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, 155 insertions, 0 deletions

diff --git a/net/rds/stats.c b/net/rds/stats.c
new file mode 100644
index 000000000..24ee22d09
--- /dev/null
+++ b/net/rds/stats.c
@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2006 Oracle.  All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/percpu.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
+#include <linux/export.h>
+
+#include "rds.h"
+
+DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_statistics, rds_stats);
+EXPORT_PER_CPU_SYMBOL_GPL(rds_stats);
+
+/* :.,$s/unsigned long\>.*\<s_\(.*\);/"\1",/g */
+
+static const char *const rds_stat_names[] = {
+	"conn_reset",
+	"recv_drop_bad_checksum",
+	"recv_drop_old_seq",
+	"recv_drop_no_sock",
+	"recv_drop_dead_sock",
+	"recv_deliver_raced",
+	"recv_delivered",
+	"recv_queued",
+	"recv_immediate_retry",
+	"recv_delayed_retry",
+	"recv_ack_required",
+	"recv_rdma_bytes",
+	"recv_ping",
+	"send_queue_empty",
+	"send_queue_full",
+	"send_lock_contention",
+	"send_lock_queue_raced",
+	"send_immediate_retry",
+	"send_delayed_retry",
+	"send_drop_acked",
+	"send_ack_required",
+	"send_queued",
+	"send_rdma",
+	"send_rdma_bytes",
+	"send_pong",
+	"page_remainder_hit",
+	"page_remainder_miss",
+	"copy_to_user",
+	"copy_from_user",
+	"cong_update_queued",
+	"cong_update_received",
+	"cong_send_error",
+	"cong_send_blocked",
+	"recv_bytes_added_to_sock",
+	"recv_bytes_freed_fromsock",
+	"send_stuck_rm",
+	"mprds_catchup_tx0_retries",
+};
+
+void rds_stats_info_copy(struct rds_info_iterator *iter,
+			 uint64_t *values, const char *const *names, size_t nr)
+{
+	struct rds_info_counter ctr;
+	size_t i;
+
+	for (i = 0; i < nr; i++) {
+		BUG_ON(strlen(names[i]) >= sizeof(ctr.name));
+		strscpy_pad(ctr.name, names[i]);
+		ctr.value = values[i];
+
+		rds_info_copy(iter, &ctr, sizeof(ctr));
+	}
+}
+EXPORT_SYMBOL_GPL(rds_stats_info_copy);
+
+/*
+ * This gives global counters across all the transports.  The strings
+ * are copied in so that the tool doesn't need knowledge of the specific
+ * stats that we're exporting.  Some are pretty implementation dependent
+ * and may change over time.  That doesn't stop them from being useful.
+ *
+ * This is the only function in the chain that knows about the byte granular
+ * length in userspace.  It converts it to number of stat entries that the
+ * rest of the functions operate in.
+ */
+static void rds_stats_info(struct socket *sock, unsigned int len,
+			   struct rds_info_iterator *iter,
+			   struct rds_info_lengths *lens)
+{
+	struct rds_statistics stats = {0, };
+	uint64_t *src;
+	uint64_t *sum;
+	size_t i;
+	int cpu;
+	unsigned int avail;
+
+	avail = len / sizeof(struct rds_info_counter);
+
+	if (avail < ARRAY_SIZE(rds_stat_names)) {
+		avail = 0;
+		goto trans;
+	}
+
+	for_each_online_cpu(cpu) {
+		src = (uint64_t *)&(per_cpu(rds_stats, cpu));
+		sum = (uint64_t *)&stats;
+		for (i = 0; i < sizeof(stats) / sizeof(uint64_t); i++)
+			*(sum++) += *(src++);
+	}
+
+	rds_stats_info_copy(iter, (uint64_t *)&stats, rds_stat_names,
+			    ARRAY_SIZE(rds_stat_names));
+	avail -= ARRAY_SIZE(rds_stat_names);
+
+trans:
+	lens->each = sizeof(struct rds_info_counter);
+	lens->nr = rds_trans_stats_info_copy(iter, avail) +
+		   ARRAY_SIZE(rds_stat_names);
+}
+
+void rds_stats_exit(void)
+{
+	rds_info_deregister_func(RDS_INFO_COUNTERS, rds_stats_info);
+}
+
+int rds_stats_init(void)
+{
+	rds_info_register_func(RDS_INFO_COUNTERS, rds_stats_info);
+	return 0;
+}