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, 201 insertions, 0 deletions

diff --git a/crypto/mldsa.c b/crypto/mldsa.c
new file mode 100644
index 000000000..d8de082cc
--- /dev/null
+++ b/crypto/mldsa.c
@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * crypto_sig wrapper around ML-DSA library.
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <crypto/internal/sig.h>
+#include <crypto/mldsa.h>
+
+struct crypto_mldsa_ctx {
+	u8 pk[MAX(MAX(MLDSA44_PUBLIC_KEY_SIZE,
+		      MLDSA65_PUBLIC_KEY_SIZE),
+		  MLDSA87_PUBLIC_KEY_SIZE)];
+	unsigned int pk_len;
+	enum mldsa_alg strength;
+	bool key_set;
+};
+
+static int crypto_mldsa_sign(struct crypto_sig *tfm,
+			     const void *msg, unsigned int msg_len,
+			     void *sig, unsigned int sig_len)
+{
+	return -EOPNOTSUPP;
+}
+
+static int crypto_mldsa_verify(struct crypto_sig *tfm,
+			       const void *sig, unsigned int sig_len,
+			       const void *msg, unsigned int msg_len)
+{
+	const struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	if (unlikely(!ctx->key_set))
+		return -EINVAL;
+
+	return mldsa_verify(ctx->strength, sig, sig_len, msg, msg_len,
+			    ctx->pk, ctx->pk_len);
+}
+
+static unsigned int crypto_mldsa_key_size(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	switch (ctx->strength) {
+	case MLDSA44:
+		return MLDSA44_PUBLIC_KEY_SIZE;
+	case MLDSA65:
+		return MLDSA65_PUBLIC_KEY_SIZE;
+	case MLDSA87:
+		return MLDSA87_PUBLIC_KEY_SIZE;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+static int crypto_mldsa_set_pub_key(struct crypto_sig *tfm,
+				    const void *key, unsigned int keylen)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+	unsigned int expected_len = crypto_mldsa_key_size(tfm);
+
+	if (keylen != expected_len)
+		return -EINVAL;
+
+	ctx->pk_len = keylen;
+	memcpy(ctx->pk, key, keylen);
+	ctx->key_set = true;
+	return 0;
+}
+
+static int crypto_mldsa_set_priv_key(struct crypto_sig *tfm,
+				     const void *key, unsigned int keylen)
+{
+	return -EOPNOTSUPP;
+}
+
+static unsigned int crypto_mldsa_max_size(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	switch (ctx->strength) {
+	case MLDSA44:
+		return MLDSA44_SIGNATURE_SIZE;
+	case MLDSA65:
+		return MLDSA65_SIGNATURE_SIZE;
+	case MLDSA87:
+		return MLDSA87_SIGNATURE_SIZE;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+static int crypto_mldsa44_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA44;
+	ctx->key_set = false;
+	return 0;
+}
+
+static int crypto_mldsa65_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA65;
+	ctx->key_set = false;
+	return 0;
+}
+
+static int crypto_mldsa87_alg_init(struct crypto_sig *tfm)
+{
+	struct crypto_mldsa_ctx *ctx = crypto_sig_ctx(tfm);
+
+	ctx->strength = MLDSA87;
+	ctx->key_set = false;
+	return 0;
+}
+
+static void crypto_mldsa_alg_exit(struct crypto_sig *tfm)
+{
+}
+
+static struct sig_alg crypto_mldsa_algs[] = {
+	{
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa44_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa44",
+		.base.cra_driver_name	= "mldsa44-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	}, {
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa65_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa65",
+		.base.cra_driver_name	= "mldsa65-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	}, {
+		.sign			= crypto_mldsa_sign,
+		.verify			= crypto_mldsa_verify,
+		.set_pub_key		= crypto_mldsa_set_pub_key,
+		.set_priv_key		= crypto_mldsa_set_priv_key,
+		.key_size		= crypto_mldsa_key_size,
+		.max_size		= crypto_mldsa_max_size,
+		.init			= crypto_mldsa87_alg_init,
+		.exit			= crypto_mldsa_alg_exit,
+		.base.cra_name		= "mldsa87",
+		.base.cra_driver_name	= "mldsa87-lib",
+		.base.cra_ctxsize	= sizeof(struct crypto_mldsa_ctx),
+		.base.cra_module	= THIS_MODULE,
+		.base.cra_priority	= 5000,
+	},
+};
+
+static int __init mldsa_init(void)
+{
+	int ret, i;
+
+	for (i = 0; i < ARRAY_SIZE(crypto_mldsa_algs); i++) {
+		ret = crypto_register_sig(&crypto_mldsa_algs[i]);
+		if (ret < 0)
+			goto error;
+	}
+	return 0;
+
+error:
+	pr_err("Failed to register (%d)\n", ret);
+	for (i--; i >= 0; i--)
+		crypto_unregister_sig(&crypto_mldsa_algs[i]);
+	return ret;
+}
+module_init(mldsa_init);
+
+static void mldsa_exit(void)
+{
+	for (int i = 0; i < ARRAY_SIZE(crypto_mldsa_algs); i++)
+		crypto_unregister_sig(&crypto_mldsa_algs[i]);
+}
+module_exit(mldsa_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Crypto API support for ML-DSA signature verification");
+MODULE_ALIAS_CRYPTO("mldsa44");
+MODULE_ALIAS_CRYPTO("mldsa65");
+MODULE_ALIAS_CRYPTO("mldsa87");