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, 177 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-grlib.c b/drivers/usb/host/ehci-grlib.c
new file mode 100644
index 000000000..bd9762eaa
--- /dev/null
+++ b/drivers/usb/host/ehci-grlib.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for Aeroflex Gaisler GRLIB GRUSBHC EHCI host controller
+ *
+ * GRUSBHC is typically found on LEON/GRLIB SoCs
+ *
+ * (c) Jan Andersson <jan@gaisler.com>
+ *
+ * Based on ehci-ppc-of.c which is:
+ * (c) Valentine Barshak <vbarshak@ru.mvista.com>
+ * and in turn based on "ehci-ppc-soc.c" by Stefan Roese <sr@denx.de>
+ * and "ohci-ppc-of.c" by Sylvain Munaut <tnt@246tNt.com>
+ */
+
+#include <linux/err.h>
+#include <linux/signal.h>
+
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+
+#define GRUSBHC_HCIVERSION 0x0100 /* Known value of cap. reg. HCIVERSION */
+
+static const struct hc_driver ehci_grlib_hc_driver = {
+	.description		= hcd_name,
+	.product_desc		= "GRLIB GRUSBHC EHCI",
+	.hcd_priv_size		= sizeof(struct ehci_hcd),
+
+	/*
+	 * generic hardware linkage
+	 */
+	.irq			= ehci_irq,
+	.flags			= HCD_MEMORY | HCD_DMA | HCD_USB2 | HCD_BH,
+
+	/*
+	 * basic lifecycle operations
+	 */
+	.reset			= ehci_setup,
+	.start			= ehci_run,
+	.stop			= ehci_stop,
+	.shutdown		= ehci_shutdown,
+
+	/*
+	 * managing i/o requests and associated device resources
+	 */
+	.urb_enqueue		= ehci_urb_enqueue,
+	.urb_dequeue		= ehci_urb_dequeue,
+	.endpoint_disable	= ehci_endpoint_disable,
+	.endpoint_reset		= ehci_endpoint_reset,
+
+	/*
+	 * scheduling support
+	 */
+	.get_frame_number	= ehci_get_frame,
+
+	/*
+	 * root hub support
+	 */
+	.hub_status_data	= ehci_hub_status_data,
+	.hub_control		= ehci_hub_control,
+#ifdef	CONFIG_PM
+	.bus_suspend		= ehci_bus_suspend,
+	.bus_resume		= ehci_bus_resume,
+#endif
+	.relinquish_port	= ehci_relinquish_port,
+	.port_handed_over	= ehci_port_handed_over,
+
+	.clear_tt_buffer_complete	= ehci_clear_tt_buffer_complete,
+};
+
+
+static int ehci_hcd_grlib_probe(struct platform_device *op)
+{
+	struct device_node *dn = op->dev.of_node;
+	struct usb_hcd *hcd;
+	struct ehci_hcd	*ehci = NULL;
+	struct resource res;
+	u32 hc_capbase;
+	int irq;
+	int rv;
+
+	if (usb_disabled())
+		return -ENODEV;
+
+	dev_dbg(&op->dev, "initializing GRUSBHC EHCI USB Controller\n");
+
+	rv = of_address_to_resource(dn, 0, &res);
+	if (rv)
+		return rv;
+
+	/* usb_create_hcd requires dma_mask != NULL */
+	op->dev.dma_mask = &op->dev.coherent_dma_mask;
+	hcd = usb_create_hcd(&ehci_grlib_hc_driver, &op->dev,
+			"GRUSBHC EHCI USB");
+	if (!hcd)
+		return -ENOMEM;
+
+	hcd->rsrc_start = res.start;
+	hcd->rsrc_len = resource_size(&res);
+
+	irq = irq_of_parse_and_map(dn, 0);
+	if (!irq) {
+		dev_err(&op->dev, "%s: irq_of_parse_and_map failed\n",
+			__FILE__);
+		rv = -EBUSY;
+		goto err_irq;
+	}
+
+	hcd->regs = devm_ioremap_resource(&op->dev, &res);
+	if (IS_ERR(hcd->regs)) {
+		rv = PTR_ERR(hcd->regs);
+		goto err_ioremap;
+	}
+
+	ehci = hcd_to_ehci(hcd);
+
+	ehci->caps = hcd->regs;
+
+	/* determine endianness of this implementation */
+	hc_capbase = ehci_readl(ehci, &ehci->caps->hc_capbase);
+	if (HC_VERSION(ehci, hc_capbase) != GRUSBHC_HCIVERSION) {
+		ehci->big_endian_mmio = 1;
+		ehci->big_endian_desc = 1;
+		ehci->big_endian_capbase = 1;
+	}
+
+	rv = usb_add_hcd(hcd, irq, 0);
+	if (rv)
+		goto err_ioremap;
+
+	device_wakeup_enable(hcd->self.controller);
+	return 0;
+
+err_ioremap:
+	irq_dispose_mapping(irq);
+err_irq:
+	usb_put_hcd(hcd);
+
+	return rv;
+}
+
+
+static void ehci_hcd_grlib_remove(struct platform_device *op)
+{
+	struct usb_hcd *hcd = platform_get_drvdata(op);
+
+	dev_dbg(&op->dev, "stopping GRLIB GRUSBHC EHCI USB Controller\n");
+
+	usb_remove_hcd(hcd);
+
+	irq_dispose_mapping(hcd->irq);
+
+	usb_put_hcd(hcd);
+}
+
+
+static const struct of_device_id ehci_hcd_grlib_of_match[] = {
+	{
+		.name = "GAISLER_EHCI",
+	 },
+	{
+		.name = "01_026",
+	 },
+	{},
+};
+MODULE_DEVICE_TABLE(of, ehci_hcd_grlib_of_match);
+
+
+static struct platform_driver ehci_grlib_driver = {
+	.probe		= ehci_hcd_grlib_probe,
+	.remove		= ehci_hcd_grlib_remove,
+	.shutdown	= usb_hcd_platform_shutdown,
+	.driver = {
+		.name = "grlib-ehci",
+		.of_match_table = ehci_hcd_grlib_of_match,
+	},
+};