1 files changed, 360 insertions, 0 deletions
diff --git a/src/runtime/mklockrank.go b/src/runtime/mklockrank.go
new file mode 100644
index 0000000000..0d50d60a22
--- /dev/null
+++ b/src/runtime/mklockrank.go
@@ -0,0 +1,360 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+
+// mklockrank records the static rank graph of the locks in the
+// runtime and generates the rank checking structures in lockrank.go.
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"internal/dag"
+	"io"
+	"log"
+	"os"
+	"strings"
+)
+
+// ranks describes the lock rank graph. See "go doc internal/dag" for
+// the syntax.
+//
+// "a < b" means a must be acquired before b if both are held
+// (or, if b is held, a cannot be acquired).
+//
+// "NONE < a" means no locks may be held when a is acquired.
+//
+// If a lock is not given a rank, then it is assumed to be a leaf
+// lock, which means no other lock can be acquired while it is held.
+// Therefore, leaf locks do not need to be given an explicit rank.
+//
+// Ranks in all caps are pseudo-nodes that help define order, but do
+// not actually define a rank.
+//
+// TODO: It's often hard to correlate rank names to locks. Change
+// these to be more consistent with the locks they label.
+const ranks = `
+# Sysmon
+NONE
+< sysmon
+< scavenge, forcegc;
+
+# Defer
+NONE < defer;
+
+# GC
+NONE <
+  sweepWaiters,
+  assistQueue,
+  sweep;
+
+# Scheduler, timers, netpoll
+NONE < pollDesc, cpuprof;
+assistQueue,
+  cpuprof,
+  forcegc,
+  pollDesc, # pollDesc can interact with timers, which can lock sched.
+  scavenge,
+  sweep,
+  sweepWaiters
+< sched;
+sched < allg, allp;
+allp < timers;
+timers < netpollInit;
+
+# Channels
+scavenge, sweep < hchan;
+NONE < notifyList;
+hchan, notifyList < sudog;
+
+# RWMutex
+NONE < rwmutexW;
+rwmutexW, sysmon < rwmutexR;
+
+# Semaphores
+NONE < root;
+
+# Itabs
+NONE
+< itab
+< reflectOffs;
+
+# Tracing without a P uses a global trace buffer.
+scavenge
+# Above TRACEGLOBAL can emit a trace event without a P.
+< TRACEGLOBAL
+# Below TRACEGLOBAL manages the global tracing buffer.
+# Note that traceBuf eventually chains to MALLOC, but we never get that far
+# in the situation where there's no P.
+< traceBuf;
+# Starting/stopping tracing traces strings.
+traceBuf < traceStrings;
+
+# Malloc
+allg,
+  hchan,
+  notifyList,
+  reflectOffs,
+  timers,
+  traceStrings
+# Above MALLOC are things that can allocate memory.
+< MALLOC
+# Below MALLOC is the malloc implementation.
+< fin,
+  gcBitsArenas,
+  mheapSpecial,
+  mspanSpecial,
+  spanSetSpine,
+  MPROF;
+
+# Memory profiling
+MPROF < profInsert, profBlock, profMemActive;
+profMemActive < profMemFuture;
+
+# Execution tracer events (with a P)
+hchan,
+  root,
+  sched,
+  traceStrings,
+  notifyList,
+  fin
+# Above TRACE is anything that can create a trace event
+< TRACE
+< trace
+< traceStackTab;
+
+# Stack allocation and copying
+gcBitsArenas,
+  netpollInit,
+  profBlock,
+  profInsert,
+  profMemFuture,
+  spanSetSpine,
+  traceStackTab
+# Anything that can grow the stack can acquire STACKGROW.
+# (Most higher layers imply STACKGROW, like MALLOC.)
+< STACKGROW
+# Below STACKGROW is the stack allocator/copying implementation.
+< gscan;
+gscan, rwmutexR < stackpool;
+gscan < stackLarge;
+# Generally, hchan must be acquired before gscan. But in one case,
+# where we suspend a G and then shrink its stack, syncadjustsudogs
+# can acquire hchan locks while holding gscan. To allow this case,
+# we use hchanLeaf instead of hchan.
+gscan < hchanLeaf;
+
+# Write barrier
+defer,
+  gscan,
+  mspanSpecial,
+  sudog
+# Anything that can have write barriers can acquire WB.
+# Above WB, we can have write barriers.
+< WB
+# Below WB is the write barrier implementation.
+< wbufSpans;
+
+# Span allocator
+stackLarge,
+  stackpool,
+  wbufSpans
+# Above mheap is anything that can call the span allocator.
+< mheap;
+# Below mheap is the span allocator implementation.
+mheap, mheapSpecial < globalAlloc;
+
+# panic is handled specially. It is implicitly below all other locks.
+NONE < panic;
+# deadlock is not acquired while holding panic, but it also needs to be
+# below all other locks.
+panic < deadlock;
+`
+
+// cyclicRanks lists lock ranks that allow multiple locks of the same
+// rank to be acquired simultaneously. The runtime enforces ordering
+// within these ranks using a separate mechanism.
+var cyclicRanks = map[string]bool{
+	// Multiple timers are locked simultaneously in destroy().
+	"timers": true,
+	// Multiple hchans are acquired in hchan.sortkey() order in
+	// select.
+	"hchan": true,
+	// Multiple hchanLeafs are acquired in hchan.sortkey() order in
+	// syncadjustsudogs().
+	"hchanLeaf": true,
+	// The point of the deadlock lock is to deadlock.
+	"deadlock": true,
+}
+
+func main() {
+	flagO := flag.String("o", "", "write to `file` instead of stdout")
+	flagDot := flag.Bool("dot", false, "emit graphviz output instead of Go")
+	flag.Parse()
+	if flag.NArg() != 0 {
+		fmt.Fprintf(os.Stderr, "too many arguments")
+		os.Exit(2)
+	}
+
+	g, err := dag.Parse(ranks)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var out []byte
+	if *flagDot {
+		var b bytes.Buffer
+		g.TransitiveReduction()
+		// Add cyclic edges for visualization.
+		for k := range cyclicRanks {
+			g.AddEdge(k, k)
+		}
+		// Reverse the graph. It's much easier to read this as
+		// a "<" partial order than a ">" partial order. This
+		// ways, locks are acquired from the top going down
+		// and time moves forward over the edges instead of
+		// backward.
+		g.Transpose()
+		generateDot(&b, g)
+		out = b.Bytes()
+	} else {
+		var b bytes.Buffer
+		generateGo(&b, g)
+		out, err = format.Source(b.Bytes())
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	if *flagO != "" {
+		err = os.WriteFile(*flagO, out, 0666)
+	} else {
+		_, err = os.Stdout.Write(out)
+	}
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func generateGo(w io.Writer, g *dag.Graph) {
+	fmt.Fprintf(w, `// Code generated by mklockrank.go; DO NOT EDIT.
+
+package runtime
+
+type lockRank int
+
+`)
+
+	// Create numeric ranks.
+	topo := g.Topo()
+	for i, j := 0, len(topo)-1; i < j; i, j = i+1, j-1 {
+		topo[i], topo[j] = topo[j], topo[i]
+	}
+	fmt.Fprintf(w, `
+// Constants representing the ranks of all non-leaf runtime locks, in rank order.
+// Locks with lower rank must be taken before locks with higher rank,
+// in addition to satisfying the partial order in lockPartialOrder.
+// A few ranks allow self-cycles, which are specified in lockPartialOrder.
+const (
+	lockRankUnknown lockRank = iota
+
+`)
+	for _, rank := range topo {
+		if isPseudo(rank) {
+			fmt.Fprintf(w, "\t// %s\n", rank)
+		} else {
+			fmt.Fprintf(w, "\t%s\n", cname(rank))
+		}
+	}
+	fmt.Fprintf(w, `)
+
+// lockRankLeafRank is the rank of lock that does not have a declared rank,
+// and hence is a leaf lock.
+const lockRankLeafRank lockRank = 1000
+`)
+
+	// Create string table.
+	fmt.Fprintf(w, `
+// lockNames gives the names associated with each of the above ranks.
+var lockNames = []string{
+`)
+	for _, rank := range topo {
+		if !isPseudo(rank) {
+			fmt.Fprintf(w, "\t%s: %q,\n", cname(rank), rank)
+		}
+	}
+	fmt.Fprintf(w, `}
+
+func (rank lockRank) String() string {
+	if rank == 0 {
+		return "UNKNOWN"
+	}
+	if rank == lockRankLeafRank {
+		return "LEAF"
+	}
+	if rank < 0 || int(rank) >= len(lockNames) {
+		return "BAD RANK"
+	}
+	return lockNames[rank]
+}
+`)
+
+	// Create partial order structure.
+	fmt.Fprintf(w, `
+// lockPartialOrder is the transitive closure of the lock rank graph.
+// An entry for rank X lists all of the ranks that can already be held
+// when rank X is acquired.
+//
+// Lock ranks that allow self-cycles list themselves.
+var lockPartialOrder [][]lockRank = [][]lockRank{
+`)
+	for _, rank := range topo {
+		if isPseudo(rank) {
+			continue
+		}
+		list := []string{}
+		for _, before := range g.Edges(rank) {
+			if !isPseudo(before) {
+				list = append(list, cname(before))
+			}
+		}
+		if cyclicRanks[rank] {
+			list = append(list, cname(rank))
+		}
+
+		fmt.Fprintf(w, "\t%s: {%s},\n", cname(rank), strings.Join(list, ", "))
+	}
+	fmt.Fprintf(w, "}\n")
+}
+
+// cname returns the Go const name for the given lock rank label.
+func cname(label string) string {
+	return "lockRank" + strings.ToUpper(label[:1]) + label[1:]
+}
+
+func isPseudo(label string) bool {
+	return strings.ToUpper(label) == label
+}
+
+// generateDot emits a Graphviz dot representation of g to w.
+func generateDot(w io.Writer, g *dag.Graph) {
+	fmt.Fprintf(w, "digraph g {\n")
+
+	// Define all nodes.
+	for _, node := range g.Nodes {
+		fmt.Fprintf(w, "%q;\n", node)
+	}
+
+	// Create edges.
+	for _, node := range g.Nodes {
+		for _, to := range g.Edges(node) {
+			fmt.Fprintf(w, "%q -> %q;\n", node, to)
+		}
+	}
+
+	fmt.Fprintf(w, "}\n")
+}