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, 214 insertions, 0 deletions

diff --git a/tools/docs/get_abi.py b/tools/docs/get_abi.py
new file mode 100755
index 000000000..2f0b99401
--- /dev/null
+++ b/tools/docs/get_abi.py
@@ -0,0 +1,214 @@
+#!/usr/bin/env python3
+# pylint: disable=R0903
+# Copyright(c) 2025: Mauro Carvalho Chehab <mchehab@kernel.org>.
+# SPDX-License-Identifier: GPL-2.0
+
+"""
+Parse ABI documentation and produce results from it.
+"""
+
+import argparse
+import logging
+import os
+import sys
+
+# Import Python modules
+
+LIB_DIR = "../lib/python"
+SRC_DIR = os.path.dirname(os.path.realpath(__file__))
+
+sys.path.insert(0, os.path.join(SRC_DIR, LIB_DIR))
+
+from abi.abi_parser import AbiParser                # pylint: disable=C0413
+from abi.abi_regex import AbiRegex                  # pylint: disable=C0413
+from abi.helpers import ABI_DIR, DEBUG_HELP         # pylint: disable=C0413
+from abi.system_symbols import SystemSymbols        # pylint: disable=C0413
+
+# Command line classes
+
+
+REST_DESC = """
+Produce output in ReST format.
+
+The output is done on two sections:
+
+- Symbols: show all parsed symbols in alphabetic order;
+- Files: cross reference the content of each file with the symbols on it.
+"""
+
+class AbiRest:
+    """Initialize an argparse subparser for rest output"""
+
+    def __init__(self, subparsers):
+        """Initialize argparse subparsers"""
+
+        parser = subparsers.add_parser("rest",
+                                       formatter_class=argparse.RawTextHelpFormatter,
+                                       description=REST_DESC)
+
+        parser.add_argument("--enable-lineno",  action="store_true",
+                            help="enable lineno")
+        parser.add_argument("--raw", action="store_true",
+                            help="output text as contained in the ABI files. "
+                                 "It not used, output will contain dynamically"
+                                 " generated cross references when possible.")
+        parser.add_argument("--no-file", action="store_true",
+                            help="Don't the files section")
+        parser.add_argument("--show-hints", help="Show-hints")
+
+        parser.set_defaults(func=self.run)
+
+    def run(self, args):
+        """Run subparser"""
+
+        parser = AbiParser(args.dir, debug=args.debug)
+        parser.parse_abi()
+        parser.check_issues()
+
+        for t in parser.doc(args.raw, not args.no_file):
+            if args.enable_lineno:
+                print (f".. LINENO {t[1]}#{t[2]}\n\n")
+
+            print(t[0])
+
+class AbiValidate:
+    """Initialize an argparse subparser for ABI validation"""
+
+    def __init__(self, subparsers):
+        """Initialize argparse subparsers"""
+
+        parser = subparsers.add_parser("validate",
+                                       formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+                                       description="list events")
+
+        parser.set_defaults(func=self.run)
+
+    def run(self, args):
+        """Run subparser"""
+
+        parser = AbiParser(args.dir, debug=args.debug)
+        parser.parse_abi()
+        parser.check_issues()
+
+
+class AbiSearch:
+    """Initialize an argparse subparser for ABI search"""
+
+    def __init__(self, subparsers):
+        """Initialize argparse subparsers"""
+
+        parser = subparsers.add_parser("search",
+                                       formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+                                       description="Search ABI using a regular expression")
+
+        parser.add_argument("expression",
+                            help="Case-insensitive search pattern for the ABI symbol")
+
+        parser.set_defaults(func=self.run)
+
+    def run(self, args):
+        """Run subparser"""
+
+        parser = AbiParser(args.dir, debug=args.debug)
+        parser.parse_abi()
+        parser.search_symbols(args.expression)
+
+UNDEFINED_DESC="""
+Check undefined ABIs on local machine.
+
+Read sysfs devnodes and check if the devnodes there are defined inside
+ABI documentation.
+
+The search logic tries to minimize the number of regular expressions to
+search per each symbol.
+
+By default, it runs on a single CPU, as Python support for CPU threads
+is still experimental, and multi-process runs on Python is very slow.
+
+On experimental tests, if the number of ABI symbols to search per devnode
+is contained on a limit of ~150 regular expressions, using a single CPU
+is a lot faster than using multiple processes. However, if the number of
+regular expressions to check is at the order of ~30000, using multiple
+CPUs speeds up the check.
+"""
+
+class AbiUndefined:
+    """
+    Initialize an argparse subparser for logic to check undefined ABI at
+    the current machine's sysfs
+    """
+
+    def __init__(self, subparsers):
+        """Initialize argparse subparsers"""
+
+        parser = subparsers.add_parser("undefined",
+                                       formatter_class=argparse.RawTextHelpFormatter,
+                                       description=UNDEFINED_DESC)
+
+        parser.add_argument("-S", "--sysfs-dir", default="/sys",
+                            help="directory where sysfs is mounted")
+        parser.add_argument("-s", "--search-string",
+                            help="search string regular expression to limit symbol search")
+        parser.add_argument("-H", "--show-hints", action="store_true",
+                            help="Hints about definitions for missing ABI symbols.")
+        parser.add_argument("-j", "--jobs", "--max-workers", type=int, default=1,
+                            help="If bigger than one, enables multiprocessing.")
+        parser.add_argument("-c", "--max-chunk-size", type=int, default=50,
+                            help="Maximum number of chunk size")
+        parser.add_argument("-f", "--found", action="store_true",
+                            help="Also show found items. "
+                                 "Helpful to debug the parser."),
+        parser.add_argument("-d", "--dry-run", action="store_true",
+                            help="Don't actually search for undefined. "
+                                 "Helpful to debug the parser."),
+
+        parser.set_defaults(func=self.run)
+
+    def run(self, args):
+        """Run subparser"""
+
+        abi = AbiRegex(args.dir, debug=args.debug,
+                       search_string=args.search_string)
+
+        abi_symbols = SystemSymbols(abi=abi, hints=args.show_hints,
+                                    sysfs=args.sysfs_dir)
+
+        abi_symbols.check_undefined_symbols(dry_run=args.dry_run,
+                                            found=args.found,
+                                            max_workers=args.jobs,
+                                            chunk_size=args.max_chunk_size)
+
+
+def main():
+    """Main program"""
+
+    parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter)
+
+    parser.add_argument("-d", "--debug", type=int, default=0, help="debug level")
+    parser.add_argument("-D", "--dir", default=ABI_DIR, help=DEBUG_HELP)
+
+    subparsers = parser.add_subparsers()
+
+    AbiRest(subparsers)
+    AbiValidate(subparsers)
+    AbiSearch(subparsers)
+    AbiUndefined(subparsers)
+
+    args = parser.parse_args()
+
+    if args.debug:
+        level = logging.DEBUG
+    else:
+        level = logging.INFO
+
+    logging.basicConfig(level=level, format="[%(levelname)s] %(message)s")
+
+    if "func" in args:
+        args.func(args)
+    else:
+        sys.exit(f"Please specify a valid command for {sys.argv[0]}")
+
+
+# Call main method
+if __name__ == "__main__":
+    main()