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, 53 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-chromeos b/Documentation/ABI/testing/sysfs-class-chromeos
new file mode 100644
index 000000000..7fa5be6cc
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-chromeos
@@ -0,0 +1,53 @@
+What:		/sys/class/chromeos/<ec-device-name>/flashinfo
+Date:		August 2015
+KernelVersion:	4.2
+Description:
+		Show the EC flash information.
+
+What:		/sys/class/chromeos/<ec-device-name>/kb_wake_angle
+Date:		March 2018
+KernelVersion:	4.17
+Description:
+		Control the keyboard wake lid angle. Values are between
+		0 and 360. This file will also show the keyboard wake lid
+		angle by querying the hardware.
+
+What:		/sys/class/chromeos/<ec-device-name>/reboot
+Date:		August 2015
+KernelVersion:	4.2
+Description:
+		Tell the EC to reboot in various ways. Options are:
+
+		- "cancel": Cancel a pending reboot.
+		- "ro": Jump to RO without rebooting.
+		- "rw": Jump to RW without rebooting.
+		- "cold": Cold reboot.
+		- "disable-jump": Disable jump until next reboot.
+		- "hibernate": Hibernate the EC.
+		- "at-shutdown": Reboot after an AP shutdown.
+
+What:		/sys/class/chromeos/<ec-device-name>/version
+Date:		August 2015
+KernelVersion:	4.2
+Description:
+		Show the information about the EC software and hardware.
+
+What:		/sys/class/chromeos/cros_ec/usbpdmuxinfo
+Date:		February 2025
+Description:
+		Show PD mux status for each typec port with following flags:
+		- "USB": USB connected
+		- "DP": DP connected
+		- "POLARITY": CC line Polarity inverted
+		- "HPD_IRQ": Hot Plug Detect interrupt is asserted
+		- "HPD_LVL": Hot Plug Detect level is asserted
+		- "SAFE": DP is in safe mode
+		- "TBT": TBT enabled
+		- "USB4": USB4 enabled
+
+What:		/sys/class/chromeos/cros_ec/ap_mode_entry
+Date:		February 2025
+Description:
+		Show if the AP mode entry EC feature is supported.
+		It indicates whether the EC waits for direction from the AP
+		to enter Type-C altmodes or USB4 mode.