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, 189 insertions, 0 deletions

diff --git a/drivers/iommu/intel/trace.h b/drivers/iommu/intel/trace.h
new file mode 100644
index 000000000..9f0ab4353
--- /dev/null
+++ b/drivers/iommu/intel/trace.h
@@ -0,0 +1,189 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Intel IOMMU trace support
+ *
+ * Copyright (C) 2019 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@linux.intel.com>
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM intel_iommu
+
+#if !defined(_TRACE_INTEL_IOMMU_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_INTEL_IOMMU_H
+
+#include <linux/tracepoint.h>
+
+#include "iommu.h"
+
+#define MSG_MAX		256
+
+TRACE_EVENT(qi_submit,
+	TP_PROTO(struct intel_iommu *iommu, u64 qw0, u64 qw1, u64 qw2, u64 qw3),
+
+	TP_ARGS(iommu, qw0, qw1, qw2, qw3),
+
+	TP_STRUCT__entry(
+		__field(u64, qw0)
+		__field(u64, qw1)
+		__field(u64, qw2)
+		__field(u64, qw3)
+		__string(iommu, iommu->name)
+	),
+
+	TP_fast_assign(
+		__assign_str(iommu);
+		__entry->qw0 = qw0;
+		__entry->qw1 = qw1;
+		__entry->qw2 = qw2;
+		__entry->qw3 = qw3;
+	),
+
+	TP_printk("%s %s: 0x%llx 0x%llx 0x%llx 0x%llx",
+		  __print_symbolic(__entry->qw0 & 0xf,
+				   { QI_CC_TYPE,	"cc_inv" },
+				   { QI_IOTLB_TYPE,	"iotlb_inv" },
+				   { QI_DIOTLB_TYPE,	"dev_tlb_inv" },
+				   { QI_IEC_TYPE,	"iec_inv" },
+				   { QI_IWD_TYPE,	"inv_wait" },
+				   { QI_EIOTLB_TYPE,	"p_iotlb_inv" },
+				   { QI_PC_TYPE,	"pc_inv" },
+				   { QI_DEIOTLB_TYPE,	"p_dev_tlb_inv" },
+				   { QI_PGRP_RESP_TYPE,	"page_grp_resp" }),
+		__get_str(iommu),
+		__entry->qw0, __entry->qw1, __entry->qw2, __entry->qw3
+	)
+);
+
+TRACE_EVENT(prq_report,
+	TP_PROTO(struct intel_iommu *iommu, struct device *dev,
+		 u64 dw0, u64 dw1, u64 dw2, u64 dw3,
+		 unsigned long seq),
+
+	TP_ARGS(iommu, dev, dw0, dw1, dw2, dw3, seq),
+
+	TP_STRUCT__entry(
+		__field(u64, dw0)
+		__field(u64, dw1)
+		__field(u64, dw2)
+		__field(u64, dw3)
+		__field(unsigned long, seq)
+		__string(iommu, iommu->name)
+		__string(dev, dev_name(dev))
+		__dynamic_array(char, buff, MSG_MAX)
+	),
+
+	TP_fast_assign(
+		__entry->dw0 = dw0;
+		__entry->dw1 = dw1;
+		__entry->dw2 = dw2;
+		__entry->dw3 = dw3;
+		__entry->seq = seq;
+		__assign_str(iommu);
+		__assign_str(dev);
+	),
+
+	TP_printk("%s/%s seq# %ld: %s",
+		__get_str(iommu), __get_str(dev), __entry->seq,
+		decode_prq_descriptor(__get_str(buff), MSG_MAX, __entry->dw0,
+				      __entry->dw1, __entry->dw2, __entry->dw3)
+	)
+);
+
+DECLARE_EVENT_CLASS(cache_tag_log,
+	TP_PROTO(struct cache_tag *tag),
+	TP_ARGS(tag),
+	TP_STRUCT__entry(
+		__string(iommu, tag->iommu->name)
+		__string(dev, dev_name(tag->dev))
+		__field(u16, type)
+		__field(u16, domain_id)
+		__field(u32, pasid)
+		__field(u32, users)
+	),
+	TP_fast_assign(
+		__assign_str(iommu);
+		__assign_str(dev);
+		__entry->type = tag->type;
+		__entry->domain_id = tag->domain_id;
+		__entry->pasid = tag->pasid;
+		__entry->users = tag->users;
+	),
+	TP_printk("%s/%s type %s did %d pasid %d ref %d",
+		  __get_str(iommu), __get_str(dev),
+		  __print_symbolic(__entry->type,
+			{ CACHE_TAG_IOTLB,		"iotlb" },
+			{ CACHE_TAG_DEVTLB,		"devtlb" },
+			{ CACHE_TAG_NESTING_IOTLB,	"nesting_iotlb" },
+			{ CACHE_TAG_NESTING_DEVTLB,	"nesting_devtlb" }),
+		__entry->domain_id, __entry->pasid, __entry->users
+	)
+);
+
+DEFINE_EVENT(cache_tag_log, cache_tag_assign,
+	TP_PROTO(struct cache_tag *tag),
+	TP_ARGS(tag)
+);
+
+DEFINE_EVENT(cache_tag_log, cache_tag_unassign,
+	TP_PROTO(struct cache_tag *tag),
+	TP_ARGS(tag)
+);
+
+DECLARE_EVENT_CLASS(cache_tag_flush,
+	TP_PROTO(struct cache_tag *tag, unsigned long start, unsigned long end,
+		 unsigned long addr, unsigned long mask),
+	TP_ARGS(tag, start, end, addr, mask),
+	TP_STRUCT__entry(
+		__string(iommu, tag->iommu->name)
+		__string(dev, dev_name(tag->dev))
+		__field(u16, type)
+		__field(u16, domain_id)
+		__field(u32, pasid)
+		__field(unsigned long, start)
+		__field(unsigned long, end)
+		__field(unsigned long, addr)
+		__field(unsigned long, mask)
+	),
+	TP_fast_assign(
+		__assign_str(iommu);
+		__assign_str(dev);
+		__entry->type = tag->type;
+		__entry->domain_id = tag->domain_id;
+		__entry->pasid = tag->pasid;
+		__entry->start = start;
+		__entry->end = end;
+		__entry->addr = addr;
+		__entry->mask = mask;
+	),
+	TP_printk("%s %s[%d] type %s did %d [0x%lx-0x%lx] addr 0x%lx mask 0x%lx",
+		  __get_str(iommu), __get_str(dev), __entry->pasid,
+		  __print_symbolic(__entry->type,
+			{ CACHE_TAG_IOTLB,		"iotlb" },
+			{ CACHE_TAG_DEVTLB,		"devtlb" },
+			{ CACHE_TAG_NESTING_IOTLB,	"nesting_iotlb" },
+			{ CACHE_TAG_NESTING_DEVTLB,	"nesting_devtlb" }),
+		__entry->domain_id, __entry->start, __entry->end,
+		__entry->addr, __entry->mask
+	)
+);
+
+DEFINE_EVENT(cache_tag_flush, cache_tag_flush_range,
+	TP_PROTO(struct cache_tag *tag, unsigned long start, unsigned long end,
+		 unsigned long addr, unsigned long mask),
+	TP_ARGS(tag, start, end, addr, mask)
+);
+
+DEFINE_EVENT(cache_tag_flush, cache_tag_flush_range_np,
+	TP_PROTO(struct cache_tag *tag, unsigned long start, unsigned long end,
+		 unsigned long addr, unsigned long mask),
+	TP_ARGS(tag, start, end, addr, mask)
+);
+#endif /* _TRACE_INTEL_IOMMU_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_PATH ../../drivers/iommu/intel/
+#define TRACE_INCLUDE_FILE trace
+#include <trace/define_trace.h>