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, 71 insertions, 0 deletions

diff --git a/drivers/video/fbdev/macmodes.h b/drivers/video/fbdev/macmodes.h
new file mode 100644
index 000000000..b86ba08aa
--- /dev/null
+++ b/drivers/video/fbdev/macmodes.h
@@ -0,0 +1,71 @@
+/*
+ *  linux/drivers/video/macmodes.h -- Standard MacOS video modes
+ *
+ *	Copyright (C) 1998 Geert Uytterhoeven
+ *
+ *  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 _VIDEO_MACMODES_H
+#define _VIDEO_MACMODES_H
+
+    /*
+     *  Video mode values.
+     *  These are supposed to be the same as the values that Apple uses in
+     *  MacOS.
+     */
+
+#define VMODE_NVRAM		0
+#define VMODE_512_384_60I	1	/* 512x384, 60Hz interlaced (NTSC) */
+#define VMODE_512_384_60	2	/* 512x384, 60Hz */
+#define VMODE_640_480_50I	3	/* 640x480, 50Hz interlaced (PAL) */
+#define VMODE_640_480_60I	4	/* 640x480, 60Hz interlaced (NTSC) */
+#define VMODE_640_480_60	5	/* 640x480, 60Hz (VGA) */
+#define VMODE_640_480_67	6	/* 640x480, 67Hz */
+#define VMODE_640_870_75P	7	/* 640x870, 75Hz (portrait) */
+#define VMODE_768_576_50I	8	/* 768x576, 50Hz (PAL full frame) */
+#define VMODE_800_600_56	9	/* 800x600, 56Hz */
+#define VMODE_800_600_60	10	/* 800x600, 60Hz */
+#define VMODE_800_600_72	11	/* 800x600, 72Hz */
+#define VMODE_800_600_75	12	/* 800x600, 75Hz */
+#define VMODE_832_624_75	13	/* 832x624, 75Hz */
+#define VMODE_1024_768_60	14	/* 1024x768, 60Hz */
+#define VMODE_1024_768_70	15	/* 1024x768, 70Hz (or 72Hz?) */
+#define VMODE_1024_768_75V	16	/* 1024x768, 75Hz (VESA) */
+#define VMODE_1024_768_75	17	/* 1024x768, 75Hz */
+#define VMODE_1152_870_75	18	/* 1152x870, 75Hz */
+#define VMODE_1280_960_75	19	/* 1280x960, 75Hz */
+#define VMODE_1280_1024_75	20	/* 1280x1024, 75Hz */
+#define VMODE_1152_768_60	21	/* 1152x768, 60Hz     Titanium PowerBook */
+#define VMODE_1600_1024_60	22	/* 1600x1024, 60Hz 22" Cinema Display */
+#define VMODE_MAX		22
+#define VMODE_CHOOSE		99
+
+#define CMODE_NVRAM		-1
+#define CMODE_CHOOSE		-2
+#define CMODE_8			0	/* 8 bits/pixel */
+#define CMODE_16		1	/* 16 (actually 15) bits/pixel */
+#define CMODE_32		2	/* 32 (actually 24) bits/pixel */
+
+
+extern int mac_vmode_to_var(int vmode, int cmode,
+			    struct fb_var_screeninfo *var);
+extern int mac_var_to_vmode(const struct fb_var_screeninfo *var, int *vmode,
+			    int *cmode);
+extern int mac_map_monitor_sense(int sense);
+extern int mac_find_mode(struct fb_var_screeninfo *var,
+			 struct fb_info *info,
+			 const char *mode_option,
+			 unsigned int default_bpp);
+
+
+    /*
+     *  Addresses in NVRAM where video mode and pixel size are stored.
+     */
+
+#define NV_VMODE		0x140f
+#define NV_CMODE		0x1410
+
+#endif /* _VIDEO_MACMODES_H */