From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001
From: Tim Chen <tim.c.chen@linux.intel.com>
Date: Mon, 21 Sep 2026 17:37:22 -0700
Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix
 LLC mis-scheduling bug

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
---
 drivers/video/console/sticon.c | 395 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 395 insertions(+)
 create mode 100644 drivers/video/console/sticon.c

(limited to 'drivers/video/console/sticon.c')

diff --git a/drivers/video/console/sticon.c b/drivers/video/console/sticon.c
new file mode 100644
index 000000000..6f58e6a9e
--- /dev/null
+++ b/drivers/video/console/sticon.c
@@ -0,0 +1,395 @@
+/*
+ *  linux/drivers/video/console/sticon.c - console driver using HP's STI firmware
+ *
+ *	Copyright (C) 2000 Philipp Rumpf <prumpf@tux.org>
+ *	Copyright (C) 2002-2020 Helge Deller <deller@gmx.de>
+ *
+ *  Based on linux/drivers/video/vgacon.c and linux/drivers/video/fbcon.c,
+ *  which were
+ *
+ *	Created 28 Sep 1997 by Geert Uytterhoeven
+ *	Rewritten by Martin Mares <mj@ucw.cz>, July 1998
+ *	Copyright (C) 1991, 1992  Linus Torvalds
+ *			    1995  Jay Estabrook
+ *	Copyright (C) 1995 Geert Uytterhoeven
+ *	Copyright (C) 1993 Bjoern Brauel
+ *			   Roman Hodek
+ *	Copyright (C) 1993 Hamish Macdonald
+ *			   Greg Harp
+ *	Copyright (C) 1994 David Carter [carter@compsci.bristol.ac.uk]
+ *
+ *	      with work by William Rucklidge (wjr@cs.cornell.edu)
+ *			   Geert Uytterhoeven
+ *			   Jes Sorensen (jds@kom.auc.dk)
+ *			   Martin Apel
+ *	      with work by Guenther Kelleter
+ *			   Martin Schaller
+ *			   Andreas Schwab
+ *			   Emmanuel Marty (core@ggi-project.org)
+ *			   Jakub Jelinek (jj@ultra.linux.cz)
+ *			   Martin Mares <mj@ucw.cz>
+ *
+ *  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.
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/errno.h>
+#include <linux/vt_kern.h>
+#include <linux/kd.h>
+#include <linux/selection.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/font.h>
+#include <linux/crc32.h>
+#include <linux/fb.h>
+
+#include <asm/io.h>
+
+#include <video/sticore.h>
+
+/* switching to graphics mode */
+#define BLANK 0
+static int vga_is_gfx;
+
+#define STI_DEF_FONT	sticon_sti->font
+
+/* borrowed from fbcon.c */
+#define FNTREFCOUNT(fd)	(fd->refcount)
+#define FNTCRC(fd)	(fd->crc)
+static struct sti_cooked_font *font_data[MAX_NR_CONSOLES];
+
+/* this is the sti_struct used for this console */
+static struct sti_struct *sticon_sti;
+
+static const char *sticon_startup(void)
+{
+    return "STI console";
+}
+
+static void sticon_putcs(struct vc_data *conp, const u16 *s, unsigned int count,
+			 unsigned int ypos, unsigned int xpos)
+{
+    if (vga_is_gfx || console_blanked)
+	    return;
+
+    if (conp->vc_mode != KD_TEXT)
+    	    return;
+
+    while (count--) {
+	sti_putc(sticon_sti, scr_readw(s++), ypos, xpos++,
+		 font_data[conp->vc_num]);
+    }
+}
+
+static void sticon_cursor(struct vc_data *conp, bool enable)
+{
+    unsigned short car1;
+
+    /* no cursor update if screen is blanked */
+    if (vga_is_gfx || console_blanked)
+	return;
+
+    car1 = conp->vc_screenbuf[conp->state.x + conp->state.y * conp->vc_cols];
+    if (!enable) {
+	sti_putc(sticon_sti, car1, conp->state.y, conp->state.x,
+		 font_data[conp->vc_num]);
+	return;
+    }
+
+    switch (CUR_SIZE(conp->vc_cursor_type)) {
+    case CUR_UNDERLINE:
+    case CUR_LOWER_THIRD:
+    case CUR_LOWER_HALF:
+    case CUR_TWO_THIRDS:
+    case CUR_BLOCK:
+	sti_putc(sticon_sti, (car1 & 255) + (0 << 8) + (7 << 11),
+		 conp->state.y, conp->state.x, font_data[conp->vc_num]);
+	break;
+    }
+}
+
+static bool sticon_scroll(struct vc_data *conp, unsigned int t,
+		unsigned int b, enum con_scroll dir, unsigned int count)
+{
+    struct sti_struct *sti = sticon_sti;
+
+    if (vga_is_gfx)
+        return false;
+
+    sticon_cursor(conp, false);
+
+    switch (dir) {
+    case SM_UP:
+	sti_bmove(sti, t + count, 0, t, 0, b - t - count, conp->vc_cols,
+		  font_data[conp->vc_num]);
+	sti_clear(sti, b - count, 0, count, conp->vc_cols,
+		  conp->vc_video_erase_char, font_data[conp->vc_num]);
+	break;
+
+    case SM_DOWN:
+	sti_bmove(sti, t, 0, t + count, 0, b - t - count, conp->vc_cols,
+		  font_data[conp->vc_num]);
+	sti_clear(sti, t, 0, count, conp->vc_cols,
+		  conp->vc_video_erase_char, font_data[conp->vc_num]);
+	break;
+    }
+
+    return false;
+}
+
+static void sticon_set_def_font(int unit)
+{
+	if (font_data[unit] != STI_DEF_FONT) {
+		if (--FNTREFCOUNT(font_data[unit]) == 0) {
+			kfree(font_data[unit]->raw_ptr);
+			kfree(font_data[unit]);
+		}
+		font_data[unit] = STI_DEF_FONT;
+	}
+}
+
+static int sticon_set_font(struct vc_data *vc, const struct console_font *op,
+			   unsigned int vpitch)
+{
+	struct sti_struct *sti = sticon_sti;
+	int vc_cols, vc_rows, vc_old_cols, vc_old_rows;
+	int unit = vc->vc_num;
+	int w = op->width;
+	int h = op->height;
+	int size, i, bpc, pitch;
+	struct sti_rom_font *new_font;
+	struct sti_cooked_font *cooked_font;
+	unsigned char *data = op->data, *p;
+
+	if ((w < 6) || (h < 6) || (w > 32) || (h > 32) || (vpitch != 32)
+	    || (op->charcount != 256 && op->charcount != 512))
+		return -EINVAL;
+	pitch = ALIGN(w, 8) / 8;
+	bpc = pitch * h;
+	size = bpc * op->charcount;
+
+	new_font = kmalloc(sizeof(*new_font) + size, STI_LOWMEM);
+	if (!new_font)
+		return -ENOMEM;
+
+	new_font->first_char = 0;
+	new_font->last_char = op->charcount - 1;
+	new_font->width = w;
+	new_font->height = h;
+	new_font->font_type = STI_FONT_HPROMAN8;
+	new_font->bytes_per_char = bpc;
+	new_font->underline_height = 0;
+	new_font->underline_pos = 0;
+
+	cooked_font = kzalloc_obj(*cooked_font);
+	if (!cooked_font) {
+		kfree(new_font);
+		return -ENOMEM;
+	}
+	cooked_font->raw = new_font;
+	cooked_font->raw_ptr = new_font;
+	cooked_font->width = w;
+	cooked_font->height = h;
+	FNTREFCOUNT(cooked_font) = 0;	/* usage counter */
+
+	p = (unsigned char *) new_font;
+	p += sizeof(*new_font);
+	for (i = 0; i < op->charcount; i++) {
+		memcpy(p, data, bpc);
+		data += pitch*32;
+		p += bpc;
+	}
+	FNTCRC(cooked_font) = crc32(0, new_font, size + sizeof(*new_font));
+	sti_font_convert_bytemode(sti, cooked_font);
+	new_font = cooked_font->raw_ptr;
+
+	/* check if font is already used by other console */
+	for (i = 0; i < MAX_NR_CONSOLES; i++) {
+		if (font_data[i] != STI_DEF_FONT
+		    && (FNTCRC(font_data[i]) == FNTCRC(cooked_font))) {
+			kfree(new_font);
+			kfree(cooked_font);
+			/* current font is the same as the new one */
+			if (i == unit)
+				return 0;
+			cooked_font = font_data[i];
+			new_font = cooked_font->raw_ptr;
+			break;
+		}
+	}
+
+	/* clear screen with old font: we now may have less rows */
+	vc_old_rows = vc->vc_rows;
+	vc_old_cols = vc->vc_cols;
+	sti_clear(sticon_sti, 0, 0, vc_old_rows, vc_old_cols,
+		  vc->vc_video_erase_char, font_data[vc->vc_num]);
+
+	/* delete old font in case it is a user font */
+	sticon_set_def_font(unit);
+
+	FNTREFCOUNT(cooked_font)++;
+	font_data[unit] = cooked_font;
+
+	vc_cols = sti_onscreen_x(sti) / cooked_font->width;
+	vc_rows = sti_onscreen_y(sti) / cooked_font->height;
+	vc_resize(vc, vc_cols, vc_rows);
+
+	/* need to repaint screen if cols & rows are same as old font */
+	if (vc_cols == vc_old_cols && vc_rows == vc_old_rows)
+		update_screen(vc);
+
+	return 0;
+}
+
+static int sticon_font_default(struct vc_data *vc, struct console_font *op,
+			       const char *name)
+{
+	sticon_set_def_font(vc->vc_num);
+
+	return 0;
+}
+
+static int sticon_font_set(struct vc_data *vc, const struct console_font *font,
+			   unsigned int vpitch, unsigned int flags)
+{
+	return sticon_set_font(vc, font, vpitch);
+}
+
+static void sticon_init(struct vc_data *c, bool init)
+{
+    struct sti_struct *sti = sticon_sti;
+    int vc_cols, vc_rows;
+
+    sti_set(sti, 0, 0, sti_onscreen_y(sti), sti_onscreen_x(sti), 0);
+    vc_cols = sti_onscreen_x(sti) / sti->font->width;
+    vc_rows = sti_onscreen_y(sti) / sti->font->height;
+    c->vc_can_do_color = 1;
+
+    if (init) {
+	c->vc_cols = vc_cols;
+	c->vc_rows = vc_rows;
+    } else {
+	vc_resize(c, vc_cols, vc_rows);
+    }
+}
+
+static void sticon_deinit(struct vc_data *c)
+{
+    int i;
+
+    /* free memory used by user font */
+    for (i = 0; i < MAX_NR_CONSOLES; i++)
+	sticon_set_def_font(i);
+}
+
+static void sticon_clear(struct vc_data *conp, unsigned int sy, unsigned int sx,
+			 unsigned int width)
+{
+    sti_clear(sticon_sti, sy, sx, 1, width,
+	      conp->vc_video_erase_char, font_data[conp->vc_num]);
+}
+
+static bool sticon_switch(struct vc_data *conp)
+{
+    return true;	/* needs refreshing */
+}
+
+static bool sticon_blank(struct vc_data *c, enum vesa_blank_mode blank,
+			 bool mode_switch)
+{
+    if (blank == VESA_NO_BLANKING) {
+	if (mode_switch)
+	    vga_is_gfx = 0;
+	return true;
+    }
+    sti_clear(sticon_sti, 0, 0, c->vc_rows, c->vc_cols, BLANK,
+	      font_data[c->vc_num]);
+    if (mode_switch)
+	vga_is_gfx = 1;
+
+    return true;
+}
+
+static u8 sticon_build_attr(struct vc_data *conp, u8 color,
+			    enum vc_intensity intens,
+			    bool blink, bool underline, bool reverse,
+			    bool italic)
+{
+	u8 fg = color & 7;
+	u8 bg = (color & 0x70) >> 4;
+
+	if (reverse)
+		return (fg << 3) | bg;
+	else
+		return (bg << 3) | fg;
+}
+
+static void sticon_invert_region(struct vc_data *conp, u16 *p, int count)
+{
+    int col = 1; /* vga_can_do_color; */
+
+    while (count--) {
+	u16 a = scr_readw(p);
+
+	if (col)
+		a = ((a) & 0x88ff) | (((a) & 0x7000) >> 4) | (((a) & 0x0700) << 4);
+	else
+		a = ((a & 0x0700) == 0x0100) ? 0x7000 : 0x7700;
+
+	scr_writew(a, p++);
+    }
+}
+
+static const struct consw sti_con = {
+	.owner			= THIS_MODULE,
+	.con_startup		= sticon_startup,
+	.con_init		= sticon_init,
+	.con_deinit		= sticon_deinit,
+	.con_clear		= sticon_clear,
+	.con_putcs		= sticon_putcs,
+	.con_cursor		= sticon_cursor,
+	.con_scroll		= sticon_scroll,
+	.con_switch		= sticon_switch,
+	.con_blank		= sticon_blank,
+	.con_font_set		= sticon_font_set,
+	.con_font_default	= sticon_font_default,
+	.con_build_attr		= sticon_build_attr,
+	.con_invert_region	= sticon_invert_region,
+};
+
+
+
+static int __init sticonsole_init(void)
+{
+    int err, i;
+
+    /* already initialized ? */
+    if (sticon_sti)
+	 return 0;
+
+    sticon_sti = sti_get_rom(0);
+    if (!sticon_sti)
+	return -ENODEV;
+
+    for (i = 0; i < MAX_NR_CONSOLES; i++)
+	font_data[i] = STI_DEF_FONT;
+
+    pr_info("sticon: Initializing STI text console on %s at [%s]\n",
+	sticon_sti->sti_data->inq_outptr.dev_name,
+	sticon_sti->pa_path);
+    console_lock();
+    err = do_take_over_console(&sti_con, 0, MAX_NR_CONSOLES - 1,
+		PAGE0->mem_cons.cl_class != CL_DUPLEX);
+    console_unlock();
+
+    return err;
+}
+
+module_init(sticonsole_init);
+MODULE_DESCRIPTION("HP STI console driver");
+MODULE_LICENSE("GPL");
-- 
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