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, 304 insertions, 0 deletions

diff --git a/net/wireless/debugfs.c b/net/wireless/debugfs.c
new file mode 100644
index 000000000..f9e7fff1e
--- /dev/null
+++ b/net/wireless/debugfs.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * cfg80211 debugfs
+ *
+ * Copyright 2009	Luis R. Rodriguez <lrodriguez@atheros.com>
+ * Copyright 2007	Johannes Berg <johannes@sipsolutions.net>
+ * Copyright (C) 2023 Intel Corporation
+ */
+
+#include <linux/slab.h>
+#include "core.h"
+#include "debugfs.h"
+
+#define DEBUGFS_READONLY_FILE(name, buflen, fmt, value...)		\
+static ssize_t name## _read(struct file *file, char __user *userbuf,	\
+			    size_t count, loff_t *ppos)			\
+{									\
+	struct wiphy *wiphy = file->private_data;			\
+	char buf[buflen];						\
+	int res;							\
+									\
+	res = scnprintf(buf, buflen, fmt "\n", ##value);		\
+	return simple_read_from_buffer(userbuf, count, ppos, buf, res);	\
+}									\
+									\
+static const struct file_operations name## _ops = {			\
+	.read = name## _read,						\
+	.open = simple_open,						\
+	.llseek = generic_file_llseek,					\
+}
+
+#define DEBUGFS_RADIO_READONLY_FILE(name, buflen, fmt, value...)	\
+static ssize_t name## _read(struct file *file, char __user *userbuf,	\
+			    size_t count, loff_t *ppos)			\
+{									\
+	struct wiphy_radio_cfg *radio_cfg = file->private_data;		\
+	char buf[buflen];						\
+	int res;							\
+									\
+	res = scnprintf(buf, buflen, fmt "\n", ##value);		\
+	return simple_read_from_buffer(userbuf, count, ppos, buf, res);	\
+}									\
+									\
+static const struct file_operations name## _ops = {			\
+	.read = name## _read,						\
+	.open = simple_open,						\
+	.llseek = generic_file_llseek,					\
+}
+
+DEBUGFS_READONLY_FILE(rts_threshold, 20, "%d",
+		      wiphy->rts_threshold);
+DEBUGFS_READONLY_FILE(fragmentation_threshold, 20, "%d",
+		      wiphy->frag_threshold);
+DEBUGFS_READONLY_FILE(short_retry_limit, 20, "%d",
+		      wiphy->retry_short);
+DEBUGFS_READONLY_FILE(long_retry_limit, 20, "%d",
+		      wiphy->retry_long);
+
+DEBUGFS_RADIO_READONLY_FILE(radio_rts_threshold, 20, "%d",
+			    radio_cfg->rts_threshold);
+
+static int ht_print_chan(struct ieee80211_channel *chan,
+			 char *buf, int buf_size, int offset)
+{
+	if (WARN_ON(offset > buf_size))
+		return 0;
+
+	if (chan->flags & IEEE80211_CHAN_DISABLED)
+		return scnprintf(buf + offset,
+				 buf_size - offset,
+				 "%d Disabled\n",
+				 chan->center_freq);
+
+	return scnprintf(buf + offset,
+			 buf_size - offset,
+			 "%d HT40 %c%c\n",
+			 chan->center_freq,
+			 (chan->flags & IEEE80211_CHAN_NO_HT40MINUS) ?
+				' ' : '-',
+			 (chan->flags & IEEE80211_CHAN_NO_HT40PLUS) ?
+				' ' : '+');
+}
+
+static ssize_t ht40allow_map_read(struct file *file,
+				  char __user *user_buf,
+				  size_t count, loff_t *ppos)
+{
+	struct wiphy *wiphy = file->private_data;
+	char *buf;
+	unsigned int offset = 0, buf_size = PAGE_SIZE, i;
+	enum nl80211_band band;
+	struct ieee80211_supported_band *sband;
+	ssize_t r;
+
+	buf = kzalloc(buf_size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (band = 0; band < NUM_NL80211_BANDS; band++) {
+		sband = wiphy->bands[band];
+		if (!sband)
+			continue;
+		for (i = 0; i < sband->n_channels; i++)
+			offset += ht_print_chan(&sband->channels[i],
+						buf, buf_size, offset);
+	}
+
+	r = simple_read_from_buffer(user_buf, count, ppos, buf, offset);
+
+	kfree(buf);
+
+	return r;
+}
+
+static const struct file_operations ht40allow_map_ops = {
+	.read = ht40allow_map_read,
+	.open = simple_open,
+	.llseek = default_llseek,
+};
+
+#define DEBUGFS_ADD(name)						\
+	debugfs_create_file(#name, 0444, phyd, &rdev->wiphy, &name## _ops)
+
+#define DEBUGFS_RADIO_ADD(name, radio_idx)				\
+	debugfs_create_file(#name, 0444, radiod,			\
+			    &rdev->wiphy.radio_cfg[radio_idx],		\
+			    &name## _ops)
+
+void cfg80211_debugfs_rdev_add(struct cfg80211_registered_device *rdev)
+{
+	struct dentry *phyd = rdev->wiphy.debugfsdir;
+	struct dentry *radiod;
+	u8 i;
+
+	DEBUGFS_ADD(rts_threshold);
+	DEBUGFS_ADD(fragmentation_threshold);
+	DEBUGFS_ADD(short_retry_limit);
+	DEBUGFS_ADD(long_retry_limit);
+	DEBUGFS_ADD(ht40allow_map);
+
+	for (i = 0; i < rdev->wiphy.n_radio; i++) {
+		radiod = rdev->wiphy.radio_cfg[i].radio_debugfsdir;
+		DEBUGFS_RADIO_ADD(radio_rts_threshold, i);
+	}
+}
+
+struct debugfs_read_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t bufsize;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_read_work(struct wiphy *wiphy,
+					   struct wiphy_work *work)
+{
+	struct debugfs_read_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->bufsize, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_read_cancel(struct dentry *dentry,
+					     void *data)
+{
+	struct debugfs_read_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_read(struct wiphy *wiphy, struct file *file,
+				  char *buf, size_t bufsize,
+				  char __user *userbuf, size_t count,
+				  loff_t *ppos,
+				  ssize_t (*handler)(struct wiphy *wiphy,
+						     struct file *file,
+						     char *buf,
+						     size_t bufsize,
+						     void *data),
+				  void *data)
+{
+	struct debugfs_read_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.bufsize = bufsize,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_read_cancel,
+		.cancel_data = &work,
+	};
+
+	/* don't leak stack data or whatever */
+	memset(buf, 0, bufsize);
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_read_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	if (work.ret < 0)
+		return work.ret;
+
+	if (WARN_ON(work.ret > bufsize))
+		return -EINVAL;
+
+	return simple_read_from_buffer(userbuf, count, ppos, buf, work.ret);
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_read);
+
+struct debugfs_write_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t count;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_write_work(struct wiphy *wiphy,
+					    struct wiphy_work *work)
+{
+	struct debugfs_write_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->count, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_write_cancel(struct dentry *dentry,
+					      void *data)
+{
+	struct debugfs_write_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_write(struct wiphy *wiphy,
+				   struct file *file, char *buf, size_t bufsize,
+				   const char __user *userbuf, size_t count,
+				   ssize_t (*handler)(struct wiphy *wiphy,
+						      struct file *file,
+						      char *buf,
+						      size_t count,
+						      void *data),
+				   void *data)
+{
+	struct debugfs_write_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.count = count,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_write_cancel,
+		.cancel_data = &work,
+	};
+
+	/* mostly used for strings so enforce NUL-termination for safety */
+	if (count >= bufsize)
+		return -EINVAL;
+
+	memset(buf, 0, bufsize);
+
+	if (copy_from_user(buf, userbuf, count))
+		return -EFAULT;
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_write_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	return work.ret;
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_write);