runtime/pprof: fix errors in pprof_test

I think the original depth-1 argument to allocDeep was correct.
Reverted that, and also the change to maxSkip in mprof.go, which was
also incorrect. I think before we were usually passing accidentally in
the loop over matched stacks when we really should usually have been
passing in the previous loop.

Change-Id: I6a6a696463e2baf045b66f418d7afbfcb49258e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/712100
Reviewed-by: Michael Matloob <[email protected]>
TryBot-Bypass: Michael Matloob <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: matloob

src/runtime/mprof.go

@@ -49,7 +49,7 @@ const (
 	// desired maximum number of frames after expansion.
 	// This should be at least as large as the largest skip value
 	// used for profiling; otherwise stacks may be truncated inconsistently
-	maxSkip = 8
+	maxSkip = 6
 
 	// maxProfStackDepth is the highest valid value for debug.profstackdepth.
 	// It's used for the bucket.stk func.

src/runtime/pprof/pprof_test.go

@@ -2549,9 +2549,6 @@ func TestProfilerStackDepth(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.profiler, func(t *testing.T) {
-			if test.profiler == "heap" {
-				testenv.SkipFlaky(t, 74029)
-			}
 			var buf bytes.Buffer
 			if err := Lookup(test.profiler).WriteTo(&buf, 0); err != nil {
 				t.Fatalf("failed to write heap profile: %v", err)
@@ -2586,6 +2583,7 @@ func TestProfilerStackDepth(t *testing.T) {
 				t.Logf("matched stack=%s", stk)
 				if len(stk) != depth {
 					t.Errorf("want stack depth = %d, got %d", depth, len(stk))
+					continue
 				}
 
 				if rootFn, wantFn := stk[depth-1], "runtime/pprof.allocDeep"; rootFn != wantFn {
@@ -2663,7 +2661,7 @@ func goroutineDeep(t *testing.T, n int) {
 // guaranteed to have exactly the desired depth with produceProfileEvents as
 // their root frame which is expected by TestProfilerStackDepth.
 func produceProfileEvents(t *testing.T, depth int) {
-	allocDeep(depth + 1)       // +1 for produceProfileEvents, **
+	allocDeep(depth - 1)       // -1 for produceProfileEvents, **
 	blockChanDeep(t, depth-2)  // -2 for produceProfileEvents, **, chanrecv1
 	blockMutexDeep(t, depth-2) // -2 for produceProfileEvents, **, Unlock
 	memSink = nil