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, 52 insertions, 0 deletions

diff --git a/net/mptcp/crypto.c b/net/mptcp/crypto.c
new file mode 100644
index 000000000..31948e18d
--- /dev/null
+++ b/net/mptcp/crypto.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP cryptographic functions
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ *
+ * Note: This code is based on mptcp_ctrl.c, mptcp_ipv4.c, and
+ *       mptcp_ipv6 from multipath-tcp.org, authored by:
+ *
+ *       Sébastien Barré <sebastien.barre@uclouvain.be>
+ *       Christoph Paasch <christoph.paasch@uclouvain.be>
+ *       Jaakko Korkeaniemi <jaakko.korkeaniemi@aalto.fi>
+ *       Gregory Detal <gregory.detal@uclouvain.be>
+ *       Fabien Duchêne <fabien.duchene@uclouvain.be>
+ *       Andreas Seelinger <Andreas.Seelinger@rwth-aachen.de>
+ *       Lavkesh Lahngir <lavkesh51@gmail.com>
+ *       Andreas Ripke <ripke@neclab.eu>
+ *       Vlad Dogaru <vlad.dogaru@intel.com>
+ *       Octavian Purdila <octavian.purdila@intel.com>
+ *       John Ronan <jronan@tssg.org>
+ *       Catalin Nicutar <catalin.nicutar@gmail.com>
+ *       Brandon Heller <brandonh@stanford.edu>
+ */
+
+#include <linux/kernel.h>
+#include <crypto/sha2.h>
+
+#include "protocol.h"
+
+#define SHA256_DIGEST_WORDS (SHA256_DIGEST_SIZE / 4)
+
+void mptcp_crypto_key_sha(u64 key, u32 *token, u64 *idsn)
+{
+	__be32 mptcp_hashed_key[SHA256_DIGEST_WORDS];
+	__be64 input = cpu_to_be64(key);
+
+	sha256((__force u8 *)&input, sizeof(input), (u8 *)mptcp_hashed_key);
+
+	if (token)
+		*token = be32_to_cpu(mptcp_hashed_key[0]);
+	if (idsn)
+		*idsn = be64_to_cpu(*((__be64 *)&mptcp_hashed_key[6]));
+}
+
+void mptcp_crypto_hmac_sha(u64 key1, u64 key2, u8 *msg, int len, void *hmac)
+{
+	__be64 key[2] = { cpu_to_be64(key1), cpu_to_be64(key2) };
+
+	hmac_sha256_usingrawkey((const u8 *)key, sizeof(key), msg, len, hmac);
+}
+
+#if IS_MODULE(CONFIG_MPTCP_KUNIT_TEST)
+EXPORT_SYMBOL_GPL(mptcp_crypto_hmac_sha);
+#endif