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, 99 insertions, 0 deletions

diff --git a/net/bluetooth/eir.h b/net/bluetooth/eir.h
new file mode 100644
index 000000000..9372db83f
--- /dev/null
+++ b/net/bluetooth/eir.h
@@ -0,0 +1,99 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BlueZ - Bluetooth protocol stack for Linux
+ *
+ * Copyright (C) 2021 Intel Corporation
+ */
+
+#include <linux/unaligned.h>
+
+void eir_create(struct hci_dev *hdev, u8 *data);
+
+u8 eir_create_adv_data(struct hci_dev *hdev, u8 instance, u8 *ptr, u8 size);
+u8 eir_create_scan_rsp(struct hci_dev *hdev, u8 instance, u8 *ptr);
+u8 eir_create_per_adv_data(struct hci_dev *hdev, u8 instance, u8 *ptr);
+
+u8 eir_append_local_name(struct hci_dev *hdev, u8 *eir, u8 ad_len);
+u8 eir_append_appearance(struct hci_dev *hdev, u8 *ptr, u8 ad_len);
+u8 eir_append_service_data(u8 *eir, u16 eir_len, u16 uuid, u8 *data,
+			   u8 data_len);
+
+static inline u16 eir_precalc_len(u8 data_len)
+{
+	return sizeof(u8) * 2 + data_len;
+}
+
+static inline u16 eir_append_data(u8 *eir, u16 eir_len, u8 type,
+				  u8 *data, u8 data_len)
+{
+	eir[eir_len++] = sizeof(type) + data_len;
+	eir[eir_len++] = type;
+	memcpy(&eir[eir_len], data, data_len);
+	eir_len += data_len;
+
+	return eir_len;
+}
+
+static inline u16 eir_append_le16(u8 *eir, u16 eir_len, u8 type, u16 data)
+{
+	eir[eir_len++] = sizeof(type) + sizeof(data);
+	eir[eir_len++] = type;
+	put_unaligned_le16(data, &eir[eir_len]);
+	eir_len += sizeof(data);
+
+	return eir_len;
+}
+
+static inline u16 eir_skb_put_data(struct sk_buff *skb, u8 type, u8 *data, u8 data_len)
+{
+	u8 *eir;
+	u16 eir_len;
+
+	eir_len	= eir_precalc_len(data_len);
+	eir = skb_put(skb, eir_len);
+	WARN_ON(sizeof(type) + data_len > U8_MAX);
+	eir[0] = sizeof(type) + data_len;
+	eir[1] = type;
+	memcpy(&eir[2], data, data_len);
+
+	return eir_len;
+}
+
+static inline void *eir_get_data(u8 *eir, size_t eir_len, u8 type,
+				 size_t *data_len)
+{
+	size_t parsed = 0;
+
+	if (eir_len < 2)
+		return NULL;
+
+	while (parsed < eir_len - 1) {
+		u8 field_len = eir[0];
+
+		if (field_len == 0)
+			break;
+
+		parsed += field_len + 1;
+
+		if (parsed > eir_len)
+			break;
+
+		if (eir[1] != type) {
+			eir += field_len + 1;
+			continue;
+		}
+
+		/* Zero length data */
+		if (field_len == 1)
+			return NULL;
+
+		if (data_len)
+			*data_len = field_len - 1;
+
+		return &eir[2];
+	}
+
+	return NULL;
+}
+
+void *eir_get_service_data(u8 *eir, size_t eir_len, u16 uuid, size_t *len);