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, 344 insertions, 0 deletions

diff --git a/net/nfc/hci/command.c b/net/nfc/hci/command.c
new file mode 100644
index 000000000..af6bacb3b
--- /dev/null
+++ b/net/nfc/hci/command.c
@@ -0,0 +1,344 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2012  Intel Corporation. All rights reserved.
+ */
+
+#define pr_fmt(fmt) "hci: %s: " fmt, __func__
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+
+#include <net/nfc/hci.h>
+
+#include "hci.h"
+
+#define MAX_FWI 4949
+
+static int nfc_hci_execute_cmd_async(struct nfc_hci_dev *hdev, u8 pipe, u8 cmd,
+			       const u8 *param, size_t param_len,
+			       data_exchange_cb_t cb, void *cb_context)
+{
+	pr_debug("exec cmd async through pipe=%d, cmd=%d, plen=%zd\n", pipe,
+		 cmd, param_len);
+
+	/* TODO: Define hci cmd execution delay. Should it be the same
+	 * for all commands?
+	 */
+	return nfc_hci_hcp_message_tx(hdev, pipe, NFC_HCI_HCP_COMMAND, cmd,
+				      param, param_len, cb, cb_context, MAX_FWI);
+}
+
+/*
+ * HCI command execution completion callback.
+ * err will be a standard linux error (may be converted from HCI response)
+ * skb contains the response data and must be disposed, or may be NULL if
+ * an error occurred
+ */
+static void nfc_hci_execute_cb(void *context, struct sk_buff *skb, int err)
+{
+	struct hcp_exec_waiter *hcp_ew = (struct hcp_exec_waiter *)context;
+
+	pr_debug("HCI Cmd completed with result=%d\n", err);
+
+	hcp_ew->exec_result = err;
+	if (hcp_ew->exec_result == 0)
+		hcp_ew->result_skb = skb;
+	else
+		kfree_skb(skb);
+	hcp_ew->exec_complete = true;
+
+	wake_up(hcp_ew->wq);
+}
+
+static int nfc_hci_execute_cmd(struct nfc_hci_dev *hdev, u8 pipe, u8 cmd,
+			       const u8 *param, size_t param_len,
+			       struct sk_buff **skb)
+{
+	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(ew_wq);
+	struct hcp_exec_waiter hcp_ew;
+	hcp_ew.wq = &ew_wq;
+	hcp_ew.exec_complete = false;
+	hcp_ew.result_skb = NULL;
+
+	pr_debug("exec cmd sync through pipe=%d, cmd=%d, plen=%zd\n", pipe,
+		 cmd, param_len);
+
+	/* TODO: Define hci cmd execution delay. Should it be the same
+	 * for all commands?
+	 */
+	hcp_ew.exec_result = nfc_hci_hcp_message_tx(hdev, pipe,
+						    NFC_HCI_HCP_COMMAND, cmd,
+						    param, param_len,
+						    nfc_hci_execute_cb, &hcp_ew,
+						    MAX_FWI);
+	if (hcp_ew.exec_result < 0)
+		return hcp_ew.exec_result;
+
+	wait_event(ew_wq, hcp_ew.exec_complete == true);
+
+	if (hcp_ew.exec_result == 0) {
+		if (skb)
+			*skb = hcp_ew.result_skb;
+		else
+			kfree_skb(hcp_ew.result_skb);
+	}
+
+	return hcp_ew.exec_result;
+}
+
+int nfc_hci_send_event(struct nfc_hci_dev *hdev, u8 gate, u8 event,
+		       const u8 *param, size_t param_len)
+{
+	u8 pipe;
+
+	pr_debug("%d to gate %d\n", event, gate);
+
+	pipe = hdev->gate2pipe[gate];
+	if (pipe == NFC_HCI_INVALID_PIPE)
+		return -EADDRNOTAVAIL;
+
+	return nfc_hci_hcp_message_tx(hdev, pipe, NFC_HCI_HCP_EVENT, event,
+				      param, param_len, NULL, NULL, 0);
+}
+EXPORT_SYMBOL(nfc_hci_send_event);
+
+/*
+ * Execute an hci command sent to gate.
+ * skb will contain response data if success. skb can be NULL if you are not
+ * interested by the response.
+ */
+int nfc_hci_send_cmd(struct nfc_hci_dev *hdev, u8 gate, u8 cmd,
+		     const u8 *param, size_t param_len, struct sk_buff **skb)
+{
+	u8 pipe;
+
+	pipe = hdev->gate2pipe[gate];
+	if (pipe == NFC_HCI_INVALID_PIPE)
+		return -EADDRNOTAVAIL;
+
+	return nfc_hci_execute_cmd(hdev, pipe, cmd, param, param_len, skb);
+}
+EXPORT_SYMBOL(nfc_hci_send_cmd);
+
+int nfc_hci_send_cmd_async(struct nfc_hci_dev *hdev, u8 gate, u8 cmd,
+			   const u8 *param, size_t param_len,
+			   data_exchange_cb_t cb, void *cb_context)
+{
+	u8 pipe;
+
+	pipe = hdev->gate2pipe[gate];
+	if (pipe == NFC_HCI_INVALID_PIPE)
+		return -EADDRNOTAVAIL;
+
+	return nfc_hci_execute_cmd_async(hdev, pipe, cmd, param, param_len,
+					 cb, cb_context);
+}
+EXPORT_SYMBOL(nfc_hci_send_cmd_async);
+
+int nfc_hci_set_param(struct nfc_hci_dev *hdev, u8 gate, u8 idx,
+		      const u8 *param, size_t param_len)
+{
+	int r;
+	u8 *tmp;
+
+	/* TODO ELa: reg idx must be inserted before param, but we don't want
+	 * to ask the caller to do it to keep a simpler API.
+	 * For now, just create a new temporary param buffer. This is far from
+	 * optimal though, and the plan is to modify APIs to pass idx down to
+	 * nfc_hci_hcp_message_tx where the frame is actually built, thereby
+	 * eliminating the need for the temp allocation-copy here.
+	 */
+
+	pr_debug("idx=%d to gate %d\n", idx, gate);
+
+	tmp = kmalloc(1 + param_len, GFP_KERNEL);
+	if (tmp == NULL)
+		return -ENOMEM;
+
+	*tmp = idx;
+	memcpy(tmp + 1, param, param_len);
+
+	r = nfc_hci_send_cmd(hdev, gate, NFC_HCI_ANY_SET_PARAMETER,
+			     tmp, param_len + 1, NULL);
+
+	kfree(tmp);
+
+	return r;
+}
+EXPORT_SYMBOL(nfc_hci_set_param);
+
+int nfc_hci_get_param(struct nfc_hci_dev *hdev, u8 gate, u8 idx,
+		      struct sk_buff **skb)
+{
+	pr_debug("gate=%d regidx=%d\n", gate, idx);
+
+	return nfc_hci_send_cmd(hdev, gate, NFC_HCI_ANY_GET_PARAMETER,
+				&idx, 1, skb);
+}
+EXPORT_SYMBOL(nfc_hci_get_param);
+
+static int nfc_hci_open_pipe(struct nfc_hci_dev *hdev, u8 pipe)
+{
+	struct sk_buff *skb;
+	int r;
+
+	pr_debug("pipe=%d\n", pipe);
+
+	r = nfc_hci_execute_cmd(hdev, pipe, NFC_HCI_ANY_OPEN_PIPE,
+				NULL, 0, &skb);
+	if (r == 0) {
+		/* dest host other than host controller will send
+		 * number of pipes already open on this gate before
+		 * execution. The number can be found in skb->data[0]
+		 */
+		kfree_skb(skb);
+	}
+
+	return r;
+}
+
+static int nfc_hci_close_pipe(struct nfc_hci_dev *hdev, u8 pipe)
+{
+	return nfc_hci_execute_cmd(hdev, pipe, NFC_HCI_ANY_CLOSE_PIPE,
+				   NULL, 0, NULL);
+}
+
+static u8 nfc_hci_create_pipe(struct nfc_hci_dev *hdev, u8 dest_host,
+			      u8 dest_gate, int *result)
+{
+	struct sk_buff *skb;
+	struct hci_create_pipe_params params;
+	struct hci_create_pipe_resp *resp;
+	u8 pipe;
+
+	pr_debug("gate=%d\n", dest_gate);
+
+	params.src_gate = NFC_HCI_ADMIN_GATE;
+	params.dest_host = dest_host;
+	params.dest_gate = dest_gate;
+
+	*result = nfc_hci_execute_cmd(hdev, NFC_HCI_ADMIN_PIPE,
+				      NFC_HCI_ADM_CREATE_PIPE,
+				      (u8 *) &params, sizeof(params), &skb);
+	if (*result < 0)
+		return NFC_HCI_INVALID_PIPE;
+
+	resp = (struct hci_create_pipe_resp *)skb->data;
+	pipe = resp->pipe;
+	kfree_skb(skb);
+
+	pr_debug("pipe created=%d\n", pipe);
+
+	return pipe;
+}
+
+static int nfc_hci_delete_pipe(struct nfc_hci_dev *hdev, u8 pipe)
+{
+	return nfc_hci_execute_cmd(hdev, NFC_HCI_ADMIN_PIPE,
+				   NFC_HCI_ADM_DELETE_PIPE, &pipe, 1, NULL);
+}
+
+static int nfc_hci_clear_all_pipes(struct nfc_hci_dev *hdev)
+{
+	u8 param[2];
+	size_t param_len = 2;
+
+	/* TODO: Find out what the identity reference data is
+	 * and fill param with it. HCI spec 6.1.3.5 */
+
+	if (test_bit(NFC_HCI_QUIRK_SHORT_CLEAR, &hdev->quirks))
+		param_len = 0;
+
+	return nfc_hci_execute_cmd(hdev, NFC_HCI_ADMIN_PIPE,
+				   NFC_HCI_ADM_CLEAR_ALL_PIPE, param, param_len,
+				   NULL);
+}
+
+int nfc_hci_disconnect_gate(struct nfc_hci_dev *hdev, u8 gate)
+{
+	int r;
+	u8 pipe = hdev->gate2pipe[gate];
+
+	if (pipe == NFC_HCI_INVALID_PIPE)
+		return -EADDRNOTAVAIL;
+
+	r = nfc_hci_close_pipe(hdev, pipe);
+	if (r < 0)
+		return r;
+
+	if (pipe != NFC_HCI_LINK_MGMT_PIPE && pipe != NFC_HCI_ADMIN_PIPE) {
+		r = nfc_hci_delete_pipe(hdev, pipe);
+		if (r < 0)
+			return r;
+	}
+
+	hdev->gate2pipe[gate] = NFC_HCI_INVALID_PIPE;
+
+	return 0;
+}
+EXPORT_SYMBOL(nfc_hci_disconnect_gate);
+
+int nfc_hci_disconnect_all_gates(struct nfc_hci_dev *hdev)
+{
+	int r;
+
+	r = nfc_hci_clear_all_pipes(hdev);
+	if (r < 0)
+		return r;
+
+	nfc_hci_reset_pipes(hdev);
+
+	return 0;
+}
+EXPORT_SYMBOL(nfc_hci_disconnect_all_gates);
+
+int nfc_hci_connect_gate(struct nfc_hci_dev *hdev, u8 dest_host, u8 dest_gate,
+			 u8 pipe)
+{
+	bool pipe_created = false;
+	int r;
+
+	if (pipe == NFC_HCI_DO_NOT_CREATE_PIPE)
+		return 0;
+
+	if (hdev->gate2pipe[dest_gate] != NFC_HCI_INVALID_PIPE)
+		return -EADDRINUSE;
+
+	if (pipe != NFC_HCI_INVALID_PIPE)
+		goto open_pipe;
+
+	switch (dest_gate) {
+	case NFC_HCI_LINK_MGMT_GATE:
+		pipe = NFC_HCI_LINK_MGMT_PIPE;
+		break;
+	case NFC_HCI_ADMIN_GATE:
+		pipe = NFC_HCI_ADMIN_PIPE;
+		break;
+	default:
+		pipe = nfc_hci_create_pipe(hdev, dest_host, dest_gate, &r);
+		if (pipe == NFC_HCI_INVALID_PIPE)
+			return r;
+		pipe_created = true;
+		break;
+	}
+
+open_pipe:
+	r = nfc_hci_open_pipe(hdev, pipe);
+	if (r < 0) {
+		if (pipe_created)
+			if (nfc_hci_delete_pipe(hdev, pipe) < 0) {
+				/* TODO: Cannot clean by deleting pipe...
+				 * -> inconsistent state */
+			}
+		return r;
+	}
+
+	hdev->pipes[pipe].gate = dest_gate;
+	hdev->pipes[pipe].dest_host = dest_host;
+	hdev->gate2pipe[dest_gate] = pipe;
+
+	return 0;
+}
+EXPORT_SYMBOL(nfc_hci_connect_gate);