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, 102 insertions, 0 deletions

diff --git a/include/sound/seq_kernel.h b/include/sound/seq_kernel.h
new file mode 100644
index 000000000..00c32eed2
--- /dev/null
+++ b/include/sound/seq_kernel.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_KERNEL_H
+#define __SOUND_SEQ_KERNEL_H
+
+/*
+ *  Main kernel header file for the ALSA sequencer
+ *  Copyright (c) 1998 by Frank van de Pol <fvdpol@coil.demon.nl>
+ */
+#include <linux/time.h>
+#include <sound/asequencer.h>
+
+typedef struct snd_seq_real_time snd_seq_real_time_t;
+typedef union snd_seq_timestamp snd_seq_timestamp_t;
+
+/* maximum number of queues */
+#define SNDRV_SEQ_MAX_QUEUES		32
+
+/* max number of concurrent clients */
+#define SNDRV_SEQ_MAX_CLIENTS 		192
+
+/* max number of concurrent ports */
+#define SNDRV_SEQ_MAX_PORTS 		254
+
+/* max number of events in memory pool */
+#define SNDRV_SEQ_MAX_EVENTS		2000
+
+/* default number of events in memory pool */
+#define SNDRV_SEQ_DEFAULT_EVENTS	500
+
+/* max number of events in memory pool for one client (outqueue) */
+#define SNDRV_SEQ_MAX_CLIENT_EVENTS	2000
+
+/* default number of events in memory pool for one client (outqueue) */
+#define SNDRV_SEQ_DEFAULT_CLIENT_EVENTS	200
+
+/* max delivery path length */
+/* NOTE: this shouldn't be greater than MAX_LOCKDEP_SUBCLASSES */
+#define SNDRV_SEQ_MAX_HOPS		8
+
+/* max size of event size */
+#define SNDRV_SEQ_MAX_EVENT_LEN		0x3fffffff
+
+/* call-backs for kernel port */
+struct snd_seq_port_callback {
+	struct module *owner;
+	void *private_data;
+	int (*subscribe)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*unsubscribe)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*use)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*unuse)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*event_input)(struct snd_seq_event *ev, int direct, void *private_data, int atomic, int hop);
+	void (*private_free)(void *private_data);
+	/*...*/
+};
+
+/* interface for kernel client */
+__printf(3, 4)
+int snd_seq_create_kernel_client(struct snd_card *card, int client_index,
+				 const char *name_fmt, ...);
+int snd_seq_delete_kernel_client(int client);
+int snd_seq_kernel_client_enqueue(int client, struct snd_seq_event *ev,
+				  struct file *file, bool blocking);
+int snd_seq_kernel_client_dispatch(int client, struct snd_seq_event *ev, int atomic, int hop);
+int snd_seq_kernel_client_ctl(int client, unsigned int cmd, void *arg);
+
+#define SNDRV_SEQ_EXT_MASK	0xc0000000
+#define SNDRV_SEQ_EXT_USRPTR	0x80000000
+#define SNDRV_SEQ_EXT_CHAINED	0x40000000
+
+typedef int (*snd_seq_dump_func_t)(void *ptr, void *buf, int count);
+int snd_seq_expand_var_event(const struct snd_seq_event *event, int count, char *buf,
+			     int in_kernel, int size_aligned);
+int snd_seq_expand_var_event_at(const struct snd_seq_event *event, int count,
+				char *buf, int offset);
+int snd_seq_dump_var_event(const struct snd_seq_event *event,
+			   snd_seq_dump_func_t func, void *private_data);
+
+/* size of the event packet; it can be greater than snd_seq_event size */
+static inline size_t snd_seq_event_packet_size(struct snd_seq_event *ev)
+{
+	if (snd_seq_ev_is_ump(ev))
+		return sizeof(struct snd_seq_ump_event);
+	return sizeof(struct snd_seq_event);
+}
+
+/* interface for OSS emulation */
+int snd_seq_set_queue_tempo(int client, struct snd_seq_queue_tempo *tempo);
+
+/* port attach/detach */
+int snd_seq_event_port_attach(int client, struct snd_seq_port_callback *pcbp,
+			      int cap, int type, int midi_channels, int midi_voices, char *portname);
+int snd_seq_event_port_detach(int client, int port);
+
+#ifdef CONFIG_MODULES
+void snd_seq_autoload_init(void);
+void snd_seq_autoload_exit(void);
+#else
+#define snd_seq_autoload_init()
+#define snd_seq_autoload_exit()
+#endif
+
+#endif /* __SOUND_SEQ_KERNEL_H */