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, 187 insertions, 0 deletions

diff --git a/crypto/cbc.c b/crypto/cbc.c
new file mode 100644
index 000000000..ed3df6246
--- /dev/null
+++ b/crypto/cbc.c
@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * CBC: Cipher Block Chaining mode
+ *
+ * Copyright (c) 2006-2016 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+
+#include <crypto/internal/skcipher.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/log2.h>
+#include <linux/module.h>
+
+static int crypto_cbc_encrypt_segment(struct crypto_lskcipher *tfm,
+				      const u8 *src, u8 *dst, unsigned nbytes,
+				      u8 *iv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+
+	for (; nbytes >= bsize; src += bsize, dst += bsize, nbytes -= bsize) {
+		crypto_xor(iv, src, bsize);
+		crypto_lskcipher_encrypt(tfm, iv, dst, bsize, NULL);
+		memcpy(iv, dst, bsize);
+	}
+
+	return nbytes;
+}
+
+static int crypto_cbc_encrypt_inplace(struct crypto_lskcipher *tfm,
+				      u8 *src, unsigned nbytes, u8 *oiv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	u8 *iv = oiv;
+
+	if (nbytes < bsize)
+		goto out;
+
+	do {
+		crypto_xor(src, iv, bsize);
+		crypto_lskcipher_encrypt(tfm, src, src, bsize, NULL);
+		iv = src;
+
+		src += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(oiv, iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_encrypt(struct crypto_lskcipher *tfm, const u8 *src,
+			      u8 *dst, unsigned len, u8 *iv, u32 flags)
+{
+	struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
+	bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
+	struct crypto_lskcipher *cipher = *ctx;
+	int rem;
+
+	if (src == dst)
+		rem = crypto_cbc_encrypt_inplace(cipher, dst, len, iv);
+	else
+		rem = crypto_cbc_encrypt_segment(cipher, src, dst, len, iv);
+
+	return rem && final ? -EINVAL : rem;
+}
+
+static int crypto_cbc_decrypt_segment(struct crypto_lskcipher *tfm,
+				      const u8 *src, u8 *dst, unsigned nbytes,
+				      u8 *oiv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	const u8 *iv = oiv;
+
+	if (nbytes < bsize)
+		goto out;
+
+	do {
+		crypto_lskcipher_decrypt(tfm, src, dst, bsize, NULL);
+		crypto_xor(dst, iv, bsize);
+		iv = src;
+
+		src += bsize;
+		dst += bsize;
+	} while ((nbytes -= bsize) >= bsize);
+
+	memcpy(oiv, iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_decrypt_inplace(struct crypto_lskcipher *tfm,
+				      u8 *src, unsigned nbytes, u8 *iv)
+{
+	unsigned int bsize = crypto_lskcipher_blocksize(tfm);
+	u8 last_iv[MAX_CIPHER_BLOCKSIZE];
+
+	if (nbytes < bsize)
+		goto out;
+
+	/* Start of the last block. */
+	src += nbytes - (nbytes & (bsize - 1)) - bsize;
+	memcpy(last_iv, src, bsize);
+
+	for (;;) {
+		crypto_lskcipher_decrypt(tfm, src, src, bsize, NULL);
+		if ((nbytes -= bsize) < bsize)
+			break;
+		crypto_xor(src, src - bsize, bsize);
+		src -= bsize;
+	}
+
+	crypto_xor(src, iv, bsize);
+	memcpy(iv, last_iv, bsize);
+
+out:
+	return nbytes;
+}
+
+static int crypto_cbc_decrypt(struct crypto_lskcipher *tfm, const u8 *src,
+			      u8 *dst, unsigned len, u8 *iv, u32 flags)
+{
+	struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
+	bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
+	struct crypto_lskcipher *cipher = *ctx;
+	int rem;
+
+	if (src == dst)
+		rem = crypto_cbc_decrypt_inplace(cipher, dst, len, iv);
+	else
+		rem = crypto_cbc_decrypt_segment(cipher, src, dst, len, iv);
+
+	return rem && final ? -EINVAL : rem;
+}
+
+static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	struct lskcipher_instance *inst;
+	int err;
+
+	inst = lskcipher_alloc_instance_simple(tmpl, tb);
+	if (IS_ERR(inst))
+		return PTR_ERR(inst);
+
+	err = -EINVAL;
+	if (!is_power_of_2(inst->alg.co.base.cra_blocksize))
+		goto out_free_inst;
+
+	if (inst->alg.co.statesize)
+		goto out_free_inst;
+
+	inst->alg.encrypt = crypto_cbc_encrypt;
+	inst->alg.decrypt = crypto_cbc_decrypt;
+
+	err = lskcipher_register_instance(tmpl, inst);
+	if (err) {
+out_free_inst:
+		inst->free(inst);
+	}
+
+	return err;
+}
+
+static struct crypto_template crypto_cbc_tmpl = {
+	.name = "cbc",
+	.create = crypto_cbc_create,
+	.module = THIS_MODULE,
+};
+
+static int __init crypto_cbc_module_init(void)
+{
+	return crypto_register_template(&crypto_cbc_tmpl);
+}
+
+static void __exit crypto_cbc_module_exit(void)
+{
+	crypto_unregister_template(&crypto_cbc_tmpl);
+}
+
+module_init(crypto_cbc_module_init);
+module_exit(crypto_cbc_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CBC block cipher mode of operation");
+MODULE_ALIAS_CRYPTO("cbc");