cmd/go: revert 3 CLs affecting par.Work, context propagation, tracing

This reverts the following changes:

•	cmd/go: add tracing for querying and downloading from the proxy
	CL 242786, commit 1a3558341860357c2400e37773e5076bb3a51628

•	cmd/go: do context propagation for tracing downloads
	CL 248327, commit c0cf190d226cc3defb71d17c01d0b45bf49a8a85

•	cmd/go/internal: remove some users of par.Work
	CL 248326, commit f30044a03bc7cf107dbec03c02fb6d0072878252

Reason for revert: broke linux 386 and amd64 longtest builders.

The problem started with CL 248326, but CL 248327 and CL 242786
are reverted as well due to conflicts.

Updates #38714.
Fixes #40861.

Change-Id: I68496b4e5a27e47a42183553c3a645b288edac83
Reviewed-on: https://go-review.googlesource.com/c/go/+/249017
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

28 files changed, 216 insertions, 299 deletions

diff --git a/src/cmd/go/internal/get/get.go b/src/cmd/go/internal/get/get.go
index e5bacadaa3..ef43602aca 100644
--- a/src/cmd/go/internal/get/get.go
+++ b/src/cmd/go/internal/get/get.go
@@ -246,9 +246,9 @@ func download(arg string, parent *load.Package, stk *load.ImportStack, mode int)
 	load1 := func(path string, mode int) *load.Package {
 		if parent == nil {
 			mode := 0 // don't do module or vendor resolution
-			return load.LoadImport(context.TODO(), path, base.Cwd, nil, stk, nil, mode)
+			return load.LoadImport(path, base.Cwd, nil, stk, nil, mode)
 		}
-		return load.LoadImport(context.TODO(), path, parent.Dir, parent, stk, nil, mode|load.ResolveModule)
+		return load.LoadImport(path, parent.Dir, parent, stk, nil, mode|load.ResolveModule)
 	}
 
 	p := load1(arg, mode)
diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index e68c39f392..7303e6c866 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/src/cmd/go/internal/list/list.go
@@ -20,7 +20,6 @@ import (
 	"cmd/go/internal/cache"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/load"
-	"cmd/go/internal/modinfo"
 	"cmd/go/internal/modload"
 	"cmd/go/internal/str"
 	"cmd/go/internal/work"
@@ -350,7 +349,7 @@ func runList(ctx context.Context, cmd *base.Command, args []string) {
 		fm := template.FuncMap{
 			"join":    strings.Join,
 			"context": context,
-			"module":  func(path string) *modinfo.ModulePublic { return modload.ModuleInfo(ctx, path) },
+			"module":  modload.ModuleInfo,
 		}
 		tmpl, err := template.New("main").Funcs(fm).Parse(*listFmt)
 		if err != nil {
@@ -390,7 +389,7 @@ func runList(ctx context.Context, cmd *base.Command, args []string) {
 			base.Fatalf("go list -m: not using modules")
 		}
 
-		modload.InitMod(ctx) // Parses go.mod and sets cfg.BuildMod.
+		modload.InitMod() // Parses go.mod and sets cfg.BuildMod.
 		if cfg.BuildMod == "vendor" {
 			const actionDisabledFormat = "go list -m: can't %s using the vendor directory\n\t(Use -mod=mod or -mod=readonly to bypass.)"
 
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index 71fd9b5538..32c2ba7912 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -42,10 +42,10 @@ var (
 	ModBinDir            func() string                                                                            // return effective bin directory
 	ModLookup            func(parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) // lookup effective meaning of import
 	ModPackageModuleInfo func(path string) *modinfo.ModulePublic                                                  // return module info for Package struct
-	ModImportPaths       func(ctx context.Context, args []string) []*search.Match                                 // expand import paths
+	ModImportPaths       func(args []string) []*search.Match                                                      // expand import paths
 	ModPackageBuildInfo  func(main string, deps []string) string                                                  // return module info to embed in binary
 	ModInfoProg          func(info string, isgccgo bool) []byte                                                   // wrap module info in .go code for binary
-	ModImportFromFiles   func(context.Context, []string)                                                          // update go.mod to add modules for imports in these files
+	ModImportFromFiles   func([]string)                                                                           // update go.mod to add modules for imports in these files
 	ModDirImportPath     func(string) string                                                                      // return effective import path for directory
 )
 
@@ -553,7 +553,7 @@ func ReloadPackageNoFlags(arg string, stk *ImportStack) *Package {
 		})
 		packageDataCache.Delete(p.ImportPath)
 	}
-	return LoadImport(context.TODO(), arg, base.Cwd, nil, stk, nil, 0)
+	return LoadImport(arg, base.Cwd, nil, stk, nil, 0)
 }
 
 // dirToImportPath returns the pseudo-import path we use for a package
@@ -605,11 +605,11 @@ const (
 // LoadImport does not set tool flags and should only be used by
 // this package, as part of a bigger load operation, and by GOPATH-based "go get".
 // TODO(rsc): When GOPATH-based "go get" is removed, unexport this function.
-func LoadImport(ctx context.Context, path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
-	return loadImport(ctx, nil, path, srcDir, parent, stk, importPos, mode)
+func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
+	return loadImport(nil, path, srcDir, parent, stk, importPos, mode)
 }
 
-func loadImport(ctx context.Context, pre *preload, path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
+func loadImport(pre *preload, path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
 	if path == "" {
 		panic("LoadImport called with empty package path")
 	}
@@ -657,7 +657,7 @@ func loadImport(ctx context.Context, pre *preload, path, srcDir string, parent *
 		// Load package.
 		// loadPackageData may return bp != nil even if an error occurs,
 		// in order to return partial information.
-		p.load(ctx, path, stk, importPos, bp, err)
+		p.load(path, stk, importPos, bp, err)
 
 		if !cfg.ModulesEnabled && path != cleanImport(path) {
 			p.Error = &PackageError{
@@ -1591,7 +1591,7 @@ func (p *Package) DefaultExecName() string {
 // load populates p using information from bp, err, which should
 // be the result of calling build.Context.Import.
 // stk contains the import stack, not including path itself.
-func (p *Package) load(ctx context.Context, path string, stk *ImportStack, importPos []token.Position, bp *build.Package, err error) {
+func (p *Package) load(path string, stk *ImportStack, importPos []token.Position, bp *build.Package, err error) {
 	p.copyBuild(bp)
 
 	// The localPrefix is the path we interpret ./ imports relative to.
@@ -1800,7 +1800,7 @@ func (p *Package) load(ctx context.Context, path string, stk *ImportStack, impor
 		if path == "C" {
 			continue
 		}
-		p1 := LoadImport(ctx, path, p.Dir, p, stk, p.Internal.Build.ImportPos[path], ResolveImport)
+		p1 := LoadImport(path, p.Dir, p, stk, p.Internal.Build.ImportPos[path], ResolveImport)
 
 		path = p1.ImportPath
 		importPaths[i] = path
@@ -2073,7 +2073,7 @@ func PackageList(roots []*Package) []*Package {
 // TestPackageList returns the list of packages in the dag rooted at roots
 // as visited in a depth-first post-order traversal, including the test
 // imports of the roots. This ignores errors in test packages.
-func TestPackageList(ctx context.Context, roots []*Package) []*Package {
+func TestPackageList(roots []*Package) []*Package {
 	seen := map[*Package]bool{}
 	all := []*Package{}
 	var walk func(*Package)
@@ -2089,7 +2089,7 @@ func TestPackageList(ctx context.Context, roots []*Package) []*Package {
 	}
 	walkTest := func(root *Package, path string) {
 		var stk ImportStack
-		p1 := LoadImport(ctx, path, root.Dir, root, &stk, root.Internal.Build.TestImportPos[path], ResolveImport)
+		p1 := LoadImport(path, root.Dir, root, &stk, root.Internal.Build.TestImportPos[path], ResolveImport)
 		if p1.Error == nil {
 			walk(p1)
 		}
@@ -2112,7 +2112,7 @@ func TestPackageList(ctx context.Context, roots []*Package) []*Package {
 // TODO(jayconrod): delete this function and set flags automatically
 // in LoadImport instead.
 func LoadImportWithFlags(path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
-	p := LoadImport(context.TODO(), path, srcDir, parent, stk, importPos, mode)
+	p := LoadImport(path, srcDir, parent, stk, importPos, mode)
 	setToolFlags(p)
 	return p
 }
@@ -2153,12 +2153,12 @@ func PackagesAndErrors(ctx context.Context, patterns []string) []*Package {
 			// We need to test whether the path is an actual Go file and not a
 			// package path or pattern ending in '.go' (see golang.org/issue/34653).
 			if fi, err := os.Stat(p); err == nil && !fi.IsDir() {
-				return []*Package{GoFilesPackage(ctx, patterns)}
+				return []*Package{GoFilesPackage(patterns)}
 			}
 		}
 	}
 
-	matches := ImportPaths(ctx, patterns)
+	matches := ImportPaths(patterns)
 	var (
 		pkgs    []*Package
 		stk     ImportStack
@@ -2174,7 +2174,7 @@ func PackagesAndErrors(ctx context.Context, patterns []string) []*Package {
 			if pkg == "" {
 				panic(fmt.Sprintf("ImportPaths returned empty package for pattern %s", m.Pattern()))
 			}
-			p := loadImport(ctx, pre, pkg, base.Cwd, nil, &stk, nil, 0)
+			p := loadImport(pre, pkg, base.Cwd, nil, &stk, nil, 0)
 			p.Match = append(p.Match, m.Pattern())
 			p.Internal.CmdlinePkg = true
 			if m.IsLiteral() {
@@ -2228,9 +2228,9 @@ func setToolFlags(pkgs ...*Package) {
 	}
 }
 
-func ImportPaths(ctx context.Context, args []string) []*search.Match {
+func ImportPaths(args []string) []*search.Match {
 	if ModInit(); cfg.ModulesEnabled {
-		return ModImportPaths(ctx, args)
+		return ModImportPaths(args)
 	}
 	return search.ImportPaths(args)
 }
@@ -2281,7 +2281,7 @@ func PackagesForBuild(ctx context.Context, args []string) []*Package {
 // GoFilesPackage creates a package for building a collection of Go files
 // (typically named on the command line). The target is named p.a for
 // package p or named after the first Go file for package main.
-func GoFilesPackage(ctx context.Context, gofiles []string) *Package {
+func GoFilesPackage(gofiles []string) *Package {
 	ModInit()
 
 	for _, f := range gofiles {
@@ -2329,7 +2329,7 @@ func GoFilesPackage(ctx context.Context, gofiles []string) *Package {
 	ctxt.ReadDir = func(string) ([]os.FileInfo, error) { return dirent, nil }
 
 	if cfg.ModulesEnabled {
-		ModImportFromFiles(ctx, gofiles)
+		ModImportFromFiles(gofiles)
 	}
 
 	var err error
@@ -2345,7 +2345,7 @@ func GoFilesPackage(ctx context.Context, gofiles []string) *Package {
 	pkg := new(Package)
 	pkg.Internal.Local = true
 	pkg.Internal.CmdlineFiles = true
-	pkg.load(ctx, "command-line-arguments", &stk, nil, bp, err)
+	pkg.load("command-line-arguments", &stk, nil, bp, err)
 	pkg.Internal.LocalPrefix = dirToImportPath(dir)
 	pkg.ImportPath = "command-line-arguments"
 	pkg.Target = ""
diff --git a/src/cmd/go/internal/load/test.go b/src/cmd/go/internal/load/test.go
index a0e275095b..6db8a00245 100644
--- a/src/cmd/go/internal/load/test.go
+++ b/src/cmd/go/internal/load/test.go
@@ -108,7 +108,7 @@ func TestPackagesAndErrors(ctx context.Context, p *Package, cover *TestCover) (p
 	stk.Push(p.ImportPath + " (test)")
 	rawTestImports := str.StringList(p.TestImports)
 	for i, path := range p.TestImports {
-		p1 := loadImport(ctx, pre, path, p.Dir, p, &stk, p.Internal.Build.TestImportPos[path], ResolveImport)
+		p1 := loadImport(pre, path, p.Dir, p, &stk, p.Internal.Build.TestImportPos[path], ResolveImport)
 		if str.Contains(p1.Deps, p.ImportPath) || p1.ImportPath == p.ImportPath {
 			// Same error that loadPackage returns (via reusePackage) in pkg.go.
 			// Can't change that code, because that code is only for loading the
@@ -127,7 +127,7 @@ func TestPackagesAndErrors(ctx context.Context, p *Package, cover *TestCover) (p
 	pxtestNeedsPtest := false
 	rawXTestImports := str.StringList(p.XTestImports)
 	for i, path := range p.XTestImports {
-		p1 := loadImport(ctx, pre, path, p.Dir, p, &stk, p.Internal.Build.XTestImportPos[path], ResolveImport)
+		p1 := loadImport(pre, path, p.Dir, p, &stk, p.Internal.Build.XTestImportPos[path], ResolveImport)
 		if p1.ImportPath == p.ImportPath {
 			pxtestNeedsPtest = true
 		} else {
@@ -244,7 +244,7 @@ func TestPackagesAndErrors(ctx context.Context, p *Package, cover *TestCover) (p
 		if dep == ptest.ImportPath {
 			pmain.Internal.Imports = append(pmain.Internal.Imports, ptest)
 		} else {
-			p1 := loadImport(ctx, pre, dep, "", nil, &stk, nil, 0)
+			p1 := loadImport(pre, dep, "", nil, &stk, nil, 0)
 			pmain.Internal.Imports = append(pmain.Internal.Imports, p1)
 		}
 	}
diff --git a/src/cmd/go/internal/modcmd/download.go b/src/cmd/go/internal/modcmd/download.go
index 13e5cb066b..946e8ed3cf 100644
--- a/src/cmd/go/internal/modcmd/download.go
+++ b/src/cmd/go/internal/modcmd/download.go
@@ -5,15 +5,15 @@
 package modcmd
 
 import (
-	"cmd/go/internal/modfetch"
 	"context"
 	"encoding/json"
 	"os"
-	"runtime"
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/modfetch"
 	"cmd/go/internal/modload"
+	"cmd/go/internal/par"
 	"cmd/go/internal/work"
 
 	"golang.org/x/mod/module"
@@ -90,7 +90,7 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 	if len(args) == 0 {
 		args = []string{"all"}
 	} else if modload.HasModRoot() {
-		modload.InitMod(ctx) // to fill Target
+		modload.InitMod() // to fill Target
 		targetAtLatest := modload.Target.Path + "@latest"
 		targetAtUpgrade := modload.Target.Path + "@upgrade"
 		targetAtPatch := modload.Target.Path + "@patch"
@@ -102,7 +102,33 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 		}
 	}
 
-	downloadModule := func(m *moduleJSON) {
+	var mods []*moduleJSON
+	var work par.Work
+	listU := false
+	listVersions := false
+	for _, info := range modload.ListModules(ctx, args, listU, listVersions) {
+		if info.Replace != nil {
+			info = info.Replace
+		}
+		if info.Version == "" && info.Error == nil {
+			// main module or module replaced with file path.
+			// Nothing to download.
+			continue
+		}
+		m := &moduleJSON{
+			Path:    info.Path,
+			Version: info.Version,
+		}
+		mods = append(mods, m)
+		if info.Error != nil {
+			m.Error = info.Error.Err
+			continue
+		}
+		work.Add(m)
+	}
+
+	work.Do(10, func(item interface{}) {
+		m := item.(*moduleJSON)
 		var err error
 		m.Info, err = modfetch.InfoFile(m.Path, m.Version)
 		if err != nil {
@@ -120,53 +146,18 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 			return
 		}
 		mod := module.Version{Path: m.Path, Version: m.Version}
-		m.Zip, err = modfetch.DownloadZip(ctx, mod)
+		m.Zip, err = modfetch.DownloadZip(mod)
 		if err != nil {
 			m.Error = err.Error()
 			return
 		}
 		m.Sum = modfetch.Sum(mod)
-		m.Dir, err = modfetch.Download(ctx, mod)
+		m.Dir, err = modfetch.Download(mod)
 		if err != nil {
 			m.Error = err.Error()
 			return
 		}
-	}
-
-	var mods []*moduleJSON
-	listU := false
-	listVersions := false
-	type token struct{}
-	sem := make(chan token, runtime.GOMAXPROCS(0))
-	for _, info := range modload.ListModules(ctx, args, listU, listVersions) {
-		if info.Replace != nil {
-			info = info.Replace
-		}
-		if info.Version == "" && info.Error == nil {
-			// main module or module replaced with file path.
-			// Nothing to download.
-			continue
-		}
-		m := &moduleJSON{
-			Path:    info.Path,
-			Version: info.Version,
-		}
-		mods = append(mods, m)
-		if info.Error != nil {
-			m.Error = info.Error.Err
-			continue
-		}
-		sem <- token{}
-		go func() {
-			downloadModule(m)
-			<-sem
-		}()
-	}
-
-	// Fill semaphore channel to wait for goroutines to finish.
-	for n := cap(sem); n > 0; n-- {
-		sem <- token{}
-	}
+	})
 
 	if *downloadJSON {
 		for _, m := range mods {
diff --git a/src/cmd/go/internal/modcmd/graph.go b/src/cmd/go/internal/modcmd/graph.go
index 6da12b9cab..4853503fd4 100644
--- a/src/cmd/go/internal/modcmd/graph.go
+++ b/src/cmd/go/internal/modcmd/graph.go
@@ -15,6 +15,7 @@ import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/modload"
+	"cmd/go/internal/par"
 	"cmd/go/internal/work"
 
 	"golang.org/x/mod/module"
@@ -58,25 +59,23 @@ func runGraph(ctx context.Context, cmd *base.Command, args []string) {
 		return m.Path + "@" + m.Version
 	}
 
+	// Note: using par.Work only to manage work queue.
+	// No parallelism here, so no locking.
 	var out []string
 	var deps int // index in out where deps start
-	seen := map[module.Version]bool{modload.Target: true}
-	queue := []module.Version{modload.Target}
-	for len(queue) > 0 {
-		var m module.Version
-		m, queue = queue[0], queue[1:]
+	var work par.Work
+	work.Add(modload.Target)
+	work.Do(1, func(item interface{}) {
+		m := item.(module.Version)
 		list, _ := reqs.Required(m)
 		for _, r := range list {
-			if !seen[r] {
-				queue = append(queue, r)
-				seen[r] = true
-			}
+			work.Add(r)
 			out = append(out, format(m)+" "+format(r)+"\n")
 		}
 		if m == modload.Target {
 			deps = len(out)
 		}
-	}
+	})
 
 	sort.Slice(out[deps:], func(i, j int) bool {
 		return out[deps+i][0] < out[deps+j][0]
diff --git a/src/cmd/go/internal/modcmd/init.go b/src/cmd/go/internal/modcmd/init.go
index b6cffd332d..95063e62f4 100644
--- a/src/cmd/go/internal/modcmd/init.go
+++ b/src/cmd/go/internal/modcmd/init.go
@@ -51,6 +51,6 @@ func runInit(ctx context.Context, cmd *base.Command, args []string) {
 	if strings.Contains(modload.CmdModModule, "@") {
 		base.Fatalf("go mod init: module path must not contain '@'")
 	}
-	modload.InitMod(ctx) // does all the hard work
+	modload.InitMod() // does all the hard work
 	modload.WriteGoMod()
 }
diff --git a/src/cmd/go/internal/modcmd/tidy.go b/src/cmd/go/internal/modcmd/tidy.go
index c7c53d7c0c..769cd11fe8 100644
--- a/src/cmd/go/internal/modcmd/tidy.go
+++ b/src/cmd/go/internal/modcmd/tidy.go
@@ -40,7 +40,7 @@ func runTidy(ctx context.Context, cmd *base.Command, args []string) {
 		base.Fatalf("go mod tidy: no arguments allowed")
 	}
 
-	modload.LoadALL(ctx)
+	modload.LoadALL()
 	modload.TidyBuildList()
 	modload.TrimGoSum()
 	modload.WriteGoMod()
diff --git a/src/cmd/go/internal/modcmd/vendor.go b/src/cmd/go/internal/modcmd/vendor.go
index e5353b5c7f..257d1cd0ef 100644
--- a/src/cmd/go/internal/modcmd/vendor.go
+++ b/src/cmd/go/internal/modcmd/vendor.go
@@ -48,7 +48,7 @@ func runVendor(ctx context.Context, cmd *base.Command, args []string) {
 	if len(args) != 0 {
 		base.Fatalf("go mod vendor: vendor takes no arguments")
 	}
-	pkgs := modload.LoadVendor(ctx)
+	pkgs := modload.LoadVendor()
 
 	vdir := filepath.Join(modload.ModRoot(), "vendor")
 	if err := os.RemoveAll(vdir); err != nil {
diff --git a/src/cmd/go/internal/modcmd/why.go b/src/cmd/go/internal/modcmd/why.go
index da33fff89e..f400339b25 100644
--- a/src/cmd/go/internal/modcmd/why.go
+++ b/src/cmd/go/internal/modcmd/why.go
@@ -76,7 +76,7 @@ func runWhy(ctx context.Context, cmd *base.Command, args []string) {
 		}
 		mods := modload.ListModules(ctx, args, listU, listVersions)
 		byModule := make(map[module.Version][]string)
-		for _, path := range loadALL(ctx) {
+		for _, path := range loadALL() {
 			m := modload.PackageModule(path)
 			if m.Path != "" {
 				byModule[m] = append(byModule[m], path)
@@ -105,8 +105,8 @@ func runWhy(ctx context.Context, cmd *base.Command, args []string) {
 			sep = "\n"
 		}
 	} else {
-		matches := modload.ImportPaths(ctx, args) // resolve to packages
-		loadALL(ctx)                              // rebuild graph, from main module (not from named packages)
+		matches := modload.ImportPaths(args) // resolve to packages
+		loadALL()                            // rebuild graph, from main module (not from named packages)
 		sep := ""
 		for _, m := range matches {
 			for _, path := range m.Pkgs {
diff --git a/src/cmd/go/internal/modconv/convert.go b/src/cmd/go/internal/modconv/convert.go
index d5a0bc21e9..f465a9f395 100644
--- a/src/cmd/go/internal/modconv/convert.go
+++ b/src/cmd/go/internal/modconv/convert.go
@@ -7,12 +7,13 @@ package modconv
 import (
 	"fmt"
 	"os"
-	"runtime"
 	"sort"
 	"strings"
+	"sync"
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/modfetch"
+	"cmd/go/internal/par"
 
 	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/module"
@@ -41,52 +42,46 @@ func ConvertLegacyConfig(f *modfile.File, file string, data []byte) error {
 
 	// Convert requirements block, which may use raw SHA1 hashes as versions,
 	// to valid semver requirement list, respecting major versions.
-	versions := make([]*module.Version, len(mf.Require))
-	replace := make(map[string]*modfile.Replace)
+	var (
+		work    par.Work
+		mu      sync.Mutex
+		need    = make(map[string]string)
+		replace = make(map[string]*modfile.Replace)
+	)
 
 	for _, r := range mf.Replace {
 		replace[r.New.Path] = r
 		replace[r.Old.Path] = r
 	}
-
-	type token struct{}
-	sem := make(chan token, runtime.GOMAXPROCS(0))
-	for i, r := range mf.Require {
+	for _, r := range mf.Require {
 		m := r.Mod
 		if m.Path == "" {
 			continue
 		}
 		if re, ok := replace[m.Path]; ok {
-			m = re.New
+			work.Add(re.New)
+			continue
 		}
-		sem <- token{}
-		go func(i int, m module.Version) {
-			repo, info, err := modfetch.ImportRepoRev(m.Path, m.Version)
-			if err != nil {
-				fmt.Fprintf(os.Stderr, "go: converting %s: stat %s@%s: %v\n", base.ShortPath(file), m.Path, m.Version, err)
-				return
-			}
-
-			path := repo.ModulePath()
-			versions[i].Path = path
-			versions[i].Version = info.Version
-
-			<-sem
-		}(i, m)
-	}
-	// Fill semaphore channel to wait for all tasks to finish.
-	for n := cap(sem); n > 0; n-- {
-		sem <- token{}
+		work.Add(r.Mod)
 	}
 
-	need := map[string]string{}
-	for _, v := range versions {
+	work.Do(10, func(item interface{}) {
+		r := item.(module.Version)
+		repo, info, err := modfetch.ImportRepoRev(r.Path, r.Version)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "go: converting %s: stat %s@%s: %v\n", base.ShortPath(file), r.Path, r.Version, err)
+			return
+		}
+		mu.Lock()
+		path := repo.ModulePath()
 		// Don't use semver.Max here; need to preserve +incompatible suffix.
-		if needv, ok := need[v.Path]; !ok || semver.Compare(needv, v.Version) < 0 {
-			need[v.Path] = v.Version
+		if v, ok := need[path]; !ok || semver.Compare(v, info.Version) < 0 {
+			need[path] = info.Version
 		}
-	}
-	paths := make([]string, 0, len(need))
+		mu.Unlock()
+	})
+
+	var paths []string
 	for path := range need {
 		paths = append(paths, path)
 	}
diff --git a/src/cmd/go/internal/modconv/convert_test.go b/src/cmd/go/internal/modconv/convert_test.go
index faa2b4c606..a04a13b14f 100644
--- a/src/cmd/go/internal/modconv/convert_test.go
+++ b/src/cmd/go/internal/modconv/convert_test.go
@@ -6,7 +6,6 @@ package modconv
 
 import (
 	"bytes"
-	"context"
 	"fmt"
 	"internal/testenv"
 	"io/ioutil"
@@ -147,8 +146,6 @@ func TestConvertLegacyConfig(t *testing.T) {
 		},
 	}
 
-	ctx := context.Background()
-
 	for _, tt := range tests {
 		t.Run(strings.ReplaceAll(tt.path, "/", "_")+"_"+tt.vers, func(t *testing.T) {
 			f, err := modfile.Parse("golden", []byte(tt.gomod), nil)
@@ -160,7 +157,7 @@ func TestConvertLegacyConfig(t *testing.T) {
 				t.Fatal(err)
 			}
 
-			dir, err := modfetch.Download(ctx, module.Version{Path: tt.path, Version: tt.vers})
+			dir, err := modfetch.Download(module.Version{Path: tt.path, Version: tt.vers})
 			if err != nil {
 				t.Fatal(err)
 			}
diff --git a/src/cmd/go/internal/modfetch/fetch.go b/src/cmd/go/internal/modfetch/fetch.go
index e29eb0a942..e40158b535 100644
--- a/src/cmd/go/internal/modfetch/fetch.go
+++ b/src/cmd/go/internal/modfetch/fetch.go
@@ -7,7 +7,6 @@ package modfetch
 import (
 	"archive/zip"
 	"bytes"
-	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -24,7 +23,6 @@ import (
 	"cmd/go/internal/par"
 	"cmd/go/internal/renameio"
 	"cmd/go/internal/robustio"
-	"cmd/go/internal/trace"
 
 	"golang.org/x/mod/module"
 	"golang.org/x/mod/sumdb/dirhash"
@@ -36,7 +34,7 @@ var downloadCache par.Cache
 // Download downloads the specific module version to the
 // local download cache and returns the name of the directory
 // corresponding to the root of the module's file tree.
-func Download(ctx context.Context, mod module.Version) (dir string, err error) {
+func Download(mod module.Version) (dir string, err error) {
 	if cfg.GOMODCACHE == "" {
 		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
 		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
@@ -49,7 +47,7 @@ func Download(ctx context.Context, mod module.Version) (dir string, err error) {
 		err error
 	}
 	c := downloadCache.Do(mod, func() interface{} {
-		dir, err := download(ctx, mod)
+		dir, err := download(mod)
 		if err != nil {
 			return cached{"", err}
 		}
@@ -59,10 +57,7 @@ func Download(ctx context.Context, mod module.Version) (dir string, err error) {
 	return c.dir, c.err
 }
 
-func download(ctx context.Context, mod module.Version) (dir string, err error) {
-	ctx, span := trace.StartSpan(ctx, "modfetch.download "+mod.String())
-	defer span.Done()
-
+func download(mod module.Version) (dir string, err error) {
 	// If the directory exists, and no .partial file exists, the module has
 	// already been completely extracted. .partial files may be created when a
 	// module zip directory is extracted in place instead of being extracted to a
@@ -77,7 +72,7 @@ func download(ctx context.Context, mod module.Version) (dir string, err error) {
 	// To avoid cluttering the cache with extraneous files,
 	// DownloadZip uses the same lockfile as Download.
 	// Invoke DownloadZip before locking the file.
-	zipfile, err := DownloadZip(ctx, mod)
+	zipfile, err := DownloadZip(mod)
 	if err != nil {
 		return "", err
 	}
@@ -147,7 +142,6 @@ func download(ctx context.Context, mod module.Version) (dir string, err error) {
 		return "", err
 	}
 
-	ctx, span = trace.StartSpan(ctx, "unzip "+zipfile)
 	if unzipInPlace {
 		if err := ioutil.WriteFile(partialPath, nil, 0666); err != nil {
 			return "", err
@@ -177,7 +171,6 @@ func download(ctx context.Context, mod module.Version) (dir string, err error) {
 			return "", err
 		}
 	}
-	defer span.Done()
 
 	if !cfg.ModCacheRW {
 		// Make dir read-only only *after* renaming it.
@@ -202,7 +195,7 @@ var downloadZipCache par.Cache
 
 // DownloadZip downloads the specific module version to the
 // local zip cache and returns the name of the zip file.
-func DownloadZip(ctx context.Context, mod module.Version) (zipfile string, err error) {
+func DownloadZip(mod module.Version) (zipfile string, err error) {
 	// The par.Cache here avoids duplicate work.
 	type cached struct {
 		zipfile string
@@ -237,7 +230,7 @@ func DownloadZip(ctx context.Context, mod module.Version) (zipfile string, err e
 		if err := os.MkdirAll(filepath.Dir(zipfile), 0777); err != nil {
 			return cached{"", err}
 		}
-		if err := downloadZip(ctx, mod, zipfile); err != nil {
+		if err := downloadZip(mod, zipfile); err != nil {
 			return cached{"", err}
 		}
 		return cached{zipfile, nil}
@@ -245,10 +238,7 @@ func DownloadZip(ctx context.Context, mod module.Version) (zipfile string, err e
 	return c.zipfile, c.err
 }
 
-func downloadZip(ctx context.Context, mod module.Version, zipfile string) (err error) {
-	ctx, span := trace.StartSpan(ctx, "modfetch.downloadZip "+zipfile)
-	defer span.Done()
-
+func downloadZip(mod module.Version, zipfile string) (err error) {
 	// Clean up any remaining tempfiles from previous runs.
 	// This is only safe to do because the lock file ensures that their
 	// writers are no longer active.
diff --git a/src/cmd/go/internal/modfetch/zip_sum_test/zip_sum_test.go b/src/cmd/go/internal/modfetch/zip_sum_test/zip_sum_test.go
index 82398ebfed..eac9b32fa8 100644
--- a/src/cmd/go/internal/modfetch/zip_sum_test/zip_sum_test.go
+++ b/src/cmd/go/internal/modfetch/zip_sum_test/zip_sum_test.go
@@ -16,7 +16,6 @@
 package zip_sum_test
 
 import (
-	"context"
 	"crypto/sha256"
 	"encoding/csv"
 	"encoding/hex"
@@ -120,7 +119,7 @@ func TestZipSums(t *testing.T) {
 		name := fmt.Sprintf("%s@%s", strings.ReplaceAll(test.m.Path, "/", "_"), test.m.Version)
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
-			zipPath, err := modfetch.DownloadZip(context.Background(), test.m)
+			zipPath, err := modfetch.DownloadZip(test.m)
 			if err != nil {
 				if *updateTestData {
 					t.Logf("%s: could not download module: %s (will remove from testdata)", test.m, err)
diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index ee9757912b..93a6bb54d5 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -11,7 +11,6 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"runtime"
 	"sort"
 	"strings"
 	"sync"
@@ -22,6 +21,7 @@ import (
 	"cmd/go/internal/load"
 	"cmd/go/internal/modload"
 	"cmd/go/internal/mvs"
+	"cmd/go/internal/par"
 	"cmd/go/internal/search"
 	"cmd/go/internal/work"
 
@@ -353,7 +353,7 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 			if !strings.Contains(path, "...") {
 				m := search.NewMatch(path)
 				if pkgPath := modload.DirImportPath(path); pkgPath != "." {
-					m = modload.TargetPackages(ctx, pkgPath)
+					m = modload.TargetPackages(pkgPath)
 				}
 				if len(m.Pkgs) == 0 {
 					for _, err := range m.Errs {
@@ -399,7 +399,7 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 		default:
 			// The argument is a package or module path.
 			if modload.HasModRoot() {
-				if m := modload.TargetPackages(ctx, path); len(m.Pkgs) != 0 {
+				if m := modload.TargetPackages(path); len(m.Pkgs) != 0 {
 					// The path is in the main module. Nothing to query.
 					if vers != "upgrade" && vers != "patch" {
 						base.Errorf("go get %s: can't request explicit version of path in main module", arg)
@@ -491,7 +491,7 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 		if q.path == q.m.Path {
 			wg.Add(1)
 			go func(q *query) {
-				if hasPkg, err := modload.ModuleHasRootPackage(ctx, q.m); err != nil {
+				if hasPkg, err := modload.ModuleHasRootPackage(q.m); err != nil {
 					base.Errorf("go get: %v", err)
 				} else if !hasPkg {
 					modOnlyMu.Lock()
@@ -536,7 +536,7 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 			// Don't load packages if pkgPatterns is empty. Both
 			// modload.ImportPathsQuiet and ModulePackages convert an empty list
 			// of patterns to []string{"."}, which is not what we want.
-			matches = modload.ImportPathsQuiet(ctx, pkgPatterns, imports.AnyTags())
+			matches = modload.ImportPathsQuiet(pkgPatterns, imports.AnyTags())
 			seenPkgs = make(map[string]bool)
 			for i, match := range matches {
 				arg := pkgGets[i]
@@ -725,44 +725,29 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 // reported. A map from module paths to queries is returned, which includes
 // queries and modOnly.
 func runQueries(ctx context.Context, cache map[querySpec]*query, queries []*query, modOnly map[string]*query) map[string]*query {
+	var lookup par.Work
+	for _, q := range queries {
+		if cached := cache[q.querySpec]; cached != nil {
+			*q = *cached
+		} else {
+			cache[q.querySpec] = q
+			lookup.Add(q)
+		}
+	}
 
-	runQuery := func(q *query) {
+	lookup.Do(10, func(item interface{}) {
+		q := item.(*query)
 		if q.vers == "none" {
 			// Wait for downgrade step.
 			q.m = module.Version{Path: q.path, Version: "none"}
 			return
 		}
-		m, err := getQuery(ctx, q.path, q.vers, q.prevM, q.forceModulePath)
+		m, err := getQuery(q.path, q.vers, q.prevM, q.forceModulePath)
 		if err != nil {
 			base.Errorf("go get %s: %v", q.arg, err)
 		}
 		q.m = m
-	}
-
-	type token struct{}
-	sem := make(chan token, runtime.GOMAXPROCS(0))
-	for _, q := range queries {
-		if cached := cache[q.querySpec]; cached != nil {
-			*q = *cached
-		} else {
-			sem <- token{}
-			go func(q *query) {
-				runQuery(q)
-				<-sem
-			}(q)
-		}
-	}
-
-	// Fill semaphore channel to wait for goroutines to finish.
-	for n := cap(sem); n > 0; n-- {
-		sem <- token{}
-	}
-
-	// Add to cache after concurrent section to avoid races...
-	for _, q := range queries {
-		cache[q.querySpec] = q
-	}
-
+	})
 	base.ExitIfErrors()
 
 	byPath := make(map[string]*query)
@@ -790,7 +775,7 @@ func runQueries(ctx context.Context, cache map[querySpec]*query, queries []*quer
 // to determine the underlying module version being requested.
 // If forceModulePath is set, getQuery must interpret path
 // as a module path.
-func getQuery(ctx context.Context, path, vers string, prevM module.Version, forceModulePath bool) (module.Version, error) {
+func getQuery(path, vers string, prevM module.Version, forceModulePath bool) (module.Version, error) {
 	if (prevM.Version != "") != forceModulePath {
 		// We resolve package patterns by calling QueryPattern, which does not
 		// accept a previous version and therefore cannot take it into account for
@@ -812,7 +797,7 @@ func getQuery(ctx context.Context, path, vers string, prevM module.Version, forc
 			}
 		}
 
-		info, err := modload.Query(ctx, path, vers, prevM.Version, modload.Allowed)
+		info, err := modload.Query(path, vers, prevM.Version, modload.Allowed)
 		if err == nil {
 			if info.Version != vers && info.Version != prevM.Version {
 				logOncef("go: %s %s => %s", path, vers, info.Version)
@@ -838,7 +823,7 @@ func getQuery(ctx context.Context, path, vers string, prevM module.Version, forc
 	// If it turns out to only exist as a module, we can detect the resulting
 	// PackageNotInModuleError and avoid a second round-trip through (potentially)
 	// all of the configured proxies.
-	results, err := modload.QueryPattern(ctx, path, vers, modload.Allowed)
+	results, err := modload.QueryPattern(path, vers, modload.Allowed)
 	if err != nil {
 		// If the path doesn't contain a wildcard, check whether it was actually a
 		// module path instead. If so, return that.
@@ -994,7 +979,7 @@ func (u *upgrader) Upgrade(m module.Version) (module.Version, error) {
 	// If we're querying "upgrade" or "patch", Query will compare the current
 	// version against the chosen version and will return the current version
 	// if it is newer.
-	info, err := modload.Query(context.TODO(), m.Path, string(getU), m.Version, modload.Allowed)
+	info, err := modload.Query(m.Path, string(getU), m.Version, modload.Allowed)
 	if err != nil {
 		// Report error but return m, to let version selection continue.
 		// (Reporting the error will fail the command at the next base.ExitIfErrors.)
diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index a101681a1f..5f8a2e7e05 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -6,7 +6,6 @@ package modload
 
 import (
 	"bytes"
-	"context"
 	"encoding/hex"
 	"fmt"
 	"internal/goroot"
@@ -58,21 +57,21 @@ func PackageModuleInfo(pkgpath string) *modinfo.ModulePublic {
 	if !ok {
 		return nil
 	}
-	return moduleInfo(context.TODO(), m, true)
+	return moduleInfo(m, true)
 }
 
-func ModuleInfo(ctx context.Context, path string) *modinfo.ModulePublic {
+func ModuleInfo(path string) *modinfo.ModulePublic {
 	if !Enabled() {
 		return nil
 	}
 
 	if i := strings.Index(path, "@"); i >= 0 {
-		return moduleInfo(ctx, module.Version{Path: path[:i], Version: path[i+1:]}, false)
+		return moduleInfo(module.Version{Path: path[:i], Version: path[i+1:]}, false)
 	}
 
 	for _, m := range BuildList() {
 		if m.Path == path {
-			return moduleInfo(ctx, m, true)
+			return moduleInfo(m, true)
 		}
 	}
 
@@ -85,12 +84,12 @@ func ModuleInfo(ctx context.Context, path string) *modinfo.ModulePublic {
 }
 
 // addUpdate fills in m.Update if an updated version is available.
-func addUpdate(ctx context.Context, m *modinfo.ModulePublic) {
+func addUpdate(m *modinfo.ModulePublic) {
 	if m.Version == "" {
 		return
 	}
 
-	if info, err := Query(ctx, m.Path, "upgrade", m.Version, Allowed); err == nil && semver.Compare(info.Version, m.Version) > 0 {
+	if info, err := Query(m.Path, "upgrade", m.Version, Allowed); err == nil && semver.Compare(info.Version, m.Version) > 0 {
 		m.Update = &modinfo.ModulePublic{
 			Path:    m.Path,
 			Version: info.Version,
@@ -104,7 +103,7 @@ func addVersions(m *modinfo.ModulePublic) {
 	m.Versions, _ = versions(m.Path)
 }
 
-func moduleInfo(ctx context.Context, m module.Version, fromBuildList bool) *modinfo.ModulePublic {
+func moduleInfo(m module.Version, fromBuildList bool) *modinfo.ModulePublic {
 	if m == Target {
 		info := &modinfo.ModulePublic{
 			Path:    m.Path,
@@ -133,7 +132,7 @@ func moduleInfo(ctx context.Context, m module.Version, fromBuildList bool) *modi
 	// completeFromModCache fills in the extra fields in m using the module cache.
 	completeFromModCache := func(m *modinfo.ModulePublic) {
 		if m.Version != "" {
-			if q, err := Query(ctx, m.Path, m.Version, "", nil); err != nil {
+			if q, err := Query(m.Path, m.Version, "", nil); err != nil {
 				m.Error = &modinfo.ModuleError{Err: err.Error()}
 			} else {
 				m.Version = q.Version
diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index 5c51a79124..4d2bc805e2 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"go/build"
@@ -111,7 +110,7 @@ var _ load.ImportPathError = &AmbiguousImportError{}
 // Import returns an ImportMissingError as the error.
 // If Import can identify a module that could be added to supply the package,
 // the ImportMissingError records that module.
-func Import(ctx context.Context, path string) (m module.Version, dir string, err error) {
+func Import(path string) (m module.Version, dir string, err error) {
 	if strings.Contains(path, "@") {
 		return module.Version{}, "", fmt.Errorf("import path should not have @version")
 	}
@@ -166,7 +165,7 @@ func Import(ctx context.Context, path string) (m module.Version, dir string, err
 			// Avoid possibly downloading irrelevant modules.
 			continue
 		}
-		root, isLocal, err := fetch(ctx, m)
+		root, isLocal, err := fetch(m)
 		if err != nil {
 			// Report fetch error.
 			// Note that we don't know for sure this module is necessary,
@@ -249,7 +248,7 @@ func Import(ctx context.Context, path string) (m module.Version, dir string, err
 			return len(mods[i].Path) > len(mods[j].Path)
 		})
 		for _, m := range mods {
-			root, isLocal, err := fetch(ctx, m)
+			root, isLocal, err := fetch(m)
 			if err != nil {
 				// Report fetch error as above.
 				return module.Version{}, "", err
@@ -286,7 +285,7 @@ func Import(ctx context.Context, path string) (m module.Version, dir string, err
 
 	fmt.Fprintf(os.Stderr, "go: finding module for package %s\n", path)
 
-	candidates, err := QueryPackage(ctx, path, "latest", Allowed)
+	candidates, err := QueryPackage(path, "latest", Allowed)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			// Return "cannot find module providing package […]" instead of whatever
diff --git a/src/cmd/go/internal/modload/import_test.go b/src/cmd/go/internal/modload/import_test.go
index 47ce89a084..accc60eecd 100644
--- a/src/cmd/go/internal/modload/import_test.go
+++ b/src/cmd/go/internal/modload/import_test.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"internal/testenv"
 	"regexp"
 	"strings"
@@ -50,12 +49,10 @@ func TestImport(t *testing.T) {
 	}(allowMissingModuleImports)
 	AllowMissingModuleImports()
 
-	ctx := context.Background()
-
 	for _, tt := range importTests {
 		t.Run(strings.ReplaceAll(tt.path, "/", "_"), func(t *testing.T) {
 			// Note that there is no build list, so Import should always fail.
-			m, dir, err := Import(ctx, tt.path)
+			m, dir, err := Import(tt.path)
 			if err == nil {
 				t.Fatalf("Import(%q) = %v, %v, nil; expected error", tt.path, m, dir)
 			}
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 93027c44c4..fff060e665 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -6,7 +6,6 @@ package modload
 
 import (
 	"bytes"
-	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -333,7 +332,7 @@ func die() {
 //
 // As a side-effect, InitMod sets a default for cfg.BuildMod if it does not
 // already have an explicit value.
-func InitMod(ctx context.Context) {
+func InitMod() {
 	if len(buildList) > 0 {
 		return
 	}
@@ -360,7 +359,7 @@ func InitMod(ctx context.Context) {
 	}
 
 	var fixed bool
-	f, err := modfile.Parse(gomod, data, fixVersion(ctx, &fixed))
+	f, err := modfile.Parse(gomod, data, fixVersion(&fixed))
 	if err != nil {
 		// Errors returned by modfile.Parse begin with file:line.
 		base.Fatalf("go: errors parsing go.mod:\n%s\n", err)
@@ -398,7 +397,7 @@ func InitMod(ctx context.Context) {
 // and does nothing for versions that already appear to be canonical.
 //
 // The VersionFixer sets 'fixed' if it ever returns a non-canonical version.
-func fixVersion(ctx context.Context, fixed *bool) modfile.VersionFixer {
+func fixVersion(fixed *bool) modfile.VersionFixer {
 	return func(path, vers string) (resolved string, err error) {
 		defer func() {
 			if err == nil && resolved != vers {
@@ -430,7 +429,7 @@ func fixVersion(ctx context.Context, fixed *bool) modfile.VersionFixer {
 			}
 		}
 
-		info, err := Query(ctx, path, vers, "", nil)
+		info, err := Query(path, vers, "", nil)
 		if err != nil {
 			return "", err
 		}
diff --git a/src/cmd/go/internal/modload/list.go b/src/cmd/go/internal/modload/list.go
index 7bf4e86c8d..4768516e90 100644
--- a/src/cmd/go/internal/modload/list.go
+++ b/src/cmd/go/internal/modload/list.go
@@ -9,12 +9,12 @@ import (
 	"errors"
 	"fmt"
 	"os"
-	"runtime"
 	"strings"
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/modinfo"
+	"cmd/go/internal/par"
 	"cmd/go/internal/search"
 
 	"golang.org/x/mod/module"
@@ -22,42 +22,31 @@ import (
 
 func ListModules(ctx context.Context, args []string, listU, listVersions bool) []*modinfo.ModulePublic {
 	mods := listModules(ctx, args, listVersions)
-
-	type token struct{}
-	sem := make(chan token, runtime.GOMAXPROCS(0))
 	if listU || listVersions {
+		var work par.Work
 		for _, m := range mods {
-			add := func(m *modinfo.ModulePublic) {
-				sem <- token{}
-				go func() {
-					if listU {
-						addUpdate(ctx, m)
-					}
-					if listVersions {
-						addVersions(m)
-					}
-					<-sem
-				}()
-			}
-
-			add(m)
+			work.Add(m)
 			if m.Replace != nil {
-				add(m.Replace)
+				work.Add(m.Replace)
 			}
 		}
+		work.Do(10, func(item interface{}) {
+			m := item.(*modinfo.ModulePublic)
+			if listU {
+				addUpdate(m)
+			}
+			if listVersions {
+				addVersions(m)
+			}
+		})
 	}
-	// Fill semaphore channel to wait for all tasks to finish.
-	for n := cap(sem); n > 0; n-- {
-		sem <- token{}
-	}
-
 	return mods
 }
 
 func listModules(ctx context.Context, args []string, listVersions bool) []*modinfo.ModulePublic {
 	LoadBuildList(ctx)
 	if len(args) == 0 {
-		return []*modinfo.ModulePublic{moduleInfo(ctx, buildList[0], true)}
+		return []*modinfo.ModulePublic{moduleInfo(buildList[0], true)}
 	}
 
 	var mods []*modinfo.ModulePublic
@@ -83,7 +72,7 @@ func listModules(ctx context.Context, args []string, listVersions bool) []*modin
 				}
 			}
 
-			info, err := Query(ctx, path, vers, current, nil)
+			info, err := Query(path, vers, current, nil)
 			if err != nil {
 				mods = append(mods, &modinfo.ModulePublic{
 					Path:    path,
@@ -92,7 +81,7 @@ func listModules(ctx context.Context, args []string, listVersions bool) []*modin
 				})
 				continue
 			}
-			mods = append(mods, moduleInfo(ctx, module.Version{Path: path, Version: info.Version}, false))
+			mods = append(mods, moduleInfo(module.Version{Path: path, Version: info.Version}, false))
 			continue
 		}
 
@@ -117,7 +106,7 @@ func listModules(ctx context.Context, args []string, listVersions bool) []*modin
 				matched = true
 				if !matchedBuildList[i] {
 					matchedBuildList[i] = true
-					mods = append(mods, moduleInfo(ctx, m, true))
+					mods = append(mods, moduleInfo(m, true))
 				}
 			}
 		}
@@ -127,9 +116,9 @@ func listModules(ctx context.Context, args []string, listVersions bool) []*modin
 					// Don't make the user provide an explicit '@latest' when they're
 					// explicitly asking what the available versions are.
 					// Instead, resolve the module, even if it isn't an existing dependency.
-					info, err := Query(ctx, arg, "latest", "", nil)
+					info, err := Query(arg, "latest", "", nil)
 					if err == nil {
-						mods = append(mods, moduleInfo(ctx, module.Version{Path: arg, Version: info.Version}, false))
+						mods = append(mods, moduleInfo(module.Version{Path: arg, Version: info.Version}, false))
 					} else {
 						mods = append(mods, &modinfo.ModulePublic{
 							Path:  arg,
diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 686d491219..8190009b23 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -52,8 +52,8 @@ var loaded *loader
 // ImportPaths returns the set of packages matching the args (patterns),
 // on the target platform. Modules may be added to the build list
 // to satisfy new imports.
-func ImportPaths(ctx context.Context, patterns []string) []*search.Match {
-	matches := ImportPathsQuiet(ctx, patterns, imports.Tags())
+func ImportPaths(patterns []string) []*search.Match {
+	matches := ImportPathsQuiet(patterns, imports.Tags())
 	search.WarnUnmatched(matches)
 	return matches
 }
@@ -62,7 +62,7 @@ func ImportPaths(ctx context.Context, patterns []string) []*search.Match {
 // no matches. It also lets the caller specify a set of build tags to match
 // packages. The build tags should typically be imports.Tags() or
 // imports.AnyTags(); a nil map has no special meaning.
-func ImportPathsQuiet(ctx context.Context, patterns []string, tags map[string]bool) []*search.Match {
+func ImportPathsQuiet(patterns []string, tags map[string]bool) []*search.Match {
 	updateMatches := func(matches []*search.Match, iterating bool) {
 		for _, m := range matches {
 			switch {
@@ -103,7 +103,7 @@ func ImportPathsQuiet(ctx context.Context, patterns []string, tags map[string]bo
 
 			case strings.Contains(m.Pattern(), "..."):
 				m.Errs = m.Errs[:0]
-				matchPackages(ctx, m, loaded.tags, includeStd, buildList)
+				matchPackages(m, loaded.tags, includeStd, buildList)
 
 			case m.Pattern() == "all":
 				loaded.testAll = true
@@ -111,7 +111,7 @@ func ImportPathsQuiet(ctx context.Context, patterns []string, tags map[string]bo
 					// Enumerate the packages in the main module.
 					// We'll load the dependencies as we find them.
 					m.Errs = m.Errs[:0]
-					matchPackages(ctx, m, loaded.tags, omitStd, []module.Version{Target})
+					matchPackages(m, loaded.tags, omitStd, []module.Version{Target})
 				} else {
 					// Starting with the packages in the main module,
 					// enumerate the full list of "all".
@@ -129,7 +129,7 @@ func ImportPathsQuiet(ctx context.Context, patterns []string, tags map[string]bo
 		}
 	}
 
-	InitMod(ctx)
+	InitMod()
 
 	var matches []*search.Match
 	for _, pattern := range search.CleanPatterns(patterns) {
@@ -338,8 +338,8 @@ func pathInModuleCache(dir string) string {
 
 // ImportFromFiles adds modules to the build list as needed
 // to satisfy the imports in the named Go source files.
-func ImportFromFiles(ctx context.Context, gofiles []string) {
-	InitMod(ctx)
+func ImportFromFiles(gofiles []string) {
+	InitMod()
 
 	tags := imports.Tags()
 	imports, testImports, err := imports.ScanFiles(gofiles, tags)
@@ -391,7 +391,7 @@ func DirImportPath(dir string) string {
 func LoadBuildList(ctx context.Context) []module.Version {
 	ctx, span := trace.StartSpan(ctx, "LoadBuildList")
 	defer span.Done()
-	InitMod(ctx)
+	InitMod()
 	ReloadBuildList()
 	WriteGoMod()
 	return buildList
@@ -409,20 +409,20 @@ func ReloadBuildList() []module.Version {
 // It adds modules to the build list as needed to satisfy new imports.
 // This set is useful for deciding whether a particular import is needed
 // anywhere in a module.
-func LoadALL(ctx context.Context) []string {
-	return loadAll(ctx, true)
+func LoadALL() []string {
+	return loadAll(true)
 }
 
 // LoadVendor is like LoadALL but only follows test dependencies
 // for tests in the main module. Tests in dependency modules are
 // ignored completely.
 // This set is useful for identifying the which packages to include in a vendor directory.
-func LoadVendor(ctx context.Context) []string {
-	return loadAll(ctx, false)
+func LoadVendor() []string {
+	return loadAll(false)
 }
 
-func loadAll(ctx context.Context, testAll bool) []string {
-	InitMod(ctx)
+func loadAll(testAll bool) []string {
+	InitMod()
 
 	loaded = newLoader(imports.AnyTags())
 	loaded.isALL = true
@@ -430,7 +430,7 @@ func loadAll(ctx context.Context, testAll bool) []string {
 	if !testAll {
 		loaded.testRoots = true
 	}
-	all := TargetPackages(ctx, "...")
+	all := TargetPackages("...")
 	loaded.load(func() []string { return all.Pkgs })
 	checkMultiplePaths()
 	WriteGoMod()
@@ -453,13 +453,13 @@ func loadAll(ctx context.Context, testAll bool) []string {
 // TargetPackages returns the list of packages in the target (top-level) module
 // matching pattern, which may be relative to the working directory, under all
 // build tag settings.
-func TargetPackages(ctx context.Context, pattern string) *search.Match {
+func TargetPackages(pattern string) *search.Match {
 	// TargetPackages is relative to the main module, so ensure that the main
 	// module is a thing that can contain packages.
 	ModRoot()
 
 	m := search.NewMatch(pattern)
-	matchPackages(ctx, m, imports.AnyTags(), omitStd, []module.Version{Target})
+	matchPackages(m, imports.AnyTags(), omitStd, []module.Version{Target})
 	return m
 }
 
@@ -817,8 +817,7 @@ func (ld *loader) doPkg(item interface{}) {
 			return
 		}
 
-		// TODO(matloob): Handle TODO context. This needs to be threaded through Do.
-		pkg.mod, pkg.dir, pkg.err = Import(context.TODO(), pkg.path)
+		pkg.mod, pkg.dir, pkg.err = Import(pkg.path)
 		if pkg.dir == "" {
 			return
 		}
diff --git a/src/cmd/go/internal/modload/mvs.go b/src/cmd/go/internal/modload/mvs.go
index 67eb2c2e19..5dd009d31d 100644
--- a/src/cmd/go/internal/modload/mvs.go
+++ b/src/cmd/go/internal/modload/mvs.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"os"
@@ -225,7 +224,7 @@ func (*mvsReqs) next(m module.Version) (module.Version, error) {
 //
 // The isLocal return value reports whether the replacement,
 // if any, is local to the filesystem.
-func fetch(ctx context.Context, mod module.Version) (dir string, isLocal bool, err error) {
+func fetch(mod module.Version) (dir string, isLocal bool, err error) {
 	if mod == Target {
 		return ModRoot(), true, nil
 	}
@@ -255,6 +254,6 @@ func fetch(ctx context.Context, mod module.Version) (dir string, isLocal bool, e
 		mod = r
 	}
 
-	dir, err = modfetch.Download(ctx, mod)
+	dir, err = modfetch.Download(mod)
 	return dir, false, err
 }
diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index e82eb1506f..acc886bf21 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"os"
@@ -19,7 +18,6 @@ import (
 	"cmd/go/internal/modfetch"
 	"cmd/go/internal/search"
 	"cmd/go/internal/str"
-	"cmd/go/internal/trace"
 
 	"golang.org/x/mod/module"
 	"golang.org/x/mod/semver"
@@ -57,10 +55,10 @@ import (
 //
 // If path is the path of the main module and the query is "latest",
 // Query returns Target.Version as the version.
-func Query(ctx context.Context, path, query, current string, allowed func(module.Version) bool) (*modfetch.RevInfo, error) {
+func Query(path, query, current string, allowed func(module.Version) bool) (*modfetch.RevInfo, error) {
 	var info *modfetch.RevInfo
 	err := modfetch.TryProxies(func(proxy string) (err error) {
-		info, err = queryProxy(ctx, proxy, path, query, current, allowed)
+		info, err = queryProxy(proxy, path, query, current, allowed)
 		return err
 	})
 	return info, err
@@ -77,10 +75,7 @@ func (queryDisabledError) Error() string {
 	return fmt.Sprintf("cannot query module due to -mod=%s\n\t(%s)", cfg.BuildMod, cfg.BuildModReason)
 }
 
-func queryProxy(ctx context.Context, proxy, path, query, current string, allowed func(module.Version) bool) (*modfetch.RevInfo, error) {
-	ctx, span := trace.StartSpan(ctx, "modload.queryProxy "+path+" "+query)
-	defer span.Done()
-
+func queryProxy(proxy, path, query, current string, allowed func(module.Version) bool) (*modfetch.RevInfo, error) {
 	if current != "" && !semver.IsValid(current) {
 		return nil, fmt.Errorf("invalid previous version %q", current)
 	}
@@ -248,7 +243,7 @@ func queryProxy(ctx context.Context, proxy, path, query, current string, allowed
 	if err != nil {
 		return nil, err
 	}
-	releases, prereleases, err := filterVersions(ctx, path, versions, ok, preferIncompatible)
+	releases, prereleases, err := filterVersions(path, versions, ok, preferIncompatible)
 	if err != nil {
 		return nil, err
 	}
@@ -332,7 +327,7 @@ func matchSemverPrefix(p, v string) bool {
 // 	1. versions that do not satisfy the 'ok' predicate, and
 // 	2. "+incompatible" versions, if a compatible one satisfies the predicate
 // 	   and the incompatible version is not preferred.
-func filterVersions(ctx context.Context, path string, versions []string, ok func(module.Version) bool, preferIncompatible bool) (releases, prereleases []string, err error) {
+func filterVersions(path string, versions []string, ok func(module.Version) bool, preferIncompatible bool) (releases, prereleases []string, err error) {
 	var lastCompatible string
 	for _, v := range versions {
 		if !ok(module.Version{Path: path, Version: v}) {
@@ -348,7 +343,7 @@ func filterVersions(ctx context.Context, path string, versions []string, ok func
 				// https://golang.org/issue/34165.) Note that we even prefer a
 				// compatible pre-release over an incompatible release.
 
-				ok, err := versionHasGoMod(ctx, module.Version{Path: path, Version: lastCompatible})
+				ok, err := versionHasGoMod(module.Version{Path: path, Version: lastCompatible})
 				if err != nil {
 					return nil, nil, err
 				}
@@ -385,12 +380,12 @@ type QueryResult struct {
 // If the package is in the main module, QueryPackage considers only the main
 // module and only the version "latest", without checking for other possible
 // modules.
-func QueryPackage(ctx context.Context, path, query string, allowed func(module.Version) bool) ([]QueryResult, error) {
+func QueryPackage(path, query string, allowed func(module.Version) bool) ([]QueryResult, error) {
 	m := search.NewMatch(path)
 	if m.IsLocal() || !m.IsLiteral() {
 		return nil, fmt.Errorf("pattern %s is not an importable package", path)
 	}
-	return QueryPattern(ctx, path, query, allowed)
+	return QueryPattern(path, query, allowed)
 }
 
 // QueryPattern looks up the module(s) containing at least one package matching
@@ -406,10 +401,7 @@ func QueryPackage(ctx context.Context, path, query string, allowed func(module.V
 // If any matching package is in the main module, QueryPattern considers only
 // the main module and only the version "latest", without checking for other
 // possible modules.
-func QueryPattern(ctx context.Context, pattern, query string, allowed func(module.Version) bool) ([]QueryResult, error) {
-	ctx, span := trace.StartSpan(ctx, "modload.QueryPattern "+pattern+" "+query)
-	defer span.Done()
-
+func QueryPattern(pattern, query string, allowed func(module.Version) bool) ([]QueryResult, error) {
 	base := pattern
 
 	firstError := func(m *search.Match) error {
@@ -425,7 +417,7 @@ func QueryPattern(ctx context.Context, pattern, query string, allowed func(modul
 		base = pathpkg.Dir(pattern[:i+3])
 		match = func(mod module.Version, root string, isLocal bool) *search.Match {
 			m := search.NewMatch(pattern)
-			matchPackages(ctx, m, imports.AnyTags(), omitStd, []module.Version{mod})
+			matchPackages(m, imports.AnyTags(), omitStd, []module.Version{mod})
 			return m
 		}
 	} else {
@@ -477,18 +469,15 @@ func QueryPattern(ctx context.Context, pattern, query string, allowed func(modul
 	}
 
 	err := modfetch.TryProxies(func(proxy string) error {
-		queryModule := func(ctx context.Context, path string) (r QueryResult, err error) {
-			ctx, span := trace.StartSpan(ctx, "modload.QueryPattern.queryModule ["+proxy+"] "+path)
-			defer span.Done()
-
+		queryModule := func(path string) (r QueryResult, err error) {
 			current := findCurrentVersion(path)
 			r.Mod.Path = path
-			r.Rev, err = queryProxy(ctx, proxy, path, query, current, allowed)
+			r.Rev, err = queryProxy(proxy, path, query, current, allowed)
 			if err != nil {
 				return r, err
 			}
 			r.Mod.Version = r.Rev.Version
-			root, isLocal, err := fetch(ctx, r.Mod)
+			root, isLocal, err := fetch(r.Mod)
 			if err != nil {
 				return r, err
 			}
@@ -509,7 +498,7 @@ func QueryPattern(ctx context.Context, pattern, query string, allowed func(modul
 		}
 
 		var err error
-		results, err = queryPrefixModules(ctx, candidateModules, queryModule)
+		results, err = queryPrefixModules(candidateModules, queryModule)
 		return err
 	})
 
@@ -553,10 +542,7 @@ type prefixResult struct {
 	err error
 }
 
-func queryPrefixModules(ctx context.Context, candidateModules []string, queryModule func(ctx context.Context, path string) (QueryResult, error)) (found []QueryResult, err error) {
-	ctx, span := trace.StartSpan(ctx, "modload.queryPrefixModules")
-	defer span.Done()
-
+func queryPrefixModules(candidateModules []string, queryModule func(path string) (QueryResult, error)) (found []QueryResult, err error) {
 	// If the path we're attempting is not in the module cache and we don't have a
 	// fetch result cached either, we'll end up making a (potentially slow)
 	// request to the proxy or (often even slower) the origin server.
@@ -569,9 +555,8 @@ func queryPrefixModules(ctx context.Context, candidateModules []string, queryMod
 	var wg sync.WaitGroup
 	wg.Add(len(candidateModules))
 	for i, p := range candidateModules {
-		ctx := trace.StartGoroutine(ctx)
 		go func(p string, r *result) {
-			r.QueryResult, r.err = queryModule(ctx, p)
+			r.QueryResult, r.err = queryModule(p)
 			wg.Done()
 		}(p, &results[i])
 	}
@@ -713,8 +698,8 @@ func (e *PackageNotInModuleError) ImportPath() string {
 }
 
 // ModuleHasRootPackage returns whether module m contains a package m.Path.
-func ModuleHasRootPackage(ctx context.Context, m module.Version) (bool, error) {
-	root, isLocal, err := fetch(ctx, m)
+func ModuleHasRootPackage(m module.Version) (bool, error) {
+	root, isLocal, err := fetch(m)
 	if err != nil {
 		return false, err
 	}
@@ -722,8 +707,8 @@ func ModuleHasRootPackage(ctx context.Context, m module.Version) (bool, error) {
 	return ok, err
 }
 
-func versionHasGoMod(ctx context.Context, m module.Version) (bool, error) {
-	root, _, err := fetch(ctx, m)
+func versionHasGoMod(m module.Version) (bool, error) {
+	root, _, err := fetch(m)
 	if err != nil {
 		return false, err
 	}
diff --git a/src/cmd/go/internal/modload/query_test.go b/src/cmd/go/internal/modload/query_test.go
index 77080e9b5b..247e4c40d2 100644
--- a/src/cmd/go/internal/modload/query_test.go
+++ b/src/cmd/go/internal/modload/query_test.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"internal/testenv"
 	"io/ioutil"
 	"log"
@@ -180,8 +179,6 @@ func TestQuery(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 	testenv.MustHaveExecPath(t, "git")
 
-	ctx := context.Background()
-
 	for _, tt := range queryTests {
 		allow := tt.allow
 		if allow == "" {
@@ -195,7 +192,7 @@ func TestQuery(t *testing.T) {
 		t.Run(strings.ReplaceAll(tt.path, "/", "_")+"/"+tt.query+"/"+tt.current+"/"+allow, func(t *testing.T) {
 			t.Parallel()
 
-			info, err := Query(ctx, tt.path, tt.query, tt.current, allowed)
+			info, err := Query(tt.path, tt.query, tt.current, allowed)
 			if tt.err != "" {
 				if err == nil {
 					t.Errorf("Query(%q, %q, %v) = %v, want error %q", tt.path, tt.query, allow, info.Version, tt.err)
diff --git a/src/cmd/go/internal/modload/search.go b/src/cmd/go/internal/modload/search.go
index a9bee0af4e..c28e7c0c1e 100644
--- a/src/cmd/go/internal/modload/search.go
+++ b/src/cmd/go/internal/modload/search.go
@@ -5,7 +5,6 @@
 package modload
 
 import (
-	"context"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -28,7 +27,7 @@ const (
 // matchPackages is like m.MatchPackages, but uses a local variable (rather than
 // a global) for tags, can include or exclude packages in the standard library,
 // and is restricted to the given list of modules.
-func matchPackages(ctx context.Context, m *search.Match, tags map[string]bool, filter stdFilter, modules []module.Version) {
+func matchPackages(m *search.Match, tags map[string]bool, filter stdFilter, modules []module.Version) {
 	m.Pkgs = []string{}
 
 	isMatch := func(string) bool { return true }
@@ -154,7 +153,7 @@ func matchPackages(ctx context.Context, m *search.Match, tags map[string]bool, f
 			isLocal = true
 		} else {
 			var err error
-			root, isLocal, err = fetch(ctx, mod)
+			root, isLocal, err = fetch(mod)
 			if err != nil {
 				m.AddError(err)
 				continue
diff --git a/src/cmd/go/internal/run/run.go b/src/cmd/go/internal/run/run.go
index 99578b244c..deec5106ff 100644
--- a/src/cmd/go/internal/run/run.go
+++ b/src/cmd/go/internal/run/run.go
@@ -77,7 +77,7 @@ func runRun(ctx context.Context, cmd *base.Command, args []string) {
 				base.Fatalf("go run: cannot run *_test.go files (%s)", file)
 			}
 		}
-		p = load.GoFilesPackage(ctx, files)
+		p = load.GoFilesPackage(files)
 	} else if len(args) > 0 && !strings.HasPrefix(args[0], "-") {
 		pkgs := load.PackagesAndErrors(ctx, args[:1])
 		if len(pkgs) == 0 {
diff --git a/src/cmd/go/internal/test/test.go b/src/cmd/go/internal/test/test.go
index 3aee6939d2..9cef8cf89c 100644
--- a/src/cmd/go/internal/test/test.go
+++ b/src/cmd/go/internal/test/test.go
@@ -702,7 +702,7 @@ func runTest(ctx context.Context, cmd *base.Command, args []string) {
 		}
 
 		// Select for coverage all dependencies matching the testCoverPaths patterns.
-		for _, p := range load.TestPackageList(ctx, pkgs) {
+		for _, p := range load.TestPackageList(pkgs) {
 			haveMatch := false
 			for i := range testCoverPaths {
 				if match[i](p) {
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index d975c36306..681ecd7646 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -2900,7 +2900,7 @@ func (b *Builder) swigDoIntSize(objdir string) (intsize string, err error) {
 	}
 	srcs := []string{src}
 
-	p := load.GoFilesPackage(context.TODO(), srcs)
+	p := load.GoFilesPackage(srcs)
 
 	if _, _, e := BuildToolchain.gc(b, &Action{Mode: "swigDoIntSize", Package: p, Objdir: objdir}, "", nil, "", false, srcs); e != nil {
 		return "32", nil