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, 152 insertions, 0 deletions

diff --git a/drivers/usb/misc/ezusb.c b/drivers/usb/misc/ezusb.c
new file mode 100644
index 000000000..7ab4856ab
--- /dev/null
+++ b/drivers/usb/misc/ezusb.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * EZ-USB specific functions used by some of the USB to Serial drivers.
+ *
+ * Copyright (C) 1999 - 2002 Greg Kroah-Hartman (greg@kroah.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/firmware.h>
+#include <linux/ihex.h>
+#include <linux/usb/ezusb.h>
+
+struct ezusb_fx_type {
+	/* EZ-USB Control and Status Register.  Bit 0 controls 8051 reset */
+	unsigned short cpucs_reg;
+	unsigned short max_internal_adress;
+};
+
+static const struct ezusb_fx_type ezusb_fx1 = {
+	.cpucs_reg = 0x7F92,
+	.max_internal_adress = 0x1B3F,
+};
+
+/* Commands for writing to memory */
+#define WRITE_INT_RAM 0xA0
+#define WRITE_EXT_RAM 0xA3
+
+static int ezusb_writememory(struct usb_device *dev, int address,
+				unsigned char *data, int length, __u8 request)
+{
+	if (!dev)
+		return -ENODEV;
+
+	return usb_control_msg_send(dev, 0, request,
+				 USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
+				 address, 0, data, length, 3000, GFP_KERNEL);
+}
+
+static int ezusb_set_reset(struct usb_device *dev, unsigned short cpucs_reg,
+			   unsigned char reset_bit)
+{
+	int response = ezusb_writememory(dev, cpucs_reg, &reset_bit, 1, WRITE_INT_RAM);
+	if (response < 0)
+		dev_err(&dev->dev, "%s-%d failed: %d\n",
+						__func__, reset_bit, response);
+	return response;
+}
+
+int ezusb_fx1_set_reset(struct usb_device *dev, unsigned char reset_bit)
+{
+	return ezusb_set_reset(dev, ezusb_fx1.cpucs_reg, reset_bit);
+}
+EXPORT_SYMBOL_GPL(ezusb_fx1_set_reset);
+
+static int ezusb_ihex_firmware_download(struct usb_device *dev,
+					struct ezusb_fx_type fx,
+					const char *firmware_path)
+{
+	int ret = -ENOENT;
+	const struct firmware *firmware = NULL;
+	const struct ihex_binrec *record;
+
+	if (request_ihex_firmware(&firmware, firmware_path,
+				  &dev->dev)) {
+		dev_err(&dev->dev,
+			"%s - request \"%s\" failed\n",
+			__func__, firmware_path);
+		goto out;
+	}
+
+	ret = ezusb_set_reset(dev, fx.cpucs_reg, 0);
+	if (ret < 0)
+		goto out;
+
+	record = (const struct ihex_binrec *)firmware->data;
+	for (; record; record = ihex_next_binrec(record)) {
+		if (be32_to_cpu(record->addr) > fx.max_internal_adress) {
+			ret = ezusb_writememory(dev, be32_to_cpu(record->addr),
+						(unsigned char *)record->data,
+						be16_to_cpu(record->len), WRITE_EXT_RAM);
+			if (ret < 0) {
+				dev_err(&dev->dev, "%s - ezusb_writememory "
+					"failed writing internal memory "
+					"(%d %04X %p %d)\n", __func__, ret,
+					be32_to_cpu(record->addr), record->data,
+					be16_to_cpu(record->len));
+				goto out;
+			}
+		}
+	}
+
+	ret = ezusb_set_reset(dev, fx.cpucs_reg, 1);
+	if (ret < 0)
+		goto out;
+	record = (const struct ihex_binrec *)firmware->data;
+	for (; record; record = ihex_next_binrec(record)) {
+		if (be32_to_cpu(record->addr) <= fx.max_internal_adress) {
+			ret = ezusb_writememory(dev, be32_to_cpu(record->addr),
+						(unsigned char *)record->data,
+						be16_to_cpu(record->len), WRITE_INT_RAM);
+			if (ret < 0) {
+				dev_err(&dev->dev, "%s - ezusb_writememory "
+					"failed writing external memory "
+					"(%d %04X %p %d)\n", __func__, ret,
+					be32_to_cpu(record->addr), record->data,
+					be16_to_cpu(record->len));
+				goto out;
+			}
+		}
+	}
+	ret = ezusb_set_reset(dev, fx.cpucs_reg, 0);
+out:
+	release_firmware(firmware);
+	return ret;
+}
+
+int ezusb_fx1_ihex_firmware_download(struct usb_device *dev,
+				     const char *firmware_path)
+{
+	return ezusb_ihex_firmware_download(dev, ezusb_fx1, firmware_path);
+}
+EXPORT_SYMBOL_GPL(ezusb_fx1_ihex_firmware_download);
+
+#if 0
+/*
+ * Once someone one needs these fx2 functions, uncomment them
+ * and add them to ezusb.h and all should be good.
+ */
+static struct ezusb_fx_type ezusb_fx2 = {
+	.cpucs_reg = 0xE600,
+	.max_internal_adress = 0x3FFF,
+};
+
+int ezusb_fx2_set_reset(struct usb_device *dev, unsigned char reset_bit)
+{
+	return ezusb_set_reset(dev, ezusb_fx2.cpucs_reg, reset_bit);
+}
+EXPORT_SYMBOL_GPL(ezusb_fx2_set_reset);
+
+int ezusb_fx2_ihex_firmware_download(struct usb_device *dev,
+				     const char *firmware_path)
+{
+	return ezusb_ihex_firmware_download(dev, ezusb_fx2, firmware_path);
+}
+EXPORT_SYMBOL_GPL(ezusb_fx2_ihex_firmware_download);
+#endif
+
+MODULE_DESCRIPTION("EZUSB device support");
+MODULE_LICENSE("GPL");