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, 142 insertions, 0 deletions

diff --git a/drivers/md/bcache/sysfs.h b/drivers/md/bcache/sysfs.h
new file mode 100644
index 000000000..65b8bd975
--- /dev/null
+++ b/drivers/md/bcache/sysfs.h
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHE_SYSFS_H_
+#define _BCACHE_SYSFS_H_
+
+#define KTYPE(type)							\
+const struct kobj_type type ## _ktype = {					\
+	.release	= type ## _release,				\
+	.sysfs_ops	= &((const struct sysfs_ops) {			\
+		.show	= type ## _show,				\
+		.store	= type ## _store				\
+	}),								\
+	.default_groups	= type ## _groups				\
+}
+
+#define SHOW(fn)							\
+static ssize_t fn ## _show(struct kobject *kobj, struct attribute *attr,\
+			   char *buf)					\
+
+#define STORE(fn)							\
+static ssize_t fn ## _store(struct kobject *kobj, struct attribute *attr,\
+			    const char *buf, size_t size)		\
+
+#define SHOW_LOCKED(fn)							\
+SHOW(fn)								\
+{									\
+	ssize_t ret;							\
+	mutex_lock(&bch_register_lock);					\
+	ret = __ ## fn ## _show(kobj, attr, buf);			\
+	mutex_unlock(&bch_register_lock);				\
+	return ret;							\
+}
+
+#define STORE_LOCKED(fn)						\
+STORE(fn)								\
+{									\
+	ssize_t ret;							\
+	mutex_lock(&bch_register_lock);					\
+	ret = __ ## fn ## _store(kobj, attr, buf, size);		\
+	mutex_unlock(&bch_register_lock);				\
+	return ret;							\
+}
+
+#define __sysfs_attribute(_name, _mode)					\
+	static struct attribute sysfs_##_name =				\
+		{ .name = #_name, .mode = _mode }
+
+#define write_attribute(n)	__sysfs_attribute(n, 0200)
+#define read_attribute(n)	__sysfs_attribute(n, 0444)
+#define rw_attribute(n)		__sysfs_attribute(n, 0644)
+
+#define sysfs_printf(file, fmt, ...)					\
+do {									\
+	if (attr == &sysfs_ ## file)					\
+		return sysfs_emit(buf, fmt "\n", __VA_ARGS__);	\
+} while (0)
+
+#define sysfs_print(file, var)						\
+do {									\
+	if (attr == &sysfs_ ## file)					\
+		return sysfs_emit(buf,						\
+				__builtin_types_compatible_p(typeof(var), int)		\
+					 ? "%i\n" :				\
+				__builtin_types_compatible_p(typeof(var), unsigned int)	\
+					 ? "%u\n" :				\
+				__builtin_types_compatible_p(typeof(var), long)		\
+					 ? "%li\n" :			\
+				__builtin_types_compatible_p(typeof(var), unsigned long)\
+					 ? "%lu\n" :			\
+				__builtin_types_compatible_p(typeof(var), int64_t)	\
+					 ? "%lli\n" :			\
+				__builtin_types_compatible_p(typeof(var), uint64_t)	\
+					 ? "%llu\n" :			\
+				__builtin_types_compatible_p(typeof(var), const char *)	\
+					 ? "%s\n" : "%i\n", var);	\
+} while (0)
+
+#define sysfs_hprint(file, val)						\
+do {									\
+	if (attr == &sysfs_ ## file) {					\
+		ssize_t ret = bch_hprint(buf, val);			\
+		strcat(buf, "\n");					\
+		return ret + 1;						\
+	}								\
+} while (0)
+
+#define var_printf(_var, fmt)	sysfs_printf(_var, fmt, var(_var))
+#define var_print(_var)		sysfs_print(_var, var(_var))
+#define var_hprint(_var)	sysfs_hprint(_var, var(_var))
+
+#define sysfs_strtoul(file, var)					\
+do {									\
+	if (attr == &sysfs_ ## file)					\
+		return strtoul_safe(buf, var) ?: (ssize_t) size;	\
+} while (0)
+
+#define sysfs_strtoul_bool(file, var)					\
+do {									\
+	if (attr == &sysfs_ ## file) {					\
+		unsigned long v = strtoul_or_return(buf);		\
+									\
+		var = v ? 1 : 0;					\
+		return size;						\
+	}								\
+} while (0)
+
+#define sysfs_strtoul_clamp(file, var, min, max)			\
+do {									\
+	if (attr == &sysfs_ ## file) {					\
+		unsigned long v = 0;					\
+		ssize_t ret;						\
+		ret = strtoul_safe_clamp(buf, v, min, max);		\
+		if (!ret) {						\
+			var = v;					\
+			return size;					\
+		}							\
+		return ret;						\
+	}								\
+} while (0)
+
+#define strtoul_or_return(cp)						\
+({									\
+	unsigned long _v;						\
+	int _r = kstrtoul(cp, 10, &_v);					\
+	if (_r)								\
+		return _r;						\
+	_v;								\
+})
+
+#define strtoi_h_or_return(cp, v)					\
+do {									\
+	int _r = strtoi_h(cp, &v);					\
+	if (_r)								\
+		return _r;						\
+} while (0)
+
+#define sysfs_hatoi(file, var)						\
+do {									\
+	if (attr == &sysfs_ ## file)					\
+		return strtoi_h(buf, &var) ?: (ssize_t) size;		\
+} while (0)
+
+#endif  /* _BCACHE_SYSFS_H_ */