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, 120 insertions, 0 deletions

diff --git a/net/rds/ib_sysctl.c b/net/rds/ib_sysctl.c
new file mode 100644
index 000000000..2af678e71
--- /dev/null
+++ b/net/rds/ib_sysctl.c
@@ -0,0 +1,120 @@
+/*
+ * 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/kernel.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+
+#include "ib.h"
+
+static struct ctl_table_header *rds_ib_sysctl_hdr;
+
+unsigned long rds_ib_sysctl_max_send_wr = RDS_IB_DEFAULT_SEND_WR;
+unsigned long rds_ib_sysctl_max_recv_wr = RDS_IB_DEFAULT_RECV_WR;
+unsigned long rds_ib_sysctl_max_recv_allocation = (128 * 1024 * 1024) / RDS_FRAG_SIZE;
+static unsigned long rds_ib_sysctl_max_wr_min = 1;
+/* hardware will fail CQ creation long before this */
+static unsigned long rds_ib_sysctl_max_wr_max = (u32)~0;
+
+unsigned long rds_ib_sysctl_max_unsig_wrs = 16;
+static unsigned long rds_ib_sysctl_max_unsig_wr_min = 1;
+static unsigned long rds_ib_sysctl_max_unsig_wr_max = 64;
+
+/*
+ * This sysctl does nothing.
+ *
+ * Backwards compatibility with RDS 3.0 wire protocol
+ * disables initial FC credit exchange.
+ * If it's ever possible to drop 3.0 support,
+ * setting this to 1 and moving init/refill of send/recv
+ * rings from ib_cm_connect_complete() back into ib_setup_qp()
+ * will cause credits to be added before protocol negotiation.
+ */
+unsigned int rds_ib_sysctl_flow_control = 0;
+
+static struct ctl_table rds_ib_sysctl_table[] = {
+	{
+		.procname       = "max_send_wr",
+		.data		= &rds_ib_sysctl_max_send_wr,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_minmax,
+		.extra1		= &rds_ib_sysctl_max_wr_min,
+		.extra2		= &rds_ib_sysctl_max_wr_max,
+	},
+	{
+		.procname       = "max_recv_wr",
+		.data		= &rds_ib_sysctl_max_recv_wr,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_minmax,
+		.extra1		= &rds_ib_sysctl_max_wr_min,
+		.extra2		= &rds_ib_sysctl_max_wr_max,
+	},
+	{
+		.procname       = "max_unsignaled_wr",
+		.data		= &rds_ib_sysctl_max_unsig_wrs,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_minmax,
+		.extra1		= &rds_ib_sysctl_max_unsig_wr_min,
+		.extra2		= &rds_ib_sysctl_max_unsig_wr_max,
+	},
+	{
+		.procname       = "max_recv_allocation",
+		.data		= &rds_ib_sysctl_max_recv_allocation,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_minmax,
+	},
+	{
+		.procname	= "flow_control",
+		.data		= &rds_ib_sysctl_flow_control,
+		.maxlen		= sizeof(rds_ib_sysctl_flow_control),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+};
+
+void rds_ib_sysctl_exit(void)
+{
+	if (rds_ib_sysctl_hdr)
+		unregister_net_sysctl_table(rds_ib_sysctl_hdr);
+}
+
+int rds_ib_sysctl_init(void)
+{
+	rds_ib_sysctl_hdr = register_net_sysctl(&init_net, "net/rds/ib", rds_ib_sysctl_table);
+	if (!rds_ib_sysctl_hdr)
+		return -ENOMEM;
+	return 0;
+}