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, 91 insertions, 0 deletions

diff --git a/drivers/usb/gadget/usbstring.c b/drivers/usb/gadget/usbstring.c
new file mode 100644
index 000000000..37a2f1b61
--- /dev/null
+++ b/drivers/usb/gadget/usbstring.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: LGPL-2.1+
+/*
+ * Copyright (C) 2003 David Brownell
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/string.h>
+#include <linux/device.h>
+#include <linux/nls.h>
+
+#include <linux/usb/ch9.h>
+#include <linux/usb/gadget.h>
+
+
+/**
+ * usb_gadget_get_string - fill out a string descriptor 
+ * @table: of c strings encoded using UTF-8
+ * @id: string id, from low byte of wValue in get string descriptor
+ * @buf: at least 256 bytes, must be 16-bit aligned
+ *
+ * Finds the UTF-8 string matching the ID, and converts it into a
+ * string descriptor in utf16-le.
+ * Returns length of descriptor (always even) or negative errno
+ *
+ * If your driver needs stings in multiple languages, you'll probably
+ * "switch (wIndex) { ... }"  in your ep0 string descriptor logic,
+ * using this routine after choosing which set of UTF-8 strings to use.
+ * Note that US-ASCII is a strict subset of UTF-8; any string bytes with
+ * the eighth bit set will be multibyte UTF-8 characters, not ISO-8859/1
+ * characters (which are also widely used in C strings).
+ */
+int
+usb_gadget_get_string (const struct usb_gadget_strings *table, int id, u8 *buf)
+{
+	struct usb_string	*s;
+	int			len;
+
+	/* descriptor 0 has the language id */
+	if (id == 0) {
+		buf [0] = 4;
+		buf [1] = USB_DT_STRING;
+		buf [2] = (u8) table->language;
+		buf [3] = (u8) (table->language >> 8);
+		return 4;
+	}
+	for (s = table->strings; s && s->s; s++)
+		if (s->id == id)
+			break;
+
+	/* unrecognized: stall. */
+	if (!s || !s->s)
+		return -EINVAL;
+
+	/* string descriptors have length, tag, then UTF16-LE text */
+	len = min_t(size_t, USB_MAX_STRING_LEN, strlen(s->s));
+	len = utf8s_to_utf16s(s->s, len, UTF16_LITTLE_ENDIAN,
+			(wchar_t *) &buf[2], USB_MAX_STRING_LEN);
+	if (len < 0)
+		return -EINVAL;
+	buf [0] = (len + 1) * 2;
+	buf [1] = USB_DT_STRING;
+	return buf [0];
+}
+EXPORT_SYMBOL_GPL(usb_gadget_get_string);
+
+/**
+ * usb_validate_langid - validate usb language identifiers
+ * @langid: usb language identifier
+ *
+ * Returns true for valid language identifier, otherwise false.
+ */
+bool usb_validate_langid(u16 langid)
+{
+	u16 primary_lang = langid & 0x3ff;	/* bit [9:0] */
+	u16 sub_lang = langid >> 10;		/* bit [15:10] */
+
+	switch (primary_lang) {
+	case 0:
+	case 0x62 ... 0xfe:
+	case 0x100 ... 0x3ff:
+		return false;
+	}
+	if (!sub_lang)
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(usb_validate_langid);