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, 454 insertions, 0 deletions

diff --git a/drivers/bluetooth/virtio_bt.c b/drivers/bluetooth/virtio_bt.c
new file mode 100644
index 000000000..c20d54088
--- /dev/null
+++ b/drivers/bluetooth/virtio_bt.c
@@ -0,0 +1,454 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/module.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/skbuff.h>
+
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_bt.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#define VERSION "0.1"
+#define VIRTBT_RX_BUF_SIZE 1000
+
+enum {
+	VIRTBT_VQ_TX,
+	VIRTBT_VQ_RX,
+	VIRTBT_NUM_VQS,
+};
+
+struct virtio_bluetooth {
+	struct virtio_device *vdev;
+	struct virtqueue *vqs[VIRTBT_NUM_VQS];
+	struct work_struct rx;
+	struct hci_dev *hdev;
+};
+
+static int virtbt_add_inbuf(struct virtio_bluetooth *vbt)
+{
+	struct virtqueue *vq = vbt->vqs[VIRTBT_VQ_RX];
+	struct scatterlist sg[1];
+	struct sk_buff *skb;
+	int err;
+
+	skb = alloc_skb(VIRTBT_RX_BUF_SIZE, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
+	sg_init_one(sg, skb->data, VIRTBT_RX_BUF_SIZE);
+
+	err = virtqueue_add_inbuf(vq, sg, 1, skb, GFP_KERNEL);
+	if (err < 0) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	return 0;
+}
+
+static int virtbt_open(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_open_vdev(struct virtio_bluetooth *vbt)
+{
+	if (virtbt_add_inbuf(vbt) < 0)
+		return -EIO;
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_RX]);
+	return 0;
+}
+
+static int virtbt_close(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_close_vdev(struct virtio_bluetooth *vbt)
+{
+	int i;
+
+	cancel_work_sync(&vbt->rx);
+
+	for (i = 0; i < ARRAY_SIZE(vbt->vqs); i++) {
+		struct virtqueue *vq = vbt->vqs[i];
+		struct sk_buff *skb;
+
+		while ((skb = virtqueue_detach_unused_buf(vq)))
+			kfree_skb(skb);
+		cond_resched();
+	}
+
+	return 0;
+}
+
+static int virtbt_flush(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	struct virtio_bluetooth *vbt = hci_get_drvdata(hdev);
+	struct scatterlist sg[1];
+	int err;
+
+	memcpy(skb_push(skb, 1), &hci_skb_pkt_type(skb), 1);
+
+	sg_init_one(sg, skb->data, skb->len);
+	err = virtqueue_add_outbuf(vbt->vqs[VIRTBT_VQ_TX], sg, 1, skb,
+				   GFP_KERNEL);
+	if (err) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_TX]);
+	return 0;
+}
+
+static int virtbt_setup_zephyr(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Read Build Information */
+	skb = __hci_cmd_sync(hdev, 0xfc08, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	/* Bounded print: the backend controls skb->len. */
+	if (skb->len > 1) {
+		int len = skb->len - 1;
+
+		bt_dev_info(hdev, "%.*s", len, (char *)(skb->data + 1));
+		hci_set_fw_info(hdev, "%.*s", len, skb->data + 1);
+	}
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_set_bdaddr_zephyr(struct hci_dev *hdev,
+				    const bdaddr_t *bdaddr)
+{
+	struct sk_buff *skb;
+
+	/* Write BD_ADDR */
+	skb = __hci_cmd_sync(hdev, 0xfc06, 6, bdaddr, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_setup_intel(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Intel Read Version */
+	skb = __hci_cmd_sync(hdev, 0xfc05, 0, NULL, HCI_CMD_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_set_bdaddr_intel(struct hci_dev *hdev, const bdaddr_t *bdaddr)
+{
+	struct sk_buff *skb;
+
+	/* Intel Write BD Address */
+	skb = __hci_cmd_sync(hdev, 0xfc31, 6, bdaddr, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_setup_realtek(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Read ROM Version */
+	skb = __hci_cmd_sync(hdev, 0xfc6d, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	bt_dev_info(hdev, "ROM version %u", *((__u8 *) (skb->data + 1)));
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_shutdown_generic(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Reset */
+	skb = __hci_cmd_sync(hdev, HCI_OP_RESET, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static void virtbt_rx_handle(struct virtio_bluetooth *vbt, struct sk_buff *skb)
+{
+	size_t min_hdr;
+	__u8 pkt_type;
+
+	pkt_type = *((__u8 *) skb->data);
+	skb_pull(skb, 1);
+
+	switch (pkt_type) {
+	case HCI_EVENT_PKT:
+		min_hdr = sizeof(struct hci_event_hdr);
+		break;
+	case HCI_ACLDATA_PKT:
+		min_hdr = sizeof(struct hci_acl_hdr);
+		break;
+	case HCI_SCODATA_PKT:
+		min_hdr = sizeof(struct hci_sco_hdr);
+		break;
+	case HCI_ISODATA_PKT:
+		min_hdr = sizeof(struct hci_iso_hdr);
+		break;
+	default:
+		kfree_skb(skb);
+		return;
+	}
+
+	if (skb->len < min_hdr) {
+		bt_dev_err_ratelimited(vbt->hdev,
+				       "rx pkt_type 0x%02x payload %u < hdr %zu\n",
+				       pkt_type, skb->len, min_hdr);
+		kfree_skb(skb);
+		return;
+	}
+
+	hci_skb_pkt_type(skb) = pkt_type;
+	hci_recv_frame(vbt->hdev, skb);
+}
+
+static void virtbt_rx_work(struct work_struct *work)
+{
+	struct virtio_bluetooth *vbt = container_of(work,
+						    struct virtio_bluetooth, rx);
+	struct sk_buff *skb;
+	unsigned int len;
+
+	skb = virtqueue_get_buf(vbt->vqs[VIRTBT_VQ_RX], &len);
+	if (!skb)
+		return;
+
+	if (!len || len > VIRTBT_RX_BUF_SIZE) {
+		bt_dev_err_ratelimited(vbt->hdev,
+				       "rx reply len %u outside [1, %u]\n",
+				       len, VIRTBT_RX_BUF_SIZE);
+		kfree_skb(skb);
+	} else {
+		skb_put(skb, len);
+		virtbt_rx_handle(vbt, skb);
+	}
+
+	if (virtbt_add_inbuf(vbt) < 0)
+		return;
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_RX]);
+}
+
+static void virtbt_tx_done(struct virtqueue *vq)
+{
+	struct sk_buff *skb;
+	unsigned int len;
+
+	while ((skb = virtqueue_get_buf(vq, &len)))
+		kfree_skb(skb);
+}
+
+static void virtbt_rx_done(struct virtqueue *vq)
+{
+	struct virtio_bluetooth *vbt = vq->vdev->priv;
+
+	schedule_work(&vbt->rx);
+}
+
+static int virtbt_probe(struct virtio_device *vdev)
+{
+	struct virtqueue_info vqs_info[VIRTBT_NUM_VQS] = {
+		[VIRTBT_VQ_TX] = { "tx", virtbt_tx_done },
+		[VIRTBT_VQ_RX] = { "rx", virtbt_rx_done },
+	};
+	struct virtio_bluetooth *vbt;
+	struct hci_dev *hdev;
+	int err;
+	__u8 type;
+
+	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
+		return -ENODEV;
+
+	type = virtio_cread8(vdev, offsetof(struct virtio_bt_config, type));
+
+	switch (type) {
+	case VIRTIO_BT_CONFIG_TYPE_PRIMARY:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	vbt = kzalloc_obj(*vbt);
+	if (!vbt)
+		return -ENOMEM;
+
+	vdev->priv = vbt;
+	vbt->vdev = vdev;
+
+	INIT_WORK(&vbt->rx, virtbt_rx_work);
+
+	err = virtio_find_vqs(vdev, VIRTBT_NUM_VQS, vbt->vqs, vqs_info, NULL);
+	if (err)
+		return err;
+
+	hdev = hci_alloc_dev();
+	if (!hdev) {
+		err = -ENOMEM;
+		goto failed;
+	}
+
+	vbt->hdev = hdev;
+
+	hdev->bus = HCI_VIRTIO;
+	hci_set_drvdata(hdev, vbt);
+
+	hdev->open  = virtbt_open;
+	hdev->close = virtbt_close;
+	hdev->flush = virtbt_flush;
+	hdev->send  = virtbt_send_frame;
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_VND_HCI)) {
+		__u16 vendor;
+
+		if (virtio_has_feature(vdev, VIRTIO_BT_F_CONFIG_V2))
+			virtio_cread(vdev, struct virtio_bt_config_v2,
+				     vendor, &vendor);
+		else
+			virtio_cread(vdev, struct virtio_bt_config,
+				     vendor, &vendor);
+
+		switch (vendor) {
+		case VIRTIO_BT_CONFIG_VENDOR_ZEPHYR:
+			hdev->manufacturer = 1521;
+			hdev->setup = virtbt_setup_zephyr;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hdev->set_bdaddr = virtbt_set_bdaddr_zephyr;
+			break;
+
+		case VIRTIO_BT_CONFIG_VENDOR_INTEL:
+			hdev->manufacturer = 2;
+			hdev->setup = virtbt_setup_intel;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hdev->set_bdaddr = virtbt_set_bdaddr_intel;
+			hci_set_quirk(hdev, HCI_QUIRK_STRICT_DUPLICATE_FILTER);
+			hci_set_quirk(hdev, HCI_QUIRK_SIMULTANEOUS_DISCOVERY);
+			hci_set_quirk(hdev, HCI_QUIRK_WIDEBAND_SPEECH_SUPPORTED);
+			break;
+
+		case VIRTIO_BT_CONFIG_VENDOR_REALTEK:
+			hdev->manufacturer = 93;
+			hdev->setup = virtbt_setup_realtek;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hci_set_quirk(hdev, HCI_QUIRK_SIMULTANEOUS_DISCOVERY);
+			hci_set_quirk(hdev, HCI_QUIRK_WIDEBAND_SPEECH_SUPPORTED);
+			break;
+		}
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_MSFT_EXT)) {
+		__u16 msft_opcode;
+
+		if (virtio_has_feature(vdev, VIRTIO_BT_F_CONFIG_V2))
+			virtio_cread(vdev, struct virtio_bt_config_v2,
+				     msft_opcode, &msft_opcode);
+		else
+			virtio_cread(vdev, struct virtio_bt_config,
+				     msft_opcode, &msft_opcode);
+
+		hci_set_msft_opcode(hdev, msft_opcode);
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_AOSP_EXT))
+		hci_set_aosp_capable(hdev);
+
+	if (hci_register_dev(hdev) < 0) {
+		hci_free_dev(hdev);
+		err = -EBUSY;
+		goto failed;
+	}
+
+	virtio_device_ready(vdev);
+	err = virtbt_open_vdev(vbt);
+	if (err)
+		goto open_failed;
+
+	return 0;
+
+open_failed:
+	hci_free_dev(hdev);
+failed:
+	vdev->config->del_vqs(vdev);
+	return err;
+}
+
+static void virtbt_remove(struct virtio_device *vdev)
+{
+	struct virtio_bluetooth *vbt = vdev->priv;
+	struct hci_dev *hdev = vbt->hdev;
+
+	hci_unregister_dev(hdev);
+	virtio_reset_device(vdev);
+	virtbt_close_vdev(vbt);
+
+	hci_free_dev(hdev);
+	vbt->hdev = NULL;
+
+	vdev->config->del_vqs(vdev);
+	kfree(vbt);
+}
+
+static struct virtio_device_id virtbt_table[] = {
+	{ VIRTIO_ID_BT, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+MODULE_DEVICE_TABLE(virtio, virtbt_table);
+
+static const unsigned int virtbt_features[] = {
+	VIRTIO_BT_F_VND_HCI,
+	VIRTIO_BT_F_MSFT_EXT,
+	VIRTIO_BT_F_AOSP_EXT,
+	VIRTIO_BT_F_CONFIG_V2,
+};
+
+static struct virtio_driver virtbt_driver = {
+	.driver.name         = KBUILD_MODNAME,
+	.feature_table       = virtbt_features,
+	.feature_table_size  = ARRAY_SIZE(virtbt_features),
+	.id_table            = virtbt_table,
+	.probe               = virtbt_probe,
+	.remove              = virtbt_remove,
+};
+
+module_virtio_driver(virtbt_driver);
+
+MODULE_AUTHOR("Marcel Holtmann <marcel@holtmann.org>");
+MODULE_DESCRIPTION("Generic Bluetooth VIRTIO driver ver " VERSION);
+MODULE_VERSION(VERSION);
+MODULE_LICENSE("GPL");