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, 47 insertions, 0 deletions

diff --git a/samples/Makefile b/samples/Makefile
new file mode 100644
index 000000000..07641e177
--- /dev/null
+++ b/samples/Makefile
@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for Linux samples code
+
+subdir-$(CONFIG_SAMPLE_AUXDISPLAY)	+= auxdisplay
+subdir-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs
+subdir-$(CONFIG_SAMPLE_CHECK_EXEC)	+= check-exec
+subdir-$(CONFIG_SAMPLE_CGROUP) += cgroup
+obj-$(CONFIG_SAMPLE_CONFIGFS)		+= configfs/
+obj-$(CONFIG_SAMPLE_CONNECTOR)		+= connector/
+obj-$(CONFIG_SAMPLE_FANOTIFY_ERROR)	+= fanotify/
+subdir-$(CONFIG_SAMPLE_HIDRAW)		+= hidraw
+obj-$(CONFIG_SAMPLE_HW_BREAKPOINT)	+= hw_breakpoint/
+obj-$(CONFIG_SAMPLE_KDB)		+= kdb/
+obj-$(CONFIG_SAMPLE_KFIFO)		+= kfifo/
+obj-$(CONFIG_SAMPLE_KOBJECT)		+= kobject/
+obj-$(CONFIG_SAMPLE_KPROBES)		+= kprobes/
+subdir-$(CONFIG_SAMPLE_LANDLOCK)	+= landlock
+obj-$(CONFIG_SAMPLE_LIVEPATCH)		+= livepatch/
+subdir-$(CONFIG_SAMPLE_PIDFD)		+= pidfd
+obj-$(CONFIG_SAMPLE_QMI_CLIENT)		+= qmi/
+obj-$(CONFIG_SAMPLE_RPMSG_CLIENT)	+= rpmsg/
+subdir-$(CONFIG_SAMPLE_SECCOMP)		+= seccomp
+subdir-$(CONFIG_SAMPLE_TIMER)		+= timers
+obj-$(CONFIG_SAMPLE_TRACE_EVENTS)	+= trace_events/
+obj-$(CONFIG_SAMPLE_TRACE_CUSTOM_EVENTS) += trace_events/
+obj-$(CONFIG_SAMPLE_TRACE_PRINTK)	+= trace_printk/
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT)	+= ftrace/
+obj-$(CONFIG_SAMPLE_FTRACE_DIRECT_MULTI) += ftrace/
+obj-$(CONFIG_SAMPLE_FTRACE_OPS)		+= ftrace/
+obj-$(CONFIG_SAMPLE_TRACE_ARRAY)	+= ftrace/
+subdir-$(CONFIG_SAMPLE_UHID)		+= uhid
+obj-$(CONFIG_VIDEO_PCI_SKELETON)	+= v4l/
+obj-y					+= vfio-mdev/
+subdir-$(CONFIG_SAMPLE_VFS)		+= vfs
+obj-$(CONFIG_SAMPLE_INTEL_MEI)		+= mei/
+obj-$(CONFIG_SAMPLE_TPS6594_PFSM)	+= pfsm/
+subdir-$(CONFIG_SAMPLE_WATCHDOG)	+= watchdog
+subdir-$(CONFIG_SAMPLE_WATCH_QUEUE)	+= watch_queue
+obj-$(CONFIG_SAMPLE_KMEMLEAK)		+= kmemleak/
+obj-$(CONFIG_SAMPLE_CORESIGHT_SYSCFG)	+= coresight/
+obj-$(CONFIG_SAMPLE_FPROBE)		+= fprobe/
+obj-$(CONFIG_SAMPLES_RUST)		+= rust/
+obj-$(CONFIG_SAMPLE_DAMON_WSSE)		+= damon/
+obj-$(CONFIG_SAMPLE_DAMON_PRCL)		+= damon/
+obj-$(CONFIG_SAMPLE_DAMON_MTIER)	+= damon/
+obj-$(CONFIG_SAMPLE_HUNG_TASK)		+= hung_task/
+obj-$(CONFIG_SAMPLE_TSM_MR)		+= tsm-mr/