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, 36 insertions, 0 deletions

diff --git a/drivers/scsi/lpfc/Makefile b/drivers/scsi/lpfc/Makefile
new file mode 100644
index 000000000..bbd1faf41
--- /dev/null
+++ b/drivers/scsi/lpfc/Makefile
@@ -0,0 +1,36 @@
+#/*******************************************************************
+# * This file is part of the Emulex Linux Device Driver for         *
+# * Fibre Channel Host Bus Adapters.                                *
+# * Copyright (C) 2017-2018 Broadcom. All Rights Reserved. The term *
+# * “Broadcom” refers to Broadcom Inc. and/or its subsidiaries.     *
+# * Copyright (C) 2004-2012 Emulex.  All rights reserved.           *
+# * EMULEX and SLI are trademarks of Emulex.                        *
+# * www.broadcom.com                                                *
+# *                                                                 *
+# * This program is free software; you can redistribute it and/or   *
+# * modify it under the terms of version 2 of the GNU General       *
+# * Public License as published by the Free Software Foundation.    *
+# * This program is distributed in the hope that it will be useful. *
+# * ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND          *
+# * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY,  *
+# * FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT, ARE      *
+# * DISCLAIMED, EXCEPT TO THE EXTENT THAT SUCH DISCLAIMERS ARE HELD *
+# * TO BE LEGALLY INVALID.  See the GNU General Public License for  *
+# * more details, a copy of which can be found in the file COPYING  *
+# * included with this package.                                     *
+# *******************************************************************/
+######################################################################
+
+ccflags-$(GCOV) := -fprofile-arcs -ftest-coverage
+ccflags-$(GCOV) += -O0
+
+ifdef WARNINGS_BECOME_ERRORS
+ccflags-y += -Werror
+endif
+
+obj-$(CONFIG_SCSI_LPFC) := lpfc.o
+
+lpfc-objs := lpfc_mem.o lpfc_sli.o lpfc_ct.o lpfc_els.o \
+	lpfc_hbadisc.o	lpfc_init.o lpfc_mbox.o lpfc_nportdisc.o   \
+	lpfc_scsi.o lpfc_attr.o lpfc_vport.o lpfc_debugfs.o lpfc_bsg.o \
+	lpfc_nvme.o lpfc_nvmet.o lpfc_vmid.o