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, 48 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-s3c.h b/drivers/rtc/rtc-s3c.h
new file mode 100644
index 000000000..11d7a1255
--- /dev/null
+++ b/drivers/rtc/rtc-s3c.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2003 Simtec Electronics <linux@simtec.co.uk>
+ *		      http://www.simtec.co.uk/products/SWLINUX/
+ *
+ * S3C2410 Internal RTC register definition
+*/
+
+#ifndef __ASM_ARCH_REGS_RTC_H
+#define __ASM_ARCH_REGS_RTC_H __FILE__
+
+#define S3C2410_RTCREG(x) (x)
+#define S3C2410_INTP		S3C2410_RTCREG(0x30)
+#define S3C2410_INTP_ALM	(1 << 1)
+#define S3C2410_INTP_TIC	(1 << 0)
+
+#define S3C2410_RTCCON		S3C2410_RTCREG(0x40)
+#define S3C2410_RTCCON_RTCEN	(1 << 0)
+#define S3C2410_RTCCON_CNTSEL	(1 << 2)
+#define S3C2410_RTCCON_CLKRST	(1 << 3)
+#define S3C2443_RTCCON_TICSEL	(1 << 4)
+#define S3C64XX_RTCCON_TICEN	(1 << 8)
+
+#define S3C2410_RTCALM		S3C2410_RTCREG(0x50)
+#define S3C2410_RTCALM_ALMEN	(1 << 6)
+#define S3C2410_RTCALM_YEAREN	(1 << 5)
+#define S3C2410_RTCALM_MONEN	(1 << 4)
+#define S3C2410_RTCALM_DAYEN	(1 << 3)
+#define S3C2410_RTCALM_HOUREN	(1 << 2)
+#define S3C2410_RTCALM_MINEN	(1 << 1)
+#define S3C2410_RTCALM_SECEN	(1 << 0)
+
+#define S3C2410_ALMSEC		S3C2410_RTCREG(0x54)
+#define S3C2410_ALMMIN		S3C2410_RTCREG(0x58)
+#define S3C2410_ALMHOUR		S3C2410_RTCREG(0x5c)
+
+#define S3C2410_ALMDATE		S3C2410_RTCREG(0x60)
+#define S3C2410_ALMMON		S3C2410_RTCREG(0x64)
+#define S3C2410_ALMYEAR		S3C2410_RTCREG(0x68)
+
+#define S3C2410_RTCSEC		S3C2410_RTCREG(0x70)
+#define S3C2410_RTCMIN		S3C2410_RTCREG(0x74)
+#define S3C2410_RTCHOUR		S3C2410_RTCREG(0x78)
+#define S3C2410_RTCDATE		S3C2410_RTCREG(0x7c)
+#define S3C2410_RTCMON		S3C2410_RTCREG(0x84)
+#define S3C2410_RTCYEAR		S3C2410_RTCREG(0x88)
+
+#endif /* __ASM_ARCH_REGS_RTC_H */