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, 76 insertions, 0 deletions

diff --git a/scripts/checkversion.pl b/scripts/checkversion.pl
new file mode 100755
index 000000000..94cd49eff
--- /dev/null
+++ b/scripts/checkversion.pl
@@ -0,0 +1,76 @@
+#! /usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# checkversion finds uses of all macros in <linux/version.h>
+# where the source files do not #include <linux/version.h>; or cases
+# of including <linux/version.h> where it is not needed.
+# Copyright (C) 2003, Randy Dunlap <rdunlap@infradead.org>
+
+use strict;
+
+$| = 1;
+
+my $debugging;
+
+foreach my $file (@ARGV) {
+    next if $file =~ "include/generated/uapi/linux/version\.h";
+    next if $file =~ "usr/include/linux/version\.h";
+    # Open this file.
+    open( my $f, '<', $file )
+      or die "Can't open $file: $!\n";
+
+    # Initialize variables.
+    my ($fInComment, $fInString, $fUseVersion);
+    my $iLinuxVersion = 0;
+
+    while (<$f>) {
+	# Strip comments.
+	$fInComment && (s+^.*?\*/+ +o ? ($fInComment = 0) : next);
+	m+/\*+o && (s+/\*.*?\*/+ +go, (s+/\*.*$+ +o && ($fInComment = 1)));
+
+	# Pick up definitions.
+	if ( m/^\s*#/o ) {
+	    $iLinuxVersion      = $. if m/^\s*#\s*include\s*"linux\/version\.h"/o;
+	}
+
+	# Strip strings.
+	$fInString && (s+^.*?"+ +o ? ($fInString = 0) : next);
+	m+"+o && (s+".*?"+ +go, (s+".*$+ +o && ($fInString = 1)));
+
+	# Pick up definitions.
+	if ( m/^\s*#/o ) {
+	    $iLinuxVersion      = $. if m/^\s*#\s*include\s*<linux\/version\.h>/o;
+	}
+
+	# Look for uses: LINUX_VERSION_CODE, KERNEL_VERSION,
+	# LINUX_VERSION_MAJOR, LINUX_VERSION_PATCHLEVEL, LINUX_VERSION_SUBLEVEL
+	if (($_ =~ /LINUX_VERSION_CODE/) || ($_ =~ /\WKERNEL_VERSION/) ||
+	    ($_ =~ /LINUX_VERSION_MAJOR/) || ($_ =~ /LINUX_VERSION_PATCHLEVEL/) ||
+	    ($_ =~ /LINUX_VERSION_SUBLEVEL/)) {
+	    $fUseVersion = 1;
+            last if $iLinuxVersion;
+        }
+    }
+
+    # Report used version IDs without include?
+    if ($fUseVersion && ! $iLinuxVersion) {
+	print "$file: $.: need linux/version.h\n";
+    }
+
+    # Report superfluous includes.
+    if ($iLinuxVersion && ! $fUseVersion) {
+	print "$file: $iLinuxVersion linux/version.h not needed.\n";
+    }
+
+    # debug: report OK results:
+    if ($debugging) {
+        if ($iLinuxVersion && $fUseVersion) {
+	    print "$file: version use is OK ($iLinuxVersion)\n";
+        }
+        if (! $iLinuxVersion && ! $fUseVersion) {
+	    print "$file: version use is OK (none)\n";
+        }
+    }
+
+    close($f);
+}