[dev.fuzz] internal/fuzz: don't store corpus in memory

Instead of holding all corpus data/values in memory, only store seed
inputs added via F.Add in memory, and only load corpus entries which
are written to disk when we need them. This should significantly reduce
the memory required by the coordinator process.

Additionally only load the corpus in the coordinator process, since the
worker has no need for it.

Fixes #46669.

Change-Id: Ic3b0c5e929fdb3e2877b963e6b0fa14e140c1e1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/345096
Trust: Roland Shoemaker <roland@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 23 insertions, 11 deletions

diff --git a/src/testing/fuzz.go b/src/testing/fuzz.go
index 4892d3f3e9..e567f7d9f4 100644
--- a/src/testing/fuzz.go
+++ b/src/testing/fuzz.go
@@ -305,21 +305,33 @@ func (f *F) Fuzz(ff interface{}) {
 		types = append(types, t)
 	}
 
-	// Check the corpus provided by f.Add
-	for _, c := range f.corpus {
-		if err := f.fuzzContext.checkCorpus(c.Values, types); err != nil {
-			// TODO: Is there a way to save which line number is associated
-			// with the f.Add call that failed?
+	// Only load the corpus if we need it
+	if f.fuzzContext.runFuzzWorker == nil {
+		// Check the corpus provided by f.Add
+		for _, c := range f.corpus {
+			if err := f.fuzzContext.checkCorpus(c.Values, types); err != nil {
+				// TODO: Is there a way to save which line number is associated
+				// with the f.Add call that failed?
+				f.Fatal(err)
+			}
+		}
+
+		// Load seed corpus
+		c, err := f.fuzzContext.readCorpus(filepath.Join(corpusDir, f.name), types)
+		if err != nil {
 			f.Fatal(err)
 		}
-	}
 
-	// Load seed corpus
-	c, err := f.fuzzContext.readCorpus(filepath.Join(corpusDir, f.name), types)
-	if err != nil {
-		f.Fatal(err)
+		// If this is the coordinator process, zero the values, since we don't need to hold
+		// onto them.
+		if f.fuzzContext.coordinateFuzzing != nil {
+			for i := range c {
+				c[i].Values = nil
+			}
+		}
+
+		f.corpus = append(f.corpus, c...)
 	}
-	f.corpus = append(f.corpus, c...)
 
 	// run calls fn on a given input, as a subtest with its own T.
 	// run is analogous to T.Run. The test filtering and cleanup works similarly.