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, 43 insertions, 0 deletions

diff --git a/arch/mips/kvm/interrupt.h b/arch/mips/kvm/interrupt.h
new file mode 100644
index 000000000..07bc0160b
--- /dev/null
+++ b/arch/mips/kvm/interrupt.h
@@ -0,0 +1,43 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * KVM/MIPS: Interrupts
+ * Copyright (C) 2012  MIPS Technologies, Inc.  All rights reserved.
+ * Authors: Sanjay Lal <sanjayl@kymasys.com>
+ */
+
+/*
+ * MIPS Exception Priorities, exceptions (including interrupts) are queued up
+ * for the guest in the order specified by their priorities
+ */
+
+#define MIPS_EXC_RESET              0
+#define MIPS_EXC_SRESET             1
+#define MIPS_EXC_DEBUG_ST           2
+#define MIPS_EXC_DEBUG              3
+#define MIPS_EXC_DDB                4
+#define MIPS_EXC_NMI                5
+#define MIPS_EXC_MCHK               6
+#define MIPS_EXC_INT_TIMER          7
+#define MIPS_EXC_INT_IO_1           8
+#define MIPS_EXC_INT_IO_2           9
+#define MIPS_EXC_EXECUTE            10
+#define MIPS_EXC_INT_IPI_1          11
+#define MIPS_EXC_INT_IPI_2          12
+#define MIPS_EXC_MAX                13
+/* XXXSL More to follow */
+
+#define C_TI        (_ULCAST_(1) << 30)
+
+extern u32 *kvm_priority_to_irq;
+u32 kvm_irq_to_priority(u32 irq);
+
+int kvm_mips_pending_timer(struct kvm_vcpu *vcpu);
+
+void kvm_mips_deliver_interrupts(struct kvm_vcpu *vcpu, u32 cause);
+
+#ifdef CONFIG_CPU_LOONGSON64
+extern void kvm_init_loongson_ipi(struct kvm *kvm);
+#endif