pkg/osutil: move Semaphore from pkg/instance

Semaphore is a very low-level primitive type,
while pkg/instance is a very high-level package with lots of deps.
Semaphore does not belong there, and may lead to cyclic deps
if we use it more. Move it to pkg/osutil. It's not really OS-specific,
but we don't have a better package.

Author: dvyukov

pkg/bisect/bisect.go

@@ -36,8 +36,8 @@ type Config struct {
 	Syzkaller       SyzkallerConfig
 	Repro           ReproConfig
 	Manager         *mgrconfig.Config
-	BuildSemaphore  *instance.Semaphore
-	TestSemaphore   *instance.Semaphore
+	BuildSemaphore  *osutil.Semaphore
+	TestSemaphore   *osutil.Semaphore
 	BuildCPUs       int
 	// CrossTree specifies whether a cross tree bisection is to take place, i.e.
 	// Kernel.Commit is not reachable from Kernel.Branch.

pkg/instance/instance.go

@@ -40,8 +40,8 @@ type Env interface {
 type env struct {
 	cfg           *mgrconfig.Config
 	optionalFlags bool
-	buildSem      *Semaphore
-	testSem       *Semaphore
+	buildSem      *osutil.Semaphore
+	testSem       *osutil.Semaphore
 }
 
 type BuildKernelConfig struct {
@@ -56,7 +56,7 @@ type BuildKernelConfig struct {
 	BuildCPUs    int
 }
 
-func NewEnv(cfg *mgrconfig.Config, buildSem, testSem *Semaphore) (Env, error) {
+func NewEnv(cfg *mgrconfig.Config, buildSem, testSem *osutil.Semaphore) (Env, error) {
 	if !vm.AllowsOvercommit(cfg.Type) {
 		return nil, fmt.Errorf("test instances are not supported for %v VMs", cfg.Type)
 	}
@@ -508,40 +508,6 @@ func RunnerCmd(prog, fwdAddr, os, arch string, poolIdx, vmIdx int, threaded, new
 		"-threaded=%t -new-env=%t", prog, fwdAddr, os, arch, poolIdx, vmIdx, threaded, newEnv)
 }
 
-type Semaphore struct {
-	ch chan struct{}
-}
-
-func NewSemaphore(count int) *Semaphore {
-	s := &Semaphore{
-		ch: make(chan struct{}, count),
-	}
-	for i := 0; i < count; i++ {
-		s.Signal()
-	}
-	return s
-}
-
-func (s *Semaphore) Wait() {
-	<-s.ch
-}
-
-func (s *Semaphore) WaitC() <-chan struct{} {
-	return s.ch
-}
-
-func (s *Semaphore) Available() int {
-	return len(s.ch)
-}
-
-func (s *Semaphore) Signal() {
-	if av := s.Available(); av == cap(s.ch) {
-		// Not super reliable, but let it be here just in case.
-		panic(fmt.Sprintf("semaphore capacity (%d) is exceeded (%d)", cap(s.ch), av))
-	}
-	s.ch <- struct{}{}
-}
-
 // RunSmokeTest executes syz-manager in the smoke test mode and returns two values:
 // The crash report, if the testing failed.
 // An error if there was a problem not related to testing the kernel.

pkg/osutil/semaphore.go

@@ -0,0 +1,42 @@
+// Copyright 2025 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package osutil
+
+import (
+	"fmt"
+)
+
+type Semaphore struct {
+	ch chan struct{}
+}
+
+func NewSemaphore(count int) *Semaphore {
+	s := &Semaphore{
+		ch: make(chan struct{}, count),
+	}
+	for i := 0; i < count; i++ {
+		s.Signal()
+	}
+	return s
+}
+
+func (s *Semaphore) Wait() {
+	<-s.ch
+}
+
+func (s *Semaphore) WaitC() <-chan struct{} {
+	return s.ch
+}
+
+func (s *Semaphore) Available() int {
+	return len(s.ch)
+}
+
+func (s *Semaphore) Signal() {
+	if av := s.Available(); av == cap(s.ch) {
+		// Not super reliable, but let it be here just in case.
+		panic(fmt.Sprintf("semaphore capacity (%v) is exceeded (%v)", cap(s.ch), av))
+	}
+	s.ch <- struct{}{}
+}

pkg/updater/updater.go

@@ -49,7 +49,7 @@ type Updater struct {
 type Config struct {
 	// If set, exit on updates instead of restarting the current binary.
 	ExitOnUpdate          bool
-	BuildSem              *instance.Semaphore
+	BuildSem              *osutil.Semaphore
 	ReportBuildError      func(commit *vcs.Commit, compilerID string, buildErr error)
 	SyzkallerRepo         string
 	SyzkallerBranch       string

syz-ci/manager.go

@@ -170,12 +170,12 @@ func createManager(cfg *Config, mgrcfg *ManagerConfig, debug bool) (*Manager, er
 // Gates kernel builds, syzkaller builds and coverage report generation.
 // Kernel builds take whole machine, so we don't run more than one at a time.
 // Also current image build script uses some global resources (/dev/nbd0) and can't run in parallel.
-var buildSem = instance.NewSemaphore(1)
+var buildSem = osutil.NewSemaphore(1)
 
 // Gates tests that require extra VMs.
 // Currently we overcommit instances in such cases, so we'd like to minimize the number of
 // simultaneous env.Test calls.
-var testSem = instance.NewSemaphore(1)
+var testSem = osutil.NewSemaphore(1)
 
 const fuzzingMinutesBeforeCover = 360
 const benchUploadPeriod = 30 * time.Minute