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, 75 insertions, 0 deletions

diff --git a/scripts/headers_install.sh b/scripts/headers_install.sh
new file mode 100755
index 000000000..2f1d1767c
--- /dev/null
+++ b/scripts/headers_install.sh
@@ -0,0 +1,75 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+if [ $# -ne 2 ]
+then
+	echo "Usage: headers_install.sh INFILE OUTFILE"
+	echo
+	echo "Prepares kernel header files for use by user space, by removing"
+	echo "all compiler.h definitions and #includes, removing any"
+	echo "#ifdef __KERNEL__ sections, and putting __underscores__ around"
+	echo "asm/inline/volatile keywords."
+	echo
+	echo "INFILE: header file to operate on"
+	echo "OUTFILE: output file which the processed header is written to"
+
+	exit 1
+fi
+
+# Grab arguments
+INFILE=$1
+OUTFILE=$2
+TMPFILE=$OUTFILE.tmp
+
+trap 'rm -f $OUTFILE $TMPFILE' EXIT
+
+# SPDX-License-Identifier with GPL variants must have "WITH Linux-syscall-note"
+if [ -n "$(sed -n -e "/SPDX-License-Identifier:.*GPL-/{/WITH Linux-syscall-note/!p}" $INFILE)" ]; then
+	echo "error: $INFILE: missing \"WITH Linux-syscall-note\" for SPDX-License-Identifier" >&2
+	exit 1
+fi
+
+sed -E -e '
+	s/([[:space:](])(__user|__force|__iomem)[[:space:]]/\1/g
+	s/__attribute_const__([[:space:]]|$)/\1/g
+	s@^#include <linux/compiler.h>@@
+	s/(^|[^a-zA-Z0-9])__packed([^a-zA-Z0-9_]|$)/\1__attribute__((packed))\2/g
+	s/(^|[[:space:](])(inline|asm|volatile)([[:space:](]|$)/\1__\2__\3/g
+	s@#(ifndef|define|endif[[:space:]]*/[*])[[:space:]]*_UAPI@#\1 @
+	s/__ASSEMBLY__/__ASSEMBLER__/g
+' $INFILE > $TMPFILE || exit 1
+
+scripts/unifdef -U__KERNEL__ -D__EXPORTED_HEADERS__ $TMPFILE > $OUTFILE
+[ $? -gt 1 ] && exit 1
+
+# Remove /* ... */ style comments, and find CONFIG_ references in code
+configs=$(sed -e '
+:comment
+	s:/\*[^*][^*]*:/*:
+	s:/\*\*\**\([^/]\):/*\1:
+	t comment
+	s:/\*\*/: :
+	t comment
+	/\/\*/! b check
+	N
+	b comment
+:print
+	P
+	D
+:check
+	s:^\(CONFIG_[[:alnum:]_]*\):\1\n:
+	t print
+	s:^[[:alnum:]_][[:alnum:]_]*::
+	s:^[^[:alnum:]_][^[:alnum:]_]*::
+	t check
+	d
+' $OUTFILE)
+
+for c in $configs
+do
+	echo "error: $INFILE: leak $c to user-space" >&2
+	exit 1
+done
+
+rm -f $TMPFILE
+trap - EXIT