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, 144 insertions, 0 deletions

diff --git a/net/mac802154/mac_cmd.c b/net/mac802154/mac_cmd.c
new file mode 100644
index 000000000..8ea5b6402
--- /dev/null
+++ b/net/mac802154/mac_cmd.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MAC commands interface
+ *
+ * Copyright 2007-2012 Siemens AG
+ *
+ * Written by:
+ * Sergey Lapin <slapin@ossfans.org>
+ * Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
+ * Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
+ */
+
+#include <linux/skbuff.h>
+#include <linux/if_arp.h>
+#include <linux/ieee802154.h>
+
+#include <net/ieee802154_netdev.h>
+#include <net/cfg802154.h>
+#include <net/mac802154.h>
+
+#include "ieee802154_i.h"
+#include "driver-ops.h"
+
+static int mac802154_mlme_start_req(struct net_device *dev,
+				    struct ieee802154_addr *addr,
+				    u8 channel, u8 page,
+				    u8 bcn_ord, u8 sf_ord,
+				    u8 pan_coord, u8 blx,
+				    u8 coord_realign)
+{
+	struct ieee802154_llsec_params params;
+	int changed = 0;
+
+	ASSERT_RTNL();
+
+	BUG_ON(addr->mode != IEEE802154_ADDR_SHORT);
+
+	dev->ieee802154_ptr->pan_id = addr->pan_id;
+	dev->ieee802154_ptr->short_addr = addr->short_addr;
+	mac802154_dev_set_page_channel(dev, page, channel);
+
+	params.pan_id = addr->pan_id;
+	changed |= IEEE802154_LLSEC_PARAM_PAN_ID;
+
+	params.hwaddr = ieee802154_devaddr_from_raw(dev->dev_addr);
+	changed |= IEEE802154_LLSEC_PARAM_HWADDR;
+
+	params.coord_hwaddr = params.hwaddr;
+	changed |= IEEE802154_LLSEC_PARAM_COORD_HWADDR;
+
+	params.coord_shortaddr = addr->short_addr;
+	changed |= IEEE802154_LLSEC_PARAM_COORD_SHORTADDR;
+
+	return mac802154_set_params(dev, &params, changed);
+}
+
+static int mac802154_set_mac_params(struct net_device *dev,
+				    const struct ieee802154_mac_params *params)
+{
+	struct ieee802154_sub_if_data *sdata = IEEE802154_DEV_TO_SUB_IF(dev);
+	struct ieee802154_local *local = sdata->local;
+	struct wpan_dev *wpan_dev = &sdata->wpan_dev;
+	int ret;
+
+	ASSERT_RTNL();
+
+	/* PHY */
+	wpan_dev->wpan_phy->transmit_power = params->transmit_power;
+	wpan_dev->wpan_phy->cca = params->cca;
+	wpan_dev->wpan_phy->cca_ed_level = params->cca_ed_level;
+
+	/* MAC */
+	wpan_dev->min_be = params->min_be;
+	wpan_dev->max_be = params->max_be;
+	wpan_dev->csma_retries = params->csma_retries;
+	wpan_dev->frame_retries = params->frame_retries;
+	wpan_dev->lbt = params->lbt;
+
+	if (local->hw.phy->flags & WPAN_PHY_FLAG_TXPOWER) {
+		ret = drv_set_tx_power(local, params->transmit_power);
+		if (ret < 0)
+			return ret;
+	}
+
+	if (local->hw.phy->flags & WPAN_PHY_FLAG_CCA_MODE) {
+		ret = drv_set_cca_mode(local, &params->cca);
+		if (ret < 0)
+			return ret;
+	}
+
+	if (local->hw.phy->flags & WPAN_PHY_FLAG_CCA_ED_LEVEL) {
+		ret = drv_set_cca_ed_level(local, params->cca_ed_level);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+static void mac802154_get_mac_params(struct net_device *dev,
+				     struct ieee802154_mac_params *params)
+{
+	struct ieee802154_sub_if_data *sdata = IEEE802154_DEV_TO_SUB_IF(dev);
+	struct wpan_dev *wpan_dev = &sdata->wpan_dev;
+
+	ASSERT_RTNL();
+
+	/* PHY */
+	params->transmit_power = wpan_dev->wpan_phy->transmit_power;
+	params->cca = wpan_dev->wpan_phy->cca;
+	params->cca_ed_level = wpan_dev->wpan_phy->cca_ed_level;
+
+	/* MAC */
+	params->min_be = wpan_dev->min_be;
+	params->max_be = wpan_dev->max_be;
+	params->csma_retries = wpan_dev->csma_retries;
+	params->frame_retries = wpan_dev->frame_retries;
+	params->lbt = wpan_dev->lbt;
+}
+
+static const struct ieee802154_llsec_ops mac802154_llsec_ops = {
+	.get_params = mac802154_get_params,
+	.set_params = mac802154_set_params,
+	.add_key = mac802154_add_key,
+	.del_key = mac802154_del_key,
+	.add_dev = mac802154_add_dev,
+	.del_dev = mac802154_del_dev,
+	.add_devkey = mac802154_add_devkey,
+	.del_devkey = mac802154_del_devkey,
+	.add_seclevel = mac802154_add_seclevel,
+	.del_seclevel = mac802154_del_seclevel,
+	.lock_table = mac802154_lock_table,
+	.get_table = mac802154_get_table,
+	.unlock_table = mac802154_unlock_table,
+};
+
+struct ieee802154_mlme_ops mac802154_mlme_wpan = {
+	.start_req = mac802154_mlme_start_req,
+
+	.llsec = &mac802154_llsec_ops,
+
+	.set_mac_params = mac802154_set_mac_params,
+	.get_mac_params = mac802154_get_mac_params,
+};