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, 45 insertions, 0 deletions

diff --git a/drivers/hid/hid-macally.c b/drivers/hid/hid-macally.c
new file mode 100644
index 000000000..fe7576458
--- /dev/null
+++ b/drivers/hid/hid-macally.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ *  HID driver for quirky Macally devices
+ *
+ *  Copyright (c) 2019 Alex Henrie <alexhenrie24@gmail.com>
+ */
+
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+MODULE_AUTHOR("Alex Henrie <alexhenrie24@gmail.com>");
+MODULE_DESCRIPTION("Macally devices");
+MODULE_LICENSE("GPL");
+
+/*
+ * The Macally ikey keyboard says that its logical and usage maximums are both
+ * 101, but the power key is 102 and the equals key is 103
+ */
+static const __u8 *macally_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+					unsigned int *rsize)
+{
+	if (*rsize >= 60 && rdesc[53] == 0x65 && rdesc[59] == 0x65) {
+		hid_info(hdev,
+			"fixing up Macally ikey keyboard report descriptor\n");
+		rdesc[53] = rdesc[59] = 0x67;
+	}
+	return rdesc;
+}
+
+static const struct hid_device_id macally_id_table[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_SOLID_YEAR,
+			 USB_DEVICE_ID_MACALLY_IKEY_KEYBOARD) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, macally_id_table);
+
+static struct hid_driver macally_driver = {
+	.name			= "macally",
+	.id_table		= macally_id_table,
+	.report_fixup		= macally_report_fixup,
+};
+
+module_hid_driver(macally_driver);