vm: check preemption string only for gce instances

Fixes google#5028

vm/gce/gce.go

@@ -36,8 +36,9 @@ import (
 
 func init() {
  vmimpl.Register("gce", vmimpl.Type{
- Ctor: ctor,
- Overcommit: true,
+ Ctor: ctor,
+ Overcommit: true,
+ Preemptible: true,
  })
 }
 

vm/vm.go

@@ -43,6 +43,7 @@ import (
 
 type Pool struct {
  impl vmimpl.Pool
+ typ vmimpl.Type
  workdir string
  template string
  timeouts targets.Timeouts
@@ -128,6 +129,7 @@ func Create(cfg *mgrconfig.Config, debug bool) (*Pool, error) {
  }
  return &Pool{
  impl: impl,
+ typ: typ,
  workdir: env.Workdir,
  template: cfg.WorkdirTemplate,
  timeouts: cfg.Timeouts,
@@ -420,7 +422,9 @@ func (mon *monitor) extractError(defaultError string) *report.Report {
  if defaultError != noOutputCrash || diagWait {
  mon.waitForOutput()
  }
- if bytes.Contains(mon.output, []byte(executorPreemptedStr)) {
+ // Check the executorPreemptedStr only for preemptible instances since executor can print
+ // the string spuriously in some cases (gets SIGTERM from test program somehow).
+ if mon.inst.pool.typ.Preemptible && bytes.Contains(mon.output, []byte(executorPreemptedStr)) {
  return nil
  }
  if defaultError == "" && mon.reporter.ContainsCrash(mon.output[mon.matchPos:]) {

vm/vmimpl/vmimpl.go

@@ -133,6 +133,10 @@ type Type struct {
  // It's possible to create out-of-thin-air instances of this type.
  // Out-of-thin-air instances are used by syz-ci for image testing, patch testing, bisection, etc.
  Overcommit bool
+ // Instances of this type can be preempted and lost connection as the result.
+ // For preempted instances executor prints "SYZ-EXECUTOR: PREEMPTED" and then
+ // the host understands that the lost connection was expected and is not a bug.
+ Preemptible bool
 }
 
 type ctorFunc func(env *Env) (Pool, error)