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, 86 insertions, 0 deletions

diff --git a/net/mac80211/led.h b/net/mac80211/led.h
new file mode 100644
index 000000000..d25f13346
--- /dev/null
+++ b/net/mac80211/led.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2006, Johannes Berg <johannes@sipsolutions.net>
+ */
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/leds.h>
+#include "ieee80211_i.h"
+
+#define MAC80211_BLINK_DELAY 50 /* ms */
+
+static inline void ieee80211_led_rx(struct ieee80211_local *local)
+{
+#ifdef CONFIG_MAC80211_LEDS
+	if (!atomic_read(&local->rx_led_active))
+		return;
+	led_trigger_blink_oneshot(&local->rx_led, MAC80211_BLINK_DELAY, MAC80211_BLINK_DELAY, 0);
+#endif
+}
+
+static inline void ieee80211_led_tx(struct ieee80211_local *local)
+{
+#ifdef CONFIG_MAC80211_LEDS
+	if (!atomic_read(&local->tx_led_active))
+		return;
+	led_trigger_blink_oneshot(&local->tx_led, MAC80211_BLINK_DELAY, MAC80211_BLINK_DELAY, 0);
+#endif
+}
+
+#ifdef CONFIG_MAC80211_LEDS
+void ieee80211_led_assoc(struct ieee80211_local *local,
+			 bool associated);
+void ieee80211_led_radio(struct ieee80211_local *local,
+			 bool enabled);
+void ieee80211_alloc_led_names(struct ieee80211_local *local);
+void ieee80211_free_led_names(struct ieee80211_local *local);
+void ieee80211_led_init(struct ieee80211_local *local);
+void ieee80211_led_exit(struct ieee80211_local *local);
+void ieee80211_mod_tpt_led_trig(struct ieee80211_local *local,
+				unsigned int types_on, unsigned int types_off);
+#else
+static inline void ieee80211_led_assoc(struct ieee80211_local *local,
+				       bool associated)
+{
+}
+static inline void ieee80211_led_radio(struct ieee80211_local *local,
+				       bool enabled)
+{
+}
+static inline void ieee80211_alloc_led_names(struct ieee80211_local *local)
+{
+}
+static inline void ieee80211_free_led_names(struct ieee80211_local *local)
+{
+}
+static inline void ieee80211_led_init(struct ieee80211_local *local)
+{
+}
+static inline void ieee80211_led_exit(struct ieee80211_local *local)
+{
+}
+static inline void ieee80211_mod_tpt_led_trig(struct ieee80211_local *local,
+					      unsigned int types_on,
+					      unsigned int types_off)
+{
+}
+#endif
+
+static inline void
+ieee80211_tpt_led_trig_tx(struct ieee80211_local *local, int bytes)
+{
+#ifdef CONFIG_MAC80211_LEDS
+	if (atomic_read(&local->tpt_led_active))
+		local->tpt_led_trigger->tx_bytes += bytes;
+#endif
+}
+
+static inline void
+ieee80211_tpt_led_trig_rx(struct ieee80211_local *local, int bytes)
+{
+#ifdef CONFIG_MAC80211_LEDS
+	if (atomic_read(&local->tpt_led_active))
+		local->tpt_led_trigger->rx_bytes += bytes;
+#endif
+}