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, 53 insertions, 0 deletions

diff --git a/net/ceph/crypto.h b/net/ceph/crypto.h
new file mode 100644
index 000000000..3a2ade15a
--- /dev/null
+++ b/net/ceph/crypto.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _FS_CEPH_CRYPTO_H
+#define _FS_CEPH_CRYPTO_H
+
+#include <crypto/sha2.h>
+#include <linux/ceph/types.h>
+#include <linux/ceph/buffer.h>
+
+#define CEPH_MAX_KEY_LEN		32
+#define CEPH_MAX_CON_SECRET_LEN		64
+
+/*
+ * cryptographic secret
+ */
+struct ceph_crypto_key {
+	int type;
+	struct ceph_timespec created;
+	int len;
+	void *key;
+
+	union {
+		struct crypto_sync_skcipher *aes_tfm;
+		struct {
+			struct hmac_sha256_key hmac_key;
+			const struct krb5_enctype *krb5_type;
+			struct crypto_aead *krb5_tfms[3];
+		};
+	};
+};
+
+int ceph_crypto_key_prepare(struct ceph_crypto_key *key,
+			    const u32 *key_usages, int key_usage_cnt);
+int ceph_crypto_key_clone(struct ceph_crypto_key *dst,
+			  const struct ceph_crypto_key *src);
+int ceph_crypto_key_decode(struct ceph_crypto_key *key, void **p, void *end);
+int ceph_crypto_key_unarmor(struct ceph_crypto_key *key, const char *in);
+void ceph_crypto_key_destroy(struct ceph_crypto_key *key);
+
+/* crypto.c */
+int ceph_crypt(const struct ceph_crypto_key *key, int usage_slot, bool encrypt,
+	       void *buf, int buf_len, int in_len, int *pout_len);
+int ceph_crypt_data_offset(const struct ceph_crypto_key *key);
+int ceph_crypt_buflen(const struct ceph_crypto_key *key, int data_len);
+void ceph_hmac_sha256(const struct ceph_crypto_key *key, const void *buf,
+		      int buf_len, u8 hmac[SHA256_DIGEST_SIZE]);
+int ceph_crypto_init(void);
+void ceph_crypto_shutdown(void);
+
+/* armor.c */
+int ceph_armor(char *dst, const char *src, const char *end);
+int ceph_unarmor(char *dst, const char *src, const char *end);
+
+#endif