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, 115 insertions, 0 deletions

diff --git a/sound/soc/sof/nocodec.c b/sound/soc/sof/nocodec.c
new file mode 100644
index 000000000..34744f8ae
--- /dev/null
+++ b/sound/soc/sof/nocodec.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+//
+// This file is provided under a dual BSD/GPLv2 license.  When using or
+// redistributing this file, you may do so under either license.
+//
+// Copyright(c) 2018 Intel Corporation
+//
+// Author: Liam Girdwood <liam.r.girdwood@linux.intel.com>
+//
+
+#include <linux/module.h>
+#include <sound/sof.h>
+#include "sof-audio.h"
+#include "sof-priv.h"
+
+static struct snd_soc_card sof_nocodec_card = {
+	.name = "nocodec", /* the sof- prefix is added by the core */
+	.owner = THIS_MODULE
+};
+
+static int sof_nocodec_bes_setup(struct device *dev,
+				 struct snd_soc_dai_driver *drv,
+				 struct snd_soc_dai_link *links,
+				 int link_num)
+{
+	struct snd_soc_card *card = &sof_nocodec_card;
+	struct snd_soc_dai_link_component *dlc;
+	int i;
+
+	if (!drv || !links)
+		return -EINVAL;
+
+	/* set up BE dai_links */
+	for (i = 0; i < link_num; i++) {
+		dlc = devm_kcalloc(dev, 2, sizeof(*dlc), GFP_KERNEL);
+		if (!dlc)
+			return -ENOMEM;
+
+		links[i].name = devm_kasprintf(dev, GFP_KERNEL,
+					       "NoCodec-%d", i);
+		if (!links[i].name)
+			return -ENOMEM;
+
+		links[i].stream_name = links[i].name;
+
+		links[i].cpus = &dlc[0];
+		links[i].codecs = &snd_soc_dummy_dlc;
+		links[i].platforms = &dlc[1];
+
+		links[i].num_cpus = 1;
+		links[i].num_codecs = 1;
+		links[i].num_platforms = 1;
+
+		links[i].id = i;
+		links[i].no_pcm = 1;
+		links[i].cpus->dai_name = drv[i].name;
+		links[i].platforms->name = dev_name(dev->parent);
+
+		links[i].playback_only =  drv[i].playback.channels_min && !drv[i].capture.channels_min;
+		links[i].capture_only  = !drv[i].playback.channels_min &&  drv[i].capture.channels_min;
+
+		links[i].be_hw_params_fixup = sof_pcm_dai_link_fixup;
+	}
+
+	card->dai_link = links;
+	card->num_links = link_num;
+
+	return 0;
+}
+
+static int sof_nocodec_setup(struct device *dev, struct snd_soc_acpi_mach *mach)
+{
+	u32 num_dai_drivers = mach->mach_params.num_dai_drivers;
+	struct snd_soc_dai_driver *dai_drivers = mach->mach_params.dai_drivers;
+	struct snd_soc_dai_link *links;
+
+	/* create dummy BE dai_links */
+	links = devm_kcalloc(dev, num_dai_drivers, sizeof(struct snd_soc_dai_link), GFP_KERNEL);
+	if (!links)
+		return -ENOMEM;
+
+	return sof_nocodec_bes_setup(dev, dai_drivers, links, num_dai_drivers);
+}
+
+static int sof_nocodec_probe(struct platform_device *pdev)
+{
+	struct snd_soc_card *card = &sof_nocodec_card;
+	struct snd_soc_acpi_mach *mach;
+	int ret;
+
+	card->dev = &pdev->dev;
+	mach = pdev->dev.platform_data;
+
+	snd_soc_card_set_topology_name(card, "sof");
+
+	ret = sof_nocodec_setup(card->dev, mach);
+	if (ret < 0)
+		return ret;
+
+	return devm_snd_soc_register_card(&pdev->dev, card);
+}
+
+static struct platform_driver sof_nocodec_audio = {
+	.probe = sof_nocodec_probe,
+	.driver = {
+		.name = "sof-nocodec",
+		.pm = &snd_soc_pm_ops,
+	},
+};
+module_platform_driver(sof_nocodec_audio)
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("ASoC sof nocodec");
+MODULE_AUTHOR("Liam Girdwood");
+MODULE_ALIAS("platform:sof-nocodec");