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, 51 insertions, 0 deletions

diff --git a/include/video/cvisionppc.h b/include/video/cvisionppc.h
new file mode 100644
index 000000000..11250eee9
--- /dev/null
+++ b/include/video/cvisionppc.h
@@ -0,0 +1,51 @@
+/*
+ * Phase5 CybervisionPPC (TVP4020) definitions for the Permedia2 framebuffer
+ * driver.
+ *
+ * Copyright (c) 1998-1999 Ilario Nardinocchi (nardinoc@CS.UniBO.IT)
+ * --------------------------------------------------------------------------
+ * $Id: cvisionppc.h,v 1.8 1999/01/28 13:18:07 illo Exp $
+ * --------------------------------------------------------------------------
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#ifndef CVISIONPPC_H
+#define CVISIONPPC_H
+
+#ifndef PM2FB_H
+#include "pm2fb.h"
+#endif
+
+struct cvppc_par {
+	unsigned char* pci_config;
+	unsigned char* pci_bridge;
+	u32 user_flags;
+};
+
+#define CSPPC_PCI_BRIDGE		0xfffe0000
+#define CSPPC_BRIDGE_ENDIAN		0x0000
+#define CSPPC_BRIDGE_INT		0x0010
+
+#define	CVPPC_PCI_CONFIG		0xfffc0000
+#define CVPPC_ROM_ADDRESS		0xe2000001
+#define CVPPC_REGS_REGION		0xef000000
+#define CVPPC_FB_APERTURE_ONE		0xe0000000
+#define CVPPC_FB_APERTURE_TWO		0xe1000000
+#define CVPPC_FB_SIZE			0x00800000
+#define CVPPC_MEM_CONFIG_OLD		0xed61fcaa	/* FIXME Fujitsu?? */
+#define CVPPC_MEM_CONFIG_NEW		0xed41c532	/* FIXME USA?? */
+#define CVPPC_MEMCLOCK			83000		/* in KHz */
+
+/* CVPPC_BRIDGE_ENDIAN */
+#define CSPPCF_BRIDGE_BIG_ENDIAN	0x02
+
+/* CVPPC_BRIDGE_INT */
+#define CSPPCF_BRIDGE_ACTIVE_INT2	0x01
+
+#endif	/* CVISIONPPC_H */
+
+/*****************************************************************************
+ * That's all folks!
+ *****************************************************************************/