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/mm/damon/modules-common.h b/mm/damon/modules-common.h
new file mode 100644
index 000000000..6fd45490e
--- /dev/null
+++ b/mm/damon/modules-common.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common Code for DAMON Modules
+ */
+
+#include <linux/moduleparam.h>
+
+#define DEFINE_DAMON_MODULES_MON_ATTRS_PARAMS(attrs)			\
+	module_param_named(sample_interval, attrs.sample_interval,	\
+			ulong, 0600);					\
+	module_param_named(aggr_interval, attrs.aggr_interval, ulong,	\
+			0600);						\
+	module_param_named(min_nr_regions, attrs.min_nr_regions, ulong,	\
+			0600);						\
+	module_param_named(max_nr_regions, attrs.max_nr_regions, ulong,	\
+			0600);
+
+#define DEFINE_DAMON_MODULES_DAMOS_TIME_QUOTA(quota)			\
+	module_param_named(quota_ms, quota.ms, ulong, 0600);		\
+	module_param_named(quota_reset_interval_ms,			\
+			quota.reset_interval, ulong, 0600);
+
+#define DEFINE_DAMON_MODULES_DAMOS_QUOTAS(quota)			\
+	DEFINE_DAMON_MODULES_DAMOS_TIME_QUOTA(quota)			\
+	module_param_named(quota_sz, quota.sz, ulong, 0600);
+
+#define DEFINE_DAMON_MODULES_WMARKS_PARAMS(wmarks)			\
+	module_param_named(wmarks_interval, wmarks.interval, ulong,	\
+			0600);						\
+	module_param_named(wmarks_high, wmarks.high, ulong, 0600);	\
+	module_param_named(wmarks_mid, wmarks.mid, ulong, 0600);	\
+	module_param_named(wmarks_low, wmarks.low, ulong, 0600);
+
+#define DEFINE_DAMON_MODULES_DAMOS_STATS_PARAMS(stat, try_name,		\
+		succ_name, qt_exceed_name)				\
+	module_param_named(nr_##try_name, stat.nr_tried, ulong, 0400);	\
+	module_param_named(bytes_##try_name, stat.sz_tried, ulong,	\
+			0400);						\
+	module_param_named(nr_##succ_name, stat.nr_applied, ulong,	\
+			0400);						\
+	module_param_named(bytes_##succ_name, stat.sz_applied, ulong,	\
+			0400);						\
+	module_param_named(nr_##qt_exceed_name, stat.qt_exceeds, ulong,	\
+			0400);
+
+int damon_modules_new_paddr_ctx_target(struct damon_ctx **ctxp,
+		struct damon_target **targetp);