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, 197 insertions, 0 deletions

diff --git a/drivers/video/fbdev/sunxvr1000.c b/drivers/video/fbdev/sunxvr1000.c
new file mode 100644
index 000000000..a93b06614
--- /dev/null
+++ b/drivers/video/fbdev/sunxvr1000.c
@@ -0,0 +1,197 @@
+/* sunxvr1000.c: Sun XVR-1000 fb driver for sparc64 systems
+ *
+ * License: GPL
+ *
+ * Copyright (C) 2010 David S. Miller (davem@davemloft.net)
+ */
+
+#include <linux/kernel.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+struct gfb_info {
+	struct fb_info		*info;
+
+	char __iomem		*fb_base;
+	unsigned long		fb_base_phys;
+
+	struct device_node	*of_node;
+
+	unsigned int		width;
+	unsigned int		height;
+	unsigned int		depth;
+	unsigned int		fb_size;
+
+	u32			pseudo_palette[16];
+};
+
+static int gfb_get_props(struct gfb_info *gp)
+{
+	gp->width = of_getintprop_default(gp->of_node, "width", 0);
+	gp->height = of_getintprop_default(gp->of_node, "height", 0);
+	gp->depth = of_getintprop_default(gp->of_node, "depth", 32);
+
+	if (!gp->width || !gp->height) {
+		printk(KERN_ERR "gfb: Critical properties missing for %pOF\n",
+		       gp->of_node);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int gfb_setcolreg(unsigned regno,
+			 unsigned red, unsigned green, unsigned blue,
+			 unsigned transp, struct fb_info *info)
+{
+	u32 value;
+
+	if (regno < 16) {
+		red >>= 8;
+		green >>= 8;
+		blue >>= 8;
+
+		value = (blue << 16) | (green << 8) | red;
+		((u32 *)info->pseudo_palette)[regno] = value;
+	}
+
+	return 0;
+}
+
+static const struct fb_ops gfb_ops = {
+	.owner			= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_setcolreg		= gfb_setcolreg,
+};
+
+static int gfb_set_fbinfo(struct gfb_info *gp)
+{
+	struct fb_info *info = gp->info;
+	struct fb_var_screeninfo *var = &info->var;
+
+	info->fbops = &gfb_ops;
+	info->screen_base = gp->fb_base;
+	info->screen_size = gp->fb_size;
+
+	info->pseudo_palette = gp->pseudo_palette;
+
+	/* Fill fix common fields */
+	strscpy(info->fix.id, "gfb", sizeof(info->fix.id));
+        info->fix.smem_start = gp->fb_base_phys;
+        info->fix.smem_len = gp->fb_size;
+        info->fix.type = FB_TYPE_PACKED_PIXELS;
+	if (gp->depth == 32 || gp->depth == 24)
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+	else
+		info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
+
+	var->xres = gp->width;
+	var->yres = gp->height;
+	var->xres_virtual = var->xres;
+	var->yres_virtual = var->yres;
+	var->bits_per_pixel = gp->depth;
+
+	var->red.offset = 0;
+	var->red.length = 8;
+	var->green.offset = 8;
+	var->green.length = 8;
+	var->blue.offset = 16;
+	var->blue.length = 8;
+	var->transp.offset = 0;
+	var->transp.length = 0;
+
+	if (fb_alloc_cmap(&info->cmap, 256, 0)) {
+		printk(KERN_ERR "gfb: Cannot allocate color map.\n");
+		return -ENOMEM;
+	}
+
+        return 0;
+}
+
+static int gfb_probe(struct platform_device *op)
+{
+	struct device_node *dp = op->dev.of_node;
+	struct fb_info *info;
+	struct gfb_info *gp;
+	int err;
+
+	info = framebuffer_alloc(sizeof(struct gfb_info), &op->dev);
+	if (!info) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	gp = info->par;
+	gp->info = info;
+	gp->of_node = dp;
+
+	gp->fb_base_phys = op->resource[6].start;
+
+	err = gfb_get_props(gp);
+	if (err)
+		goto err_release_fb;
+
+	/* Framebuffer length is the same regardless of resolution. */
+	info->fix.line_length = 16384;
+	gp->fb_size = info->fix.line_length * gp->height;
+
+	gp->fb_base = of_ioremap(&op->resource[6], 0,
+				 gp->fb_size, "gfb fb");
+	if (!gp->fb_base) {
+		err = -ENOMEM;
+		goto err_release_fb;
+	}
+
+	err = gfb_set_fbinfo(gp);
+	if (err)
+		goto err_unmap_fb;
+
+	printk("gfb: Found device at %pOF\n", dp);
+
+	err = register_framebuffer(info);
+	if (err < 0) {
+		printk(KERN_ERR "gfb: Could not register framebuffer %pOF\n",
+		       dp);
+		goto err_unmap_fb;
+	}
+
+	dev_set_drvdata(&op->dev, info);
+
+	return 0;
+
+err_unmap_fb:
+	of_iounmap(&op->resource[6], gp->fb_base, gp->fb_size);
+
+err_release_fb:
+        framebuffer_release(info);
+
+err_out:
+	return err;
+}
+
+static const struct of_device_id gfb_match[] = {
+	{
+		.name = "SUNW,gfb",
+	},
+	{},
+};
+
+static struct platform_driver gfb_driver = {
+	.probe		= gfb_probe,
+	.driver = {
+		.name			= "gfb",
+		.of_match_table		= gfb_match,
+		.suppress_bind_attrs	= true,
+	},
+};
+
+static int __init gfb_init(void)
+{
+	if (fb_get_options("gfb", NULL))
+		return -ENODEV;
+
+	return platform_driver_register(&gfb_driver);
+}
+device_initcall(gfb_init);