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, 49 insertions, 0 deletions

diff --git a/net/rxrpc/Makefile b/net/rxrpc/Makefile
new file mode 100644
index 000000000..f994f9f30
--- /dev/null
+++ b/net/rxrpc/Makefile
@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for Linux kernel RxRPC
+#
+
+obj-$(CONFIG_AF_RXRPC) += rxrpc.o
+
+rxrpc-y := \
+	af_rxrpc.o \
+	call_accept.o \
+	call_event.o \
+	call_object.o \
+	call_state.o \
+	conn_client.o \
+	conn_event.o \
+	conn_object.o \
+	conn_service.o \
+	input.o \
+	input_rack.o \
+	insecure.o \
+	io_thread.o \
+	key.o \
+	local_event.o \
+	local_object.o \
+	misc.o \
+	net_ns.o \
+	oob.o \
+	output.o \
+	peer_event.o \
+	peer_object.o \
+	recvmsg.o \
+	rtt.o \
+	security.o \
+	sendmsg.o \
+	server_key.o \
+	skbuff.o \
+	txbuf.o \
+	utils.o
+
+rxrpc-$(CONFIG_PROC_FS) += proc.o
+rxrpc-$(CONFIG_RXKAD) += rxkad.o fcrypt.o
+rxrpc-$(CONFIG_SYSCTL) += sysctl.o
+rxrpc-$(CONFIG_RXGK) += \
+	rxgk.o \
+	rxgk_app.o \
+	rxgk_kdf.o
+
+obj-$(CONFIG_RXPERF) += rxperf.o
+obj-$(CONFIG_KUNIT) += tests/