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, 318 insertions, 0 deletions

diff --git a/scripts/kconfig/tests/conftest.py b/scripts/kconfig/tests/conftest.py
new file mode 100644
index 000000000..66f95e4ed
--- /dev/null
+++ b/scripts/kconfig/tests/conftest.py
@@ -0,0 +1,318 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2018 Masahiro Yamada <yamada.masahiro@socionext.com>
+#
+
+"""
+Kconfig unit testing framework.
+
+This provides fixture functions commonly used from test files.
+"""
+
+import os
+import pytest
+import shutil
+import subprocess
+import tempfile
+
+CONF_PATH = os.path.abspath(os.path.join('scripts', 'kconfig', 'conf'))
+
+
+class Conf:
+    """Kconfig runner and result checker.
+
+    This class provides methods to run text-based interface of Kconfig
+    (scripts/kconfig/conf) and retrieve the resulted configuration,
+    stdout, and stderr.  It also provides methods to compare those
+    results with expectations.
+    """
+
+    def __init__(self, request):
+        """Create a new Conf instance.
+
+        request: object to introspect the requesting test module
+        """
+        # the directory of the test being run
+        self._test_dir = os.path.dirname(str(request.fspath))
+
+    # runners
+    def _run_conf(self, mode, dot_config=None, out_file='.config',
+                  interactive=False, in_keys=None, extra_env={},
+                  silent=False):
+        """Run text-based Kconfig executable and save the result.
+
+        mode: input mode option (--oldaskconfig, --defconfig=<file> etc.)
+        dot_config: .config file to use for configuration base
+        out_file: file name to contain the output config data
+        interactive: flag to specify the interactive mode
+        in_keys: key inputs for interactive modes
+        extra_env: additional environments
+        returncode: exit status of the Kconfig executable
+        """
+        command = [CONF_PATH]
+        if silent:
+            command.append('-s')
+        command += [mode, 'Kconfig']
+
+        # Override 'srctree' environment to make the test as the top directory
+        extra_env['srctree'] = self._test_dir
+
+        # Clear KCONFIG_DEFCONFIG_LIST to keep unit tests from being affected
+        # by the user's environment.
+        extra_env['KCONFIG_DEFCONFIG_LIST'] = ''
+
+        # Run Kconfig in a temporary directory.
+        # This directory is automatically removed when done.
+        with tempfile.TemporaryDirectory() as temp_dir:
+
+            # if .config is given, copy it to the working directory
+            if dot_config:
+                shutil.copyfile(os.path.join(self._test_dir, dot_config),
+                                os.path.join(temp_dir, '.config'))
+
+            ps = subprocess.Popen(command,
+                                  stdin=subprocess.PIPE,
+                                  stdout=subprocess.PIPE,
+                                  stderr=subprocess.PIPE,
+                                  cwd=temp_dir,
+                                  env=dict(os.environ, **extra_env))
+
+            # If input key sequence is given, feed it to stdin.
+            if in_keys:
+                ps.stdin.write(in_keys.encode('utf-8'))
+
+            while ps.poll() is None:
+                # For interactive modes such as oldaskconfig, oldconfig,
+                # send 'Enter' key until the program finishes.
+                if interactive:
+                    try:
+                        ps.stdin.write(b'\n')
+                        ps.stdin.flush()
+                    except (BrokenPipeError, OSError):
+                        # Process has exited, stop sending input
+                        break
+
+            # Close stdin gracefully
+            try:
+                ps.stdin.close()
+            except (BrokenPipeError, OSError):
+                # Ignore broken pipe on close
+                pass
+
+            # Wait for process to complete
+            ps.wait()
+
+            self.retcode = ps.returncode
+            self.stdout = ps.stdout.read().decode()
+            self.stderr = ps.stderr.read().decode()
+
+            # Retrieve the resulted config data only when .config is supposed
+            # to exist.  If the command fails, the .config does not exist.
+            # 'listnewconfig' does not produce .config in the first place.
+            if self.retcode == 0 and out_file:
+                with open(os.path.join(temp_dir, out_file)) as f:
+                    self.config = f.read()
+            else:
+                self.config = None
+
+        # Logging:
+        # Pytest captures the following information by default.  In failure
+        # of tests, the captured log will be displayed.  This will be useful to
+        # figure out what has happened.
+
+        print("[command]\n{}\n".format(' '.join(command)))
+
+        print("[retcode]\n{}\n".format(self.retcode))
+
+        print("[stdout]")
+        print(self.stdout)
+
+        print("[stderr]")
+        print(self.stderr)
+
+        if self.config is not None:
+            print("[output for '{}']".format(out_file))
+            print(self.config)
+
+        return self.retcode
+
+    def oldaskconfig(self, dot_config=None, in_keys=None):
+        """Run oldaskconfig.
+
+        dot_config: .config file to use for configuration base (optional)
+        in_key: key inputs (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._run_conf('--oldaskconfig', dot_config=dot_config,
+                              interactive=True, in_keys=in_keys)
+
+    def oldconfig(self, dot_config=None, in_keys=None):
+        """Run oldconfig.
+
+        dot_config: .config file to use for configuration base (optional)
+        in_key: key inputs (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._run_conf('--oldconfig', dot_config=dot_config,
+                              interactive=True, in_keys=in_keys)
+
+    def olddefconfig(self, dot_config=None):
+        """Run olddefconfig.
+
+        dot_config: .config file to use for configuration base (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._run_conf('--olddefconfig', dot_config=dot_config)
+
+    def defconfig(self, defconfig):
+        """Run defconfig.
+
+        defconfig: defconfig file for input
+        returncode: exit status of the Kconfig executable
+        """
+        defconfig_path = os.path.join(self._test_dir, defconfig)
+        return self._run_conf('--defconfig={}'.format(defconfig_path))
+
+    def _allconfig(self, mode, all_config, extra_env={}):
+        if all_config:
+            all_config_path = os.path.join(self._test_dir, all_config)
+            extra_env['KCONFIG_ALLCONFIG'] = all_config_path
+
+        return self._run_conf('--{}config'.format(mode), extra_env=extra_env)
+
+    def allyesconfig(self, all_config=None):
+        """Run allyesconfig.
+
+        all_config: fragment config file for KCONFIG_ALLCONFIG (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._allconfig('allyes', all_config)
+
+    def allmodconfig(self, all_config=None):
+        """Run allmodconfig.
+
+        all_config: fragment config file for KCONFIG_ALLCONFIG (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._allconfig('allmod', all_config)
+
+    def allnoconfig(self, all_config=None):
+        """Run allnoconfig.
+
+        all_config: fragment config file for KCONFIG_ALLCONFIG (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._allconfig('allno', all_config)
+
+    def alldefconfig(self, all_config=None):
+        """Run alldefconfig.
+
+        all_config: fragment config file for KCONFIG_ALLCONFIG (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._allconfig('alldef', all_config)
+
+    def randconfig(self, all_config=None, seed=None):
+        """Run randconfig.
+
+        all_config: fragment config file for KCONFIG_ALLCONFIG (optional)
+        seed: the seed for randconfig (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        if seed is not None:
+            extra_env = {'KCONFIG_SEED': hex(seed)}
+        else:
+            extra_env = {}
+
+        return self._allconfig('rand', all_config, extra_env=extra_env)
+
+    def savedefconfig(self, dot_config):
+        """Run savedefconfig.
+
+        dot_config: .config file for input
+        returncode: exit status of the Kconfig executable
+        """
+        return self._run_conf('--savedefconfig', out_file='defconfig')
+
+    def listnewconfig(self, dot_config=None):
+        """Run listnewconfig.
+
+        dot_config: .config file to use for configuration base (optional)
+        returncode: exit status of the Kconfig executable
+        """
+        return self._run_conf('--listnewconfig', dot_config=dot_config,
+                              out_file=None)
+
+    # checkers
+    def _read_and_compare(self, compare, expected):
+        """Compare the result with expectation.
+
+        compare: function to compare the result with expectation
+        expected: file that contains the expected data
+        """
+        with open(os.path.join(self._test_dir, expected)) as f:
+            expected_data = f.read()
+        return compare(self, expected_data)
+
+    def _contains(self, attr, expected):
+        return self._read_and_compare(
+                                    lambda s, e: getattr(s, attr).find(e) >= 0,
+                                    expected)
+
+    def _matches(self, attr, expected):
+        return self._read_and_compare(lambda s, e: getattr(s, attr) == e,
+                                      expected)
+
+    def config_contains(self, expected):
+        """Check if resulted configuration contains expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result contains the expected data, False otherwise
+        """
+        return self._contains('config', expected)
+
+    def config_matches(self, expected):
+        """Check if resulted configuration exactly matches expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result matches the expected data, False otherwise
+        """
+        return self._matches('config', expected)
+
+    def stdout_contains(self, expected):
+        """Check if resulted stdout contains expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result contains the expected data, False otherwise
+        """
+        return self._contains('stdout', expected)
+
+    def stdout_matches(self, expected):
+        """Check if resulted stdout exactly matches expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result matches the expected data, False otherwise
+        """
+        return self._matches('stdout', expected)
+
+    def stderr_contains(self, expected):
+        """Check if resulted stderr contains expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result contains the expected data, False otherwise
+        """
+        return self._contains('stderr', expected)
+
+    def stderr_matches(self, expected):
+        """Check if resulted stderr exactly matches expected data.
+
+        expected: file that contains the expected data
+        returncode: True if result matches the expected data, False otherwise
+        """
+        return self._matches('stderr', expected)
+
+
+@pytest.fixture(scope="module")
+def conf(request):
+    """Create a Conf instance and provide it to test functions."""
+    return Conf(request)