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, 171 insertions, 0 deletions

diff --git a/net/nfc/digital.h b/net/nfc/digital.h
new file mode 100644
index 000000000..c33b2f7e1
--- /dev/null
+++ b/net/nfc/digital.h
@@ -0,0 +1,171 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * NFC Digital Protocol stack
+ * Copyright (c) 2013, Intel Corporation.
+ */
+
+#ifndef __DIGITAL_H
+#define __DIGITAL_H
+
+#include <net/nfc/nfc.h>
+#include <net/nfc/digital.h>
+
+#include <linux/crc-ccitt.h>
+#include <linux/crc-itu-t.h>
+
+#define PROTOCOL_ERR(req) pr_err("%d: NFC Digital Protocol error: %s\n", \
+				 __LINE__, req)
+
+#define DIGITAL_CMD_IN_SEND        0
+#define DIGITAL_CMD_TG_SEND        1
+#define DIGITAL_CMD_TG_LISTEN      2
+#define DIGITAL_CMD_TG_LISTEN_MDAA 3
+#define DIGITAL_CMD_TG_LISTEN_MD   4
+
+#define DIGITAL_MAX_HEADER_LEN 7
+#define DIGITAL_CRC_LEN        2
+
+#define DIGITAL_SENSF_NFCID2_NFC_DEP_B1 0x01
+#define DIGITAL_SENSF_NFCID2_NFC_DEP_B2 0xFE
+
+#define DIGITAL_SENS_RES_NFC_DEP 0x0100
+#define DIGITAL_SEL_RES_NFC_DEP  0x40
+#define DIGITAL_SENSF_FELICA_SC  0xFFFF
+
+#define DIGITAL_DRV_CAPS_IN_CRC(ddev) \
+	((ddev)->driver_capabilities & NFC_DIGITAL_DRV_CAPS_IN_CRC)
+#define DIGITAL_DRV_CAPS_TG_CRC(ddev) \
+	((ddev)->driver_capabilities & NFC_DIGITAL_DRV_CAPS_TG_CRC)
+
+struct digital_data_exch {
+	data_exchange_cb_t cb;
+	void *cb_context;
+};
+
+struct sk_buff *digital_skb_alloc(struct nfc_digital_dev *ddev,
+				  unsigned int len);
+
+int digital_send_cmd(struct nfc_digital_dev *ddev, u8 cmd_type,
+		     struct sk_buff *skb, struct digital_tg_mdaa_params *params,
+		     u16 timeout, nfc_digital_cmd_complete_t cmd_cb,
+		     void *cb_context);
+
+int digital_in_configure_hw(struct nfc_digital_dev *ddev, int type, int param);
+static inline int digital_in_send_cmd(struct nfc_digital_dev *ddev,
+				      struct sk_buff *skb, u16 timeout,
+				      nfc_digital_cmd_complete_t cmd_cb,
+				      void *cb_context)
+{
+	return digital_send_cmd(ddev, DIGITAL_CMD_IN_SEND, skb, NULL, timeout,
+				cmd_cb, cb_context);
+}
+
+void digital_poll_next_tech(struct nfc_digital_dev *ddev);
+
+int digital_in_send_sens_req(struct nfc_digital_dev *ddev, u8 rf_tech);
+int digital_in_send_sensb_req(struct nfc_digital_dev *ddev, u8 rf_tech);
+int digital_in_send_sensf_req(struct nfc_digital_dev *ddev, u8 rf_tech);
+int digital_in_send_iso15693_inv_req(struct nfc_digital_dev *ddev, u8 rf_tech);
+
+int digital_in_iso_dep_pull_sod(struct nfc_digital_dev *ddev,
+				struct sk_buff *skb);
+int digital_in_iso_dep_push_sod(struct nfc_digital_dev *ddev,
+				struct sk_buff *skb);
+
+int digital_target_found(struct nfc_digital_dev *ddev,
+			 struct nfc_target *target, u8 protocol);
+
+int digital_in_recv_mifare_res(struct sk_buff *resp);
+
+int digital_in_send_atr_req(struct nfc_digital_dev *ddev,
+			    struct nfc_target *target, __u8 comm_mode, __u8 *gb,
+			    size_t gb_len);
+int digital_in_send_dep_req(struct nfc_digital_dev *ddev,
+			    struct nfc_target *target, struct sk_buff *skb,
+			    struct digital_data_exch *data_exch);
+
+int digital_tg_configure_hw(struct nfc_digital_dev *ddev, int type, int param);
+static inline int digital_tg_send_cmd(struct nfc_digital_dev *ddev,
+			struct sk_buff *skb, u16 timeout,
+			nfc_digital_cmd_complete_t cmd_cb, void *cb_context)
+{
+	return digital_send_cmd(ddev, DIGITAL_CMD_TG_SEND, skb, NULL, timeout,
+				cmd_cb, cb_context);
+}
+
+void digital_tg_recv_sens_req(struct nfc_digital_dev *ddev, void *arg,
+			      struct sk_buff *resp);
+
+void digital_tg_recv_sensf_req(struct nfc_digital_dev *ddev, void *arg,
+			       struct sk_buff *resp);
+
+static inline int digital_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
+				    nfc_digital_cmd_complete_t cb, void *arg)
+{
+	return digital_send_cmd(ddev, DIGITAL_CMD_TG_LISTEN, NULL, NULL,
+				timeout, cb, arg);
+}
+
+void digital_tg_recv_atr_req(struct nfc_digital_dev *ddev, void *arg,
+			     struct sk_buff *resp);
+
+int digital_tg_send_dep_res(struct nfc_digital_dev *ddev, struct sk_buff *skb);
+
+int digital_tg_listen_nfca(struct nfc_digital_dev *ddev, u8 rf_tech);
+int digital_tg_listen_nfcf(struct nfc_digital_dev *ddev, u8 rf_tech);
+void digital_tg_recv_md_req(struct nfc_digital_dev *ddev, void *arg,
+			    struct sk_buff *resp);
+
+typedef u16 (*crc_func_t)(u16, const u8 *, size_t);
+
+#define CRC_A_INIT 0x6363
+#define CRC_B_INIT 0xFFFF
+#define CRC_F_INIT 0x0000
+
+void digital_skb_add_crc(struct sk_buff *skb, crc_func_t crc_func, u16 init,
+			 u8 bitwise_inv, u8 msb_first);
+
+static inline void digital_skb_add_crc_a(struct sk_buff *skb)
+{
+	digital_skb_add_crc(skb, crc_ccitt, CRC_A_INIT, 0, 0);
+}
+
+static inline void digital_skb_add_crc_b(struct sk_buff *skb)
+{
+	digital_skb_add_crc(skb, crc_ccitt, CRC_B_INIT, 1, 0);
+}
+
+static inline void digital_skb_add_crc_f(struct sk_buff *skb)
+{
+	digital_skb_add_crc(skb, crc_itu_t, CRC_F_INIT, 0, 1);
+}
+
+static inline void digital_skb_add_crc_none(struct sk_buff *skb)
+{
+	return;
+}
+
+int digital_skb_check_crc(struct sk_buff *skb, crc_func_t crc_func,
+			  u16 crc_init, u8 bitwise_inv, u8 msb_first);
+
+static inline int digital_skb_check_crc_a(struct sk_buff *skb)
+{
+	return digital_skb_check_crc(skb, crc_ccitt, CRC_A_INIT, 0, 0);
+}
+
+static inline int digital_skb_check_crc_b(struct sk_buff *skb)
+{
+	return digital_skb_check_crc(skb, crc_ccitt, CRC_B_INIT, 1, 0);
+}
+
+static inline int digital_skb_check_crc_f(struct sk_buff *skb)
+{
+	return digital_skb_check_crc(skb, crc_itu_t, CRC_F_INIT, 0, 1);
+}
+
+static inline int digital_skb_check_crc_none(struct sk_buff *skb)
+{
+	return 0;
+}
+
+#endif /* __DIGITAL_H */