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, 232 insertions, 0 deletions

diff --git a/include/kunit/assert.h b/include/kunit/assert.h
new file mode 100644
index 000000000..bb879389f
--- /dev/null
+++ b/include/kunit/assert.h
@@ -0,0 +1,232 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Assertion and expectation serialization API.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_ASSERT_H
+#define _KUNIT_ASSERT_H
+
+#include <linux/err.h>
+#include <linux/printk.h>
+
+struct kunit;
+struct string_stream;
+
+/**
+ * enum kunit_assert_type - Type of expectation/assertion.
+ * @KUNIT_ASSERTION: Used to denote that a kunit_assert represents an assertion.
+ * @KUNIT_EXPECTATION: Denotes that a kunit_assert represents an expectation.
+ *
+ * Used in conjunction with a &struct kunit_assert to denote whether it
+ * represents an expectation or an assertion.
+ */
+enum kunit_assert_type {
+	KUNIT_ASSERTION,
+	KUNIT_EXPECTATION,
+};
+
+/**
+ * struct kunit_loc - Identifies the source location of a line of code.
+ * @line: the line number in the file.
+ * @file: the file name.
+ */
+struct kunit_loc {
+	int line;
+	const char *file;
+};
+
+#define KUNIT_CURRENT_LOC { .file = __FILE__, .line = __LINE__ }
+
+/**
+ * struct kunit_assert - Data for printing a failed assertion or expectation.
+ *
+ * Represents a failed expectation/assertion. Contains all the data necessary to
+ * format a string to a user reporting the failure.
+ */
+struct kunit_assert {};
+
+typedef void (*assert_format_t)(const struct kunit_assert *assert,
+				const struct va_format *message,
+				struct string_stream *stream);
+
+void kunit_assert_prologue(const struct kunit_loc *loc,
+			   enum kunit_assert_type type,
+			   struct string_stream *stream);
+
+/**
+ * struct kunit_fail_assert - Represents a plain fail expectation/assertion.
+ * @assert: The parent of this type.
+ *
+ * Represents a simple KUNIT_FAIL/KUNIT_FAIL_AND_ABORT that always fails.
+ */
+struct kunit_fail_assert {
+	struct kunit_assert assert;
+};
+
+void kunit_fail_assert_format(const struct kunit_assert *assert,
+			      const struct va_format *message,
+			      struct string_stream *stream);
+
+/**
+ * struct kunit_unary_assert - Represents a KUNIT_{EXPECT|ASSERT}_{TRUE|FALSE}
+ * @assert: The parent of this type.
+ * @condition: A string representation of a conditional expression.
+ * @expected_true: True if of type KUNIT_{EXPECT|ASSERT}_TRUE, false otherwise.
+ *
+ * Represents a simple expectation or assertion that simply asserts something is
+ * true or false. In other words, represents the expectations:
+ * KUNIT_{EXPECT|ASSERT}_{TRUE|FALSE}
+ */
+struct kunit_unary_assert {
+	struct kunit_assert assert;
+	const char *condition;
+	bool expected_true;
+};
+
+void kunit_unary_assert_format(const struct kunit_assert *assert,
+			       const struct va_format *message,
+			       struct string_stream *stream);
+
+/**
+ * struct kunit_ptr_not_err_assert - An expectation/assertion that a pointer is
+ *	not NULL and not a -errno.
+ * @assert: The parent of this type.
+ * @text: A string representation of the expression passed to the expectation.
+ * @value: The actual evaluated pointer value of the expression.
+ *
+ * Represents an expectation/assertion that a pointer is not null and is does
+ * not contain a -errno. (See IS_ERR_OR_NULL().)
+ */
+struct kunit_ptr_not_err_assert {
+	struct kunit_assert assert;
+	const char *text;
+	const void *value;
+};
+
+void kunit_ptr_not_err_assert_format(const struct kunit_assert *assert,
+				     const struct va_format *message,
+				     struct string_stream *stream);
+
+/**
+ * struct kunit_binary_assert_text - holds strings for &struct
+ *	kunit_binary_assert and friends to try and make the structs smaller.
+ * @operation: A string representation of the comparison operator (e.g. "==").
+ * @left_text: A string representation of the left expression (e.g. "2+2").
+ * @right_text: A string representation of the right expression (e.g. "2+2").
+ */
+struct kunit_binary_assert_text {
+	const char *operation;
+	const char *left_text;
+	const char *right_text;
+};
+
+/**
+ * struct kunit_binary_assert - An expectation/assertion that compares two
+ *	non-pointer values (for example, KUNIT_EXPECT_EQ(test, 1 + 1, 2)).
+ * @assert: The parent of this type.
+ * @text: Holds the textual representations of the operands and op (e.g.  "==").
+ * @left_value: The actual evaluated value of the expression in the left slot.
+ * @right_value: The actual evaluated value of the expression in the right slot.
+ *
+ * Represents an expectation/assertion that compares two non-pointer values. For
+ * example, to expect that 1 + 1 == 2, you can use the expectation
+ * KUNIT_EXPECT_EQ(test, 1 + 1, 2);
+ */
+struct kunit_binary_assert {
+	struct kunit_assert assert;
+	const struct kunit_binary_assert_text *text;
+	long long left_value;
+	long long right_value;
+};
+
+void kunit_binary_assert_format(const struct kunit_assert *assert,
+				const struct va_format *message,
+				struct string_stream *stream);
+
+/**
+ * struct kunit_binary_ptr_assert - An expectation/assertion that compares two
+ *	pointer values (for example, KUNIT_EXPECT_PTR_EQ(test, foo, bar)).
+ * @assert: The parent of this type.
+ * @text: Holds the textual representations of the operands and op (e.g.  "==").
+ * @left_value: The actual evaluated value of the expression in the left slot.
+ * @right_value: The actual evaluated value of the expression in the right slot.
+ *
+ * Represents an expectation/assertion that compares two pointer values. For
+ * example, to expect that foo and bar point to the same thing, you can use the
+ * expectation KUNIT_EXPECT_PTR_EQ(test, foo, bar);
+ */
+struct kunit_binary_ptr_assert {
+	struct kunit_assert assert;
+	const struct kunit_binary_assert_text *text;
+	const void *left_value;
+	const void *right_value;
+};
+
+void kunit_binary_ptr_assert_format(const struct kunit_assert *assert,
+				    const struct va_format *message,
+				    struct string_stream *stream);
+
+/**
+ * struct kunit_binary_str_assert - An expectation/assertion that compares two
+ *	string values (for example, KUNIT_EXPECT_STREQ(test, foo, "bar")).
+ * @assert: The parent of this type.
+ * @text: Holds the textual representations of the operands and comparator.
+ * @left_value: The actual evaluated value of the expression in the left slot.
+ * @right_value: The actual evaluated value of the expression in the right slot.
+ *
+ * Represents an expectation/assertion that compares two string values. For
+ * example, to expect that the string in foo is equal to "bar", you can use the
+ * expectation KUNIT_EXPECT_STREQ(test, foo, "bar");
+ */
+struct kunit_binary_str_assert {
+	struct kunit_assert assert;
+	const struct kunit_binary_assert_text *text;
+	const char *left_value;
+	const char *right_value;
+};
+
+void kunit_binary_str_assert_format(const struct kunit_assert *assert,
+				    const struct va_format *message,
+				    struct string_stream *stream);
+
+/**
+ * struct kunit_mem_assert - An expectation/assertion that compares two
+ *	memory blocks.
+ * @assert: The parent of this type.
+ * @text: Holds the textual representations of the operands and comparator.
+ * @left_value: The actual evaluated value of the expression in the left slot.
+ * @right_value: The actual evaluated value of the expression in the right slot.
+ * @size: Size of the memory block analysed in bytes.
+ *
+ * Represents an expectation/assertion that compares two memory blocks. For
+ * example, to expect that the first three bytes of foo is equal to the
+ * first three bytes of bar, you can use the expectation
+ * KUNIT_EXPECT_MEMEQ(test, foo, bar, 3);
+ */
+struct kunit_mem_assert {
+	struct kunit_assert assert;
+	const struct kunit_binary_assert_text *text;
+	const void *left_value;
+	const void *right_value;
+	const size_t size;
+};
+
+void kunit_mem_assert_format(const struct kunit_assert *assert,
+			     const struct va_format *message,
+			     struct string_stream *stream);
+
+#if IS_ENABLED(CONFIG_KUNIT)
+void kunit_assert_print_msg(const struct va_format *message,
+			    struct string_stream *stream);
+bool is_literal(const char *text, long long value);
+bool is_str_literal(const char *text, const char *value);
+void kunit_assert_hexdump(struct string_stream *stream,
+			  const void *buf,
+			  const void *compared_buf,
+			  const size_t len);
+#endif
+
+#endif /*  _KUNIT_ASSERT_H */