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, 71 insertions, 0 deletions

diff --git a/net/mac80211/Makefile b/net/mac80211/Makefile
new file mode 100644
index 000000000..36f1e3e22
--- /dev/null
+++ b/net/mac80211/Makefile
@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_MAC80211) += mac80211.o
+
+# mac80211 objects
+mac80211-y := \
+	main.o status.o \
+	driver-ops.o \
+	sta_info.o \
+	wep.o \
+	aead_api.o \
+	wpa.o \
+	scan.o offchannel.o \
+	ht.o agg-tx.o agg-rx.o \
+	vht.o \
+	he.o \
+	s1g.o \
+	ibss.o \
+	iface.o \
+	link.o \
+	rate.o \
+	tkip.o \
+	aes_cmac.o \
+	aes_gmac.o \
+	fils_aead.o \
+	cfg.o \
+	ethtool.o \
+	rx.o \
+	spectmgmt.o \
+	tx.o \
+	key.o \
+	util.o parse.o \
+	wme.o \
+	chan.o ap.o \
+	trace.o mlme.o \
+	tdls.o \
+	ocb.o \
+	airtime.o \
+	eht.o uhr.o nan.o
+
+mac80211-$(CONFIG_MAC80211_LEDS) += led.o
+mac80211-$(CONFIG_MAC80211_DEBUGFS) += \
+	debugfs.o \
+	debugfs_sta.o \
+	debugfs_netdev.o \
+	debugfs_key.o
+
+mac80211-$(CONFIG_MAC80211_MESH) += \
+	mesh.o \
+	mesh_pathtbl.o \
+	mesh_plink.o \
+	mesh_hwmp.o \
+	mesh_sync.o \
+	mesh_ps.o
+
+mac80211-$(CONFIG_PM) += pm.o
+
+CFLAGS_trace.o := -I$(src)
+
+rc80211_minstrel-y := \
+	rc80211_minstrel_ht.o
+
+rc80211_minstrel-$(CONFIG_MAC80211_DEBUGFS) += \
+	rc80211_minstrel_ht_debugfs.o
+
+mac80211-$(CONFIG_MAC80211_RC_MINSTREL) += $(rc80211_minstrel-y)
+
+obj-y += tests/
+
+mac80211-y += wbrf.o
+
+ccflags-y += -DDEBUG