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

13 files changed, 191 insertions, 0 deletions

diff --git a/scripts/kconfig/tests/preprocess/builtin_func/Kconfig b/scripts/kconfig/tests/preprocess/builtin_func/Kconfig
new file mode 100644
index 000000000..baa328827
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/builtin_func/Kconfig
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# 'info' prints the argument to stdout.
+$(info,hello world 0)
+
+# 'warning-if', if the first argument is y, sends the second argument to stderr,
+# and the message is prefixed with the current file name and line number.
+$(warning-if,y,hello world 1)
+
+# 'error-if' is similar, but it terminates the parsing immediately.
+# The following is just no-op since the first argument is not y.
+$(error-if,n,this should not be printed)
+
+# Shorthand
+warning = $(warning-if,y,$(1))
+
+# 'shell' executes a command, and returns its stdout.
+$(warning,$(shell,echo hello world 3))
+
+# Every newline in the output is replaced with a space,
+# but any trailing newlines are deleted.
+$(warning,$(shell,printf 'hello\nworld\n\n4\n\n\n'))
+
+# 'filename' is expanded to the currently parsed file name,
+# 'lineno' to the line number.
+$(warning,filename=$(filename))
+$(warning,lineno=$(lineno))
diff --git a/scripts/kconfig/tests/preprocess/builtin_func/__init__.py b/scripts/kconfig/tests/preprocess/builtin_func/__init__.py
new file mode 100644
index 000000000..2e53ba08f
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/builtin_func/__init__.py
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Built-in function tests.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() == 0
+    assert conf.stdout_contains('expected_stdout')
+    assert conf.stderr_matches('expected_stderr')
diff --git a/scripts/kconfig/tests/preprocess/builtin_func/expected_stderr b/scripts/kconfig/tests/preprocess/builtin_func/expected_stderr
new file mode 100644
index 000000000..33ea9ca38
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/builtin_func/expected_stderr
@@ -0,0 +1,5 @@
+Kconfig:8: hello world 1
+Kconfig:18: hello world 3
+Kconfig:22: hello world  4
+Kconfig:26: filename=Kconfig
+Kconfig:27: lineno=27
diff --git a/scripts/kconfig/tests/preprocess/builtin_func/expected_stdout b/scripts/kconfig/tests/preprocess/builtin_func/expected_stdout
new file mode 100644
index 000000000..82de3a7e9
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/builtin_func/expected_stdout
@@ -0,0 +1 @@
+hello world 0
diff --git a/scripts/kconfig/tests/preprocess/circular_expansion/Kconfig b/scripts/kconfig/tests/preprocess/circular_expansion/Kconfig
new file mode 100644
index 000000000..6838997c2
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/circular_expansion/Kconfig
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+X = $(Y)
+Y = $(X)
+$(info $(X))
diff --git a/scripts/kconfig/tests/preprocess/circular_expansion/__init__.py b/scripts/kconfig/tests/preprocess/circular_expansion/__init__.py
new file mode 100644
index 000000000..419bda3e0
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/circular_expansion/__init__.py
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Detect circular variable expansion.
+
+If a recursively expanded variable references itself (eventually),
+it should fail with an error message.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() != 0
+    assert conf.stderr_matches('expected_stderr')
diff --git a/scripts/kconfig/tests/preprocess/circular_expansion/expected_stderr b/scripts/kconfig/tests/preprocess/circular_expansion/expected_stderr
new file mode 100644
index 000000000..cde68fa98
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/circular_expansion/expected_stderr
@@ -0,0 +1 @@
+Kconfig:5: Recursive variable 'X' references itself (eventually)
diff --git a/scripts/kconfig/tests/preprocess/escape/Kconfig b/scripts/kconfig/tests/preprocess/escape/Kconfig
new file mode 100644
index 000000000..4e3f44445
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/escape/Kconfig
@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Shorthand
+warning = $(warning-if,y,$(1))
+
+# You can not pass commas directly to a function since they are treated as
+# delimiters. You can use the following trick to do so.
+comma   := ,
+$(warning,hello$(comma) world)
+
+# Like Make, single quotes, double quotes, spaces are treated verbatim.
+# The following prints the text as-is.
+$(warning,  ' " '"   ' ''' "'")
+
+# Unlike Make, '$' has special meaning only when it is followed by '('.
+# No need to escape '$' itself.
+$(warning,$)
+$(warning,$$)
+$ := 1
+$(warning,$($))
+
+# You need a trick to escape '$' followed by '('
+# The following should print "$(X)". It should not be expanded further.
+dollar := $
+$(warning,$(dollar)(X))
+
+# You need a trick to treat unbalanced parentheses.
+# The following should print "(".
+left_paren := (
+$(warning,$(left_paren))
+
+# A simple expanded should not be expanded multiple times.
+# The following should print "$(X)". It should not be expanded further.
+Y := $(dollar)(X)
+$(warning,$(Y))
+
+# The following should print "$(X)" as well.
+Y = $(dollar)(X)
+$(warning,$(Y))
+
+# The following should print "$(".
+# It should not be emit "unterminated reference" error.
+unterminated := $(dollar)(
+$(warning,$(unterminated))
diff --git a/scripts/kconfig/tests/preprocess/escape/__init__.py b/scripts/kconfig/tests/preprocess/escape/__init__.py
new file mode 100644
index 000000000..7ee8e747f
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/escape/__init__.py
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Escape sequence tests.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() == 0
+    assert conf.stderr_matches('expected_stderr')
diff --git a/scripts/kconfig/tests/preprocess/escape/expected_stderr b/scripts/kconfig/tests/preprocess/escape/expected_stderr
new file mode 100644
index 000000000..1c00957dd
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/escape/expected_stderr
@@ -0,0 +1,10 @@
+Kconfig:9: hello, world
+Kconfig:13:   ' " '"   ' ''' "'"
+Kconfig:17: $
+Kconfig:18: $$
+Kconfig:20: 1
+Kconfig:25: $(X)
+Kconfig:30: (
+Kconfig:35: $(X)
+Kconfig:39: $(X)
+Kconfig:44: $(
diff --git a/scripts/kconfig/tests/preprocess/variable/Kconfig b/scripts/kconfig/tests/preprocess/variable/Kconfig
new file mode 100644
index 000000000..9ce2f95cb
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/variable/Kconfig
@@ -0,0 +1,53 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Shorthand
+warning = $(warning-if,y,$(1))
+
+# Simply expanded variable.
+X := 1
+SIMPLE := $(X)
+X := 2
+$(warning,SIMPLE = $(SIMPLE))
+
+# Recursively expanded variable.
+X := 1
+RECURSIVE = $(X)
+X := 2
+$(warning,RECURSIVE = $(RECURSIVE))
+
+# Append something to a simply expanded variable.
+Y := 3
+SIMPLE += $(Y)
+Y := 4
+$(warning,SIMPLE = $(SIMPLE))
+
+# Append something to a recursively expanded variable.
+Y := 3
+RECURSIVE += $(Y)
+Y := 4
+$(warning,RECURSIVE = $(RECURSIVE))
+
+# Use += operator to an undefined variable.
+# This works as a recursively expanded variable.
+Y := 3
+UNDEFINED_VARIABLE += $(Y)
+Y := 4
+$(warning,UNDEFINED_VARIABLE = $(UNDEFINED_VARIABLE))
+
+# You can use variable references for the lefthand side of assignment statement.
+X := A
+Y := B
+$(X)$(Y) := 5
+$(warning,AB = $(AB))
+
+# User-defined function.
+greeting = $(1), my name is $(2).
+$(warning,$(greeting,Hello,John))
+
+# The number of arguments is not checked for user-defined functions.
+# If some arguments are optional, it is useful to pass fewer parameters.
+# $(2) will be blank in this case.
+$(warning,$(greeting,Hello))
+
+# Unreferenced parameters are just ignored.
+$(warning,$(greeting,Hello,John,ignored,ignored))
diff --git a/scripts/kconfig/tests/preprocess/variable/__init__.py b/scripts/kconfig/tests/preprocess/variable/__init__.py
new file mode 100644
index 000000000..e88b1708d
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/variable/__init__.py
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Variable and user-defined function tests.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() == 0
+    assert conf.stderr_matches('expected_stderr')
diff --git a/scripts/kconfig/tests/preprocess/variable/expected_stderr b/scripts/kconfig/tests/preprocess/variable/expected_stderr
new file mode 100644
index 000000000..a4841c3fd
--- /dev/null
+++ b/scripts/kconfig/tests/preprocess/variable/expected_stderr
@@ -0,0 +1,9 @@
+Kconfig:10: SIMPLE = 1
+Kconfig:16: RECURSIVE = 2
+Kconfig:22: SIMPLE = 1 3
+Kconfig:28: RECURSIVE = 2 4
+Kconfig:35: UNDEFINED_VARIABLE = 4
+Kconfig:41: AB = 5
+Kconfig:45: Hello, my name is John.
+Kconfig:50: Hello, my name is .
+Kconfig:53: Hello, my name is John.