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, 77 insertions, 0 deletions

diff --git a/net/Makefile b/net/Makefile
new file mode 100644
index 000000000..5b2dd7f07
--- /dev/null
+++ b/net/Makefile
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the linux networking.
+#
+# 2 Sep 2000, Christoph Hellwig <hch@infradead.org>
+# Rewritten to use lists instead of if-statements.
+#
+
+obj-y				:= devres.o socket.o core/
+
+obj-$(CONFIG_COMPAT)		+= compat.o
+
+# LLC has to be linked before the files in net/802/
+obj-$(CONFIG_LLC)		+= llc/
+obj-y				+= ethernet/ 802/ sched/ netlink/ bpf/ ethtool/
+obj-$(CONFIG_NETFILTER)		+= netfilter/
+obj-$(CONFIG_INET)		+= ipv4/
+obj-$(CONFIG_TLS)		+= tls/
+obj-$(CONFIG_XFRM)		+= xfrm/
+obj-$(CONFIG_UNIX)		+= unix/
+obj-$(CONFIG_INET_PSP)		+= psp/
+obj-y				+= ipv6/
+obj-$(CONFIG_PACKET)		+= packet/
+obj-$(CONFIG_NET_KEY)		+= key/
+obj-$(CONFIG_BRIDGE)		+= bridge/
+obj-$(CONFIG_NET_DEVLINK)	+= devlink/
+obj-y				+= dsa/
+obj-$(CONFIG_X25)		+= x25/
+obj-$(CONFIG_LAPB)		+= lapb/
+obj-$(CONFIG_CAN)		+= can/
+obj-$(CONFIG_BT)		+= bluetooth/
+obj-$(CONFIG_SUNRPC)		+= sunrpc/
+obj-$(CONFIG_AF_RXRPC)		+= rxrpc/
+obj-$(CONFIG_AF_KCM)		+= kcm/
+obj-$(CONFIG_STREAM_PARSER)	+= strparser/
+obj-$(CONFIG_ATM)		+= atm/
+obj-$(CONFIG_L2TP)		+= l2tp/
+obj-$(CONFIG_PHONET)		+= phonet/
+ifneq ($(CONFIG_VLAN_8021Q),)
+obj-y				+= 8021q/
+endif
+obj-$(CONFIG_IP_SCTP)		+= sctp/
+obj-$(CONFIG_RDS)		+= rds/
+obj-$(CONFIG_WIRELESS)		+= wireless/
+obj-$(CONFIG_MAC80211)		+= mac80211/
+obj-$(CONFIG_TIPC)		+= tipc/
+obj-$(CONFIG_NETLABEL)		+= netlabel/
+obj-$(CONFIG_IUCV)		+= iucv/
+obj-$(CONFIG_SMC)		+= smc/
+obj-$(CONFIG_RFKILL)		+= rfkill/
+obj-$(CONFIG_NET_9P)		+= 9p/
+obj-$(CONFIG_DCB)		+= dcb/
+obj-$(CONFIG_6LOWPAN)		+= 6lowpan/
+obj-$(CONFIG_IEEE802154)	+= ieee802154/
+obj-$(CONFIG_MAC802154)		+= mac802154/
+
+obj-$(CONFIG_SYSCTL)		+= sysctl_net.o
+obj-$(CONFIG_DNS_RESOLVER)	+= dns_resolver/
+obj-$(CONFIG_CEPH_LIB)		+= ceph/
+obj-$(CONFIG_BATMAN_ADV)	+= batman-adv/
+obj-$(CONFIG_NFC)		+= nfc/
+obj-$(CONFIG_PSAMPLE)		+= psample/
+obj-$(CONFIG_NET_IFE)		+= ife/
+obj-$(CONFIG_OPENVSWITCH)	+= openvswitch/
+obj-$(CONFIG_VSOCKETS)	+= vmw_vsock/
+obj-$(CONFIG_MPLS)		+= mpls/
+obj-$(CONFIG_NET_NSH)		+= nsh/
+obj-$(CONFIG_HSR)		+= hsr/
+obj-$(CONFIG_NET_SWITCHDEV)	+= switchdev/
+obj-$(CONFIG_NET_L3_MASTER_DEV)	+= l3mdev/
+obj-$(CONFIG_QRTR)		+= qrtr/
+obj-$(CONFIG_NET_NCSI)		+= ncsi/
+obj-$(CONFIG_XDP_SOCKETS)	+= xdp/
+obj-$(CONFIG_MPTCP)		+= mptcp/
+obj-$(CONFIG_MCTP)		+= mctp/
+obj-$(CONFIG_NET_HANDSHAKE)	+= handshake/
+obj-$(CONFIG_NET_SHAPER)	+= shaper/