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, 77 insertions, 0 deletions

diff --git a/drivers/edac/layerscape_edac.c b/drivers/edac/layerscape_edac.c
new file mode 100644
index 000000000..a2caa7fc5
--- /dev/null
+++ b/drivers/edac/layerscape_edac.c
@@ -0,0 +1,77 @@
+/*
+ * Freescale Memory Controller kernel module
+ *
+ * Author: York Sun <york.sun@nxp.com>
+ *
+ * Copyright 2016 NXP Semiconductor
+ *
+ * Derived from mpc85xx_edac.c
+ * Author: Dave Jiang <djiang@mvista.com>
+ *
+ * 2006-2007 (c) MontaVista Software, Inc. This file is licensed under
+ * the terms of the GNU General Public License version 2. This program
+ * is licensed "as is" without any warranty of any kind, whether express
+ * or implied.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "edac_module.h"
+#include "fsl_ddr_edac.h"
+
+static const struct of_device_id fsl_ddr_mc_err_of_match[] = {
+	{ .compatible = "fsl,qoriq-memory-controller", },
+	{ .compatible = "nxp,imx9-memory-controller", .data = (void *)TYPE_IMX9, },
+	{},
+};
+MODULE_DEVICE_TABLE(of, fsl_ddr_mc_err_of_match);
+
+static struct platform_driver fsl_ddr_mc_err_driver = {
+	.probe = fsl_mc_err_probe,
+	.remove = fsl_mc_err_remove,
+	.driver = {
+		.name = "fsl_ddr_mc_err",
+		.of_match_table = fsl_ddr_mc_err_of_match,
+	},
+};
+
+static int __init fsl_ddr_mc_init(void)
+{
+	int res;
+
+	if (ghes_get_devices())
+		return -EBUSY;
+
+	/* make sure error reporting method is sane */
+	switch (edac_op_state) {
+	case EDAC_OPSTATE_POLL:
+	case EDAC_OPSTATE_INT:
+		break;
+	default:
+		edac_op_state = EDAC_OPSTATE_INT;
+		break;
+	}
+
+	res = platform_driver_register(&fsl_ddr_mc_err_driver);
+	if (res) {
+		pr_err("MC fails to register\n");
+		return res;
+	}
+
+	return 0;
+}
+
+module_init(fsl_ddr_mc_init);
+
+static void __exit fsl_ddr_mc_exit(void)
+{
+	platform_driver_unregister(&fsl_ddr_mc_err_driver);
+}
+
+module_exit(fsl_ddr_mc_exit);
+
+MODULE_DESCRIPTION("Freescale Layerscape EDAC driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("NXP Semiconductor");
+module_param(edac_op_state, int, 0444);
+MODULE_PARM_DESC(edac_op_state, "EDAC Error Reporting state: 0=Poll, 2=Interrupt");