[dev.fuzz] internal/fuzz: don't count time spent loading corpus

The -fuzztime flag tells us how much time to spend fuzzing, not
counting time spent running the seed corpus. We shouldn't count time
spent loading the cache either. If the cache is large, the time limit
may be exceeded before the coordinator starts the workers.

Change-Id: If00435faa5d24aabdb9003ebb9337fa2e47f22b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/307310
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

2 files changed, 14 insertions, 11 deletions

diff --git a/src/internal/fuzz/fuzz.go b/src/internal/fuzz/fuzz.go
index 8e0425c0c4..293cb48d4d 100644
--- a/src/internal/fuzz/fuzz.go
+++ b/src/internal/fuzz/fuzz.go
@@ -18,6 +18,7 @@ import (
 	"reflect"
 	"runtime"
 	"strings"
+	"time"
 )
 
 // CoordinateFuzzing creates several worker processes and communicates with
@@ -27,6 +28,9 @@ import (
 // with the same arguments as the coordinator, except with the -test.fuzzworker
 // flag prepended to the argument list.
 //
+// timeout is the amount of wall clock time to spend fuzzing after the corpus
+// has loaded.
+//
 // parallel is the number of worker processes to run in parallel. If parallel
 // is 0, CoordinateFuzzing will run GOMAXPROCS workers.
 //
@@ -43,7 +47,7 @@ import (
 //
 // If a crash occurs, the function will return an error containing information
 // about the crash, which can be reported to the user.
-func CoordinateFuzzing(ctx context.Context, parallel int, seed []CorpusEntry, types []reflect.Type, corpusDir, cacheDir string) (err error) {
+func CoordinateFuzzing(ctx context.Context, timeout time.Duration, parallel int, seed []CorpusEntry, types []reflect.Type, corpusDir, cacheDir string) (err error) {
 	if err := ctx.Err(); err != nil {
 		return err
 	}
@@ -69,6 +73,12 @@ func CoordinateFuzzing(ctx context.Context, parallel int, seed []CorpusEntry, ty
 		corpus.entries = append(corpus.entries, CorpusEntry{Data: marshalCorpusFile(vals...), Values: vals})
 	}
 
+	if timeout > 0 {
+		var cancel func()
+		ctx, cancel = context.WithTimeout(ctx, timeout)
+		defer cancel()
+	}
+
 	// TODO(jayconrod): do we want to support fuzzing different binaries?
 	dir := "" // same as self
 	binPath := os.Args[0]
diff --git a/src/testing/internal/testdeps/deps.go b/src/testing/internal/testdeps/deps.go
index 8f587b2e1d..c77aca3da8 100644
--- a/src/testing/internal/testdeps/deps.go
+++ b/src/testing/internal/testdeps/deps.go
@@ -137,14 +137,9 @@ func (TestDeps) CoordinateFuzzing(timeout time.Duration, parallel int, seed []fu
 	// Fuzzing may be interrupted with a timeout or if the user presses ^C.
 	// In either case, we'll stop worker processes gracefully and save
 	// crashers and interesting values.
-	ctx, cancel := context.WithCancel(context.Background())
-	if timeout > 0 {
-		ctx, cancel = context.WithTimeout(ctx, timeout)
-	}
-	ctx, stop := signal.NotifyContext(ctx, os.Interrupt)
-	defer stop()
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
 	defer cancel()
-	err = fuzz.CoordinateFuzzing(ctx, parallel, seed, types, corpusDir, cacheDir)
+	err = fuzz.CoordinateFuzzing(ctx, timeout, parallel, seed, types, corpusDir, cacheDir)
 	if err == ctx.Err() {
 		return nil
 	}
@@ -158,9 +153,7 @@ func (TestDeps) RunFuzzWorker(fn func(fuzz.CorpusEntry) error) error {
 	// If the worker is interrupted, return quickly and without error.
 	// If only the coordinator process is interrupted, it tells each worker
 	// process to stop by closing its "fuzz_in" pipe.
-	ctx, cancel := context.WithCancel(context.Background())
-	ctx, stop := signal.NotifyContext(ctx, os.Interrupt)
-	defer stop()
+	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
 	defer cancel()
 	err := fuzz.RunFuzzWorker(ctx, fn)
 	if err == ctx.Err() {