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, 59 insertions, 0 deletions

diff --git a/drivers/net/wireguard/cookie.h b/drivers/net/wireguard/cookie.h
new file mode 100644
index 000000000..c4bd61ca0
--- /dev/null
+++ b/drivers/net/wireguard/cookie.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#ifndef _WG_COOKIE_H
+#define _WG_COOKIE_H
+
+#include "messages.h"
+#include <linux/rwsem.h>
+
+struct wg_peer;
+
+struct cookie_checker {
+	u8 secret[NOISE_HASH_LEN];
+	u8 cookie_encryption_key[NOISE_SYMMETRIC_KEY_LEN];
+	u8 message_mac1_key[NOISE_SYMMETRIC_KEY_LEN];
+	u64 secret_birthdate;
+	struct rw_semaphore secret_lock;
+	struct wg_device *device;
+};
+
+struct cookie {
+	u64 birthdate;
+	bool is_valid;
+	u8 cookie[COOKIE_LEN];
+	bool have_sent_mac1;
+	u8 last_mac1_sent[COOKIE_LEN];
+	u8 cookie_decryption_key[NOISE_SYMMETRIC_KEY_LEN];
+	u8 message_mac1_key[NOISE_SYMMETRIC_KEY_LEN];
+	struct rw_semaphore lock;
+};
+
+enum cookie_mac_state {
+	INVALID_MAC,
+	VALID_MAC_BUT_NO_COOKIE,
+	VALID_MAC_WITH_COOKIE_BUT_RATELIMITED,
+	VALID_MAC_WITH_COOKIE
+};
+
+void wg_cookie_checker_init(struct cookie_checker *checker,
+			    struct wg_device *wg);
+void wg_cookie_checker_precompute_device_keys(struct cookie_checker *checker);
+void wg_cookie_checker_precompute_peer_keys(struct wg_peer *peer);
+void wg_cookie_init(struct cookie *cookie);
+
+enum cookie_mac_state wg_cookie_validate_packet(struct cookie_checker *checker,
+						struct sk_buff *skb,
+						bool check_cookie);
+void wg_cookie_add_mac_to_packet(void *message, size_t len,
+				 struct wg_peer *peer);
+
+void wg_cookie_message_create(struct message_handshake_cookie *src,
+			      struct sk_buff *skb, __le32 index,
+			      struct cookie_checker *checker);
+void wg_cookie_message_consume(struct message_handshake_cookie *src,
+			       struct wg_device *wg);
+
+#endif /* _WG_COOKIE_H */