+	of_clk_init(NULL);
+
+	if (!cpu_has_counter) {
+		mips_hpt_frequency = 0;
+	} else if (mach && mach->measure_hpt_freq) {
+		mips_hpt_frequency = mach->measure_hpt_freq();
+	} else {
+		np = of_get_cpu_node(0, NULL);
+		if (!np) {
+			pr_err("Failed to get CPU node\n");
+			return;
+		}
+
+		clk = of_clk_get(np, 0);
+		if (IS_ERR(clk)) {
+			pr_err("Failed to get CPU clock: %ld\n", PTR_ERR(clk));
+			return;
+		}
+
+		mips_hpt_frequency = clk_get_rate(clk);
+		clk_put(clk);
+
+		switch (boot_cpu_type()) {
+		case CPU_20KC:
+		case CPU_25KF:
+			/* The counter runs at the CPU clock rate */
+			break;
+		default:
+			/* The counter runs at half the CPU clock rate */
+			mips_hpt_frequency /= 2;
+			break;
+		}
+	}
+
+	timer_probe();
+}
+
+void __init arch_init_irq(void)
+{
+	struct device_node *intc_node;
+
+	intc_node = of_find_compatible_node(NULL, NULL,
+					    "mti,cpu-interrupt-controller");
+	if (!cpu_has_veic && !intc_node)
+		mips_cpu_irq_init();
+	of_node_put(intc_node);
+
+	irqchip_init();
+}