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, 85 insertions, 0 deletions

diff --git a/net/sched/Makefile b/net/sched/Makefile
new file mode 100644
index 000000000..5078ea84e
--- /dev/null
+++ b/net/sched/Makefile
@@ -0,0 +1,85 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the Linux Traffic Control Unit.
+#
+
+obj-y	:= sch_generic.o sch_mq.o
+
+obj-$(CONFIG_INET)		+= sch_frag.o
+obj-$(CONFIG_NET_SCHED)		+= sch_api.o sch_blackhole.o
+obj-$(CONFIG_NET_CLS)		+= cls_api.o
+obj-$(CONFIG_NET_CLS_ACT)	+= act_api.o
+obj-$(CONFIG_NET_ACT_POLICE)	+= act_police.o
+obj-$(CONFIG_NET_ACT_GACT)	+= act_gact.o
+obj-$(CONFIG_NET_ACT_MIRRED)	+= act_mirred.o
+obj-$(CONFIG_NET_ACT_SAMPLE)	+= act_sample.o
+obj-$(CONFIG_NET_ACT_NAT)	+= act_nat.o
+obj-$(CONFIG_NET_ACT_PEDIT)	+= act_pedit.o
+obj-$(CONFIG_NET_ACT_SIMP)	+= act_simple.o
+obj-$(CONFIG_NET_ACT_SKBEDIT)	+= act_skbedit.o
+obj-$(CONFIG_NET_ACT_CSUM)	+= act_csum.o
+obj-$(CONFIG_NET_ACT_MPLS)	+= act_mpls.o
+obj-$(CONFIG_NET_ACT_VLAN)	+= act_vlan.o
+obj-$(CONFIG_NET_ACT_BPF)	+= act_bpf.o
+obj-$(CONFIG_NET_ACT_CONNMARK)	+= act_connmark.o
+obj-$(CONFIG_NET_ACT_CTINFO)	+= act_ctinfo.o
+obj-$(CONFIG_NET_ACT_SKBMOD)	+= act_skbmod.o
+obj-$(CONFIG_NET_ACT_IFE)	+= act_ife.o
+obj-$(CONFIG_NET_IFE_SKBMARK)	+= act_meta_mark.o
+obj-$(CONFIG_NET_IFE_SKBPRIO)	+= act_meta_skbprio.o
+obj-$(CONFIG_NET_IFE_SKBTCINDEX)	+= act_meta_skbtcindex.o
+obj-$(CONFIG_NET_ACT_TUNNEL_KEY)+= act_tunnel_key.o
+obj-$(CONFIG_NET_ACT_CT)	+= act_ct.o
+obj-$(CONFIG_NET_ACT_GATE)	+= act_gate.o
+obj-$(CONFIG_NET_SCH_FIFO)	+= sch_fifo.o
+obj-$(CONFIG_NET_SCH_HTB)	+= sch_htb.o
+obj-$(CONFIG_NET_SCH_HFSC)	+= sch_hfsc.o
+obj-$(CONFIG_NET_SCH_RED)	+= sch_red.o
+obj-$(CONFIG_NET_SCH_GRED)	+= sch_gred.o
+obj-$(CONFIG_NET_SCH_INGRESS)	+= sch_ingress.o
+obj-$(CONFIG_NET_SCH_SFB)	+= sch_sfb.o
+obj-$(CONFIG_NET_SCH_SFQ)	+= sch_sfq.o
+obj-$(CONFIG_NET_SCH_TBF)	+= sch_tbf.o
+obj-$(CONFIG_NET_SCH_TEQL)	+= sch_teql.o
+obj-$(CONFIG_NET_SCH_PRIO)	+= sch_prio.o
+obj-$(CONFIG_NET_SCH_MULTIQ)	+= sch_multiq.o
+obj-$(CONFIG_NET_SCH_NETEM)	+= sch_netem.o
+obj-$(CONFIG_NET_SCH_DRR)	+= sch_drr.o
+obj-$(CONFIG_NET_SCH_PLUG)	+= sch_plug.o
+obj-$(CONFIG_NET_SCH_ETS)	+= sch_ets.o
+obj-$(CONFIG_NET_SCH_MQPRIO)	+= sch_mqprio.o
+obj-$(CONFIG_NET_SCH_MQPRIO_LIB) += sch_mqprio_lib.o
+obj-$(CONFIG_NET_SCH_SKBPRIO)	+= sch_skbprio.o
+obj-$(CONFIG_NET_SCH_CHOKE)	+= sch_choke.o
+obj-$(CONFIG_NET_SCH_QFQ)	+= sch_qfq.o
+obj-$(CONFIG_NET_SCH_CODEL)	+= sch_codel.o
+obj-$(CONFIG_NET_SCH_FQ_CODEL)	+= sch_fq_codel.o
+obj-$(CONFIG_NET_SCH_CAKE)	+= sch_cake.o
+obj-$(CONFIG_NET_SCH_FQ)	+= sch_fq.o
+obj-$(CONFIG_NET_SCH_HHF)	+= sch_hhf.o
+obj-$(CONFIG_NET_SCH_PIE)	+= sch_pie.o
+obj-$(CONFIG_NET_SCH_FQ_PIE)	+= sch_fq_pie.o
+obj-$(CONFIG_NET_SCH_CBS)	+= sch_cbs.o
+obj-$(CONFIG_NET_SCH_ETF)	+= sch_etf.o
+obj-$(CONFIG_NET_SCH_TAPRIO)	+= sch_taprio.o
+obj-$(CONFIG_NET_SCH_BPF)	+= bpf_qdisc.o
+obj-$(CONFIG_NET_SCH_DUALPI2)	+= sch_dualpi2.o
+
+obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
+obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o
+obj-$(CONFIG_NET_CLS_FW)	+= cls_fw.o
+obj-$(CONFIG_NET_CLS_BASIC)	+= cls_basic.o
+obj-$(CONFIG_NET_CLS_FLOW)	+= cls_flow.o
+obj-$(CONFIG_NET_CLS_CGROUP)	+= cls_cgroup.o
+obj-$(CONFIG_NET_CLS_BPF)	+= cls_bpf.o
+obj-$(CONFIG_NET_CLS_FLOWER)	+= cls_flower.o
+obj-$(CONFIG_NET_CLS_MATCHALL)	+= cls_matchall.o
+obj-$(CONFIG_NET_EMATCH)	+= ematch.o
+obj-$(CONFIG_NET_EMATCH_CMP)	+= em_cmp.o
+obj-$(CONFIG_NET_EMATCH_NBYTE)	+= em_nbyte.o
+obj-$(CONFIG_NET_EMATCH_U32)	+= em_u32.o
+obj-$(CONFIG_NET_EMATCH_META)	+= em_meta.o
+obj-$(CONFIG_NET_EMATCH_TEXT)	+= em_text.o
+obj-$(CONFIG_NET_EMATCH_CANID)	+= em_canid.o
+obj-$(CONFIG_NET_EMATCH_IPSET)	+= em_ipset.o
+obj-$(CONFIG_NET_EMATCH_IPT)	+= em_ipt.o