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, 97 insertions, 0 deletions

diff --git a/scripts/ver_linux b/scripts/ver_linux
new file mode 100755
index 000000000..00bdaf30d
--- /dev/null
+++ b/scripts/ver_linux
@@ -0,0 +1,97 @@
+#!/usr/bin/awk -f
+# SPDX-License-Identifier: GPL-2.0
+# Before running this script please ensure that your PATH is
+# typical as you use for compilation/installation. I use
+# /bin /sbin /usr/bin /usr/sbin /usr/local/bin, but it may
+# differ on your system.
+
+BEGIN {
+	usage = "If some fields are empty or look unusual you may have an old version.\n"
+	usage = usage "Compare to the current minimal requirements in Documentation/process/changes.rst\n"
+	print usage
+
+	system("uname -a")
+	printf("\n")
+
+	vernum = "[0-9]+([.]?[0-9]+)+"
+	libc = "libc[.]so[.][0-9]+$"
+	libcpp = "(libg|stdc)[+]+[.]so([.][0-9]+)+$"
+
+	printversion("bash", version("bash --version"))
+	printversion("bc", version("bc --version"))
+	printversion("bindgen", version("bindgen --version"))
+	printversion("binutils", version("ld -v"))
+	printversion("bison", version("bison --version"))
+	printversion("btrfs-progs", version("btrfs --version"))
+	printversion("Clang", version("clang --version"))
+	printversion("Console-tools", version("loadkeys -V"))
+	printversion("Dynamic linker (ldd)", version("ldd --version"))
+	printversion("e2fsprogs", version("e2fsck -V"))
+	printversion("flex", version("flex --version"))
+	printversion("gdb", version("gdb -version"))
+	printversion("GNU awk", version("gawk --version"))
+	printversion("GNU C", version("gcc -dumpversion"))
+	printversion("GNU make", version("make --version"))
+	printversion("GNU tar", version("tar --version"))
+	printversion("GRUB2", version("grub2-install --version"))
+	printversion("GRUB", version("grub-install --version"))
+	printversion("gtags", version("gtags --version"))
+	printversion("iptables", version("iptables -V"))
+	printversion("Isdn4k-utils", version("isdnctrl"))
+	printversion("jfsutils", version("fsck.jfs -V"))
+	printversion("Kbd", version("loadkeys -V"))
+	printversion("kmod", version("kmod -V"))
+
+	while ("ldconfig -p 2>/dev/null" | getline > 0)
+		if ($NF ~ libc || $NF ~ libcpp)
+			if (!seen[ver = version("readlink " $NF)]++)
+				printversion("Linux C" ($NF ~ libcpp? "++" : "") " Library", ver)
+
+	printversion("mcelog", version("mcelog --version"))
+	printversion("mkimage", version("mkimage --version"))
+	printversion("Module-init-tools", version("depmod -V"))
+	printversion("Mount", version("mount --version"))
+	printversion("Net-tools", version("ifconfig --version"))
+	printversion("nfs-utils", version("showmount --version"))
+	printversion("openssl", version("openssl version"))
+	printversion("pahole", version("pahole --version"))
+	printversion("Pcmcia-cs", version("cardmgr -V"))
+	printversion("pcmciautils", version("pccardctl -V"))
+	printversion("PPP", version("pppd --version"))
+	printversion("procps", version("ps --version"))
+	printversion("Python", version("python3 -V"))
+	printversion("quota-tools", version("quota -V"))
+	printversion("Rust", version("rustc --version"))
+	printversion("Sh-utils", version("expr --v"))
+	printversion("Sphinx", version("sphinx-build --version"))
+	printversion("squashfs-tools", version("mksquashfs -version"))
+	printversion("udev", version("udevadm --version"))
+	printversion("util-linux", version("mount --version"))
+	printversion("Wireless-tools", version("iwconfig --version"))
+	printversion("xfsprogs", version("xfs_db -V"))
+
+	while ("sort /proc/modules" | getline > 0) {
+		mods = mods sep $1
+		sep = " "
+	}
+	printversion("Modules Loaded", mods)
+}
+
+function version(cmd,    ver) {
+	cmd = cmd " 2>&1"
+	while (cmd | getline > 0) {
+		if (match($0, vernum)) {
+			ver = substr($0, RSTART, RLENGTH)
+			break
+		}
+	}
+	close(cmd)
+	return ver
+}
+
+function printversion(name, value,  ofmt) {
+	if (value != "") {
+		ofmt = "%-20s\t%s\n"
+		printf(ofmt, name, value)
+	}
+}