runtime: call runtime.GC in several tests that disable GC

These tests disable GC because of the potential for a deadlock, but
don't consider that a GC could be in progress due to other tests. The
likelihood of this case was increased when the minimum heap size was
lowered during the Go 1.18 cycle. The issue was then mitigated by
CL 368137 but in theory is always a problem.

This change is intended specifically for #45867, but I just walked over
a whole bunch of other tests that don't take this precaution where it
seems like it could be relevant (some tests it's not, like the
UserForcedGC test, or testprogs where no other code has run before it).

Fixes #45867.

Change-Id: I6a1b4ae73e05cab5a0b2d2cce14126bd13be0ba5
Reviewed-on: https://go-review.googlesource.com/c/go/+/369747
Reviewed-by: Michael Pratt <[email protected]>
Reviewed-by: David Chase <[email protected]>
Trust: Michael Knyszek <[email protected]>
Run-TryBot: Michael Knyszek <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: mknyszek

src/runtime/proc_test.go

@@ -119,6 +119,9 @@ func TestGoroutineParallelism(t *testing.T) {
 	// since the goroutines can't be stopped/preempted.
 	// Disable GC for this test (see issue #10958).
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	// Now that GCs are disabled, block until any outstanding GCs
+	// are also done.
+	runtime.GC()
 	for try := 0; try < N; try++ {
 		done := make(chan bool)
 		x := uint32(0)
@@ -163,6 +166,9 @@ func testGoroutineParallelism2(t *testing.T, load, netpoll bool) {
 	// since the goroutines can't be stopped/preempted.
 	// Disable GC for this test (see issue #10958).
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	// Now that GCs are disabled, block until any outstanding GCs
+	// are also done.
+	runtime.GC()
 	for try := 0; try < N; try++ {
 		if load {
 			// Create P goroutines and wait until they all run.
@@ -623,6 +629,9 @@ func TestSchedLocalQueueEmpty(t *testing.T) {
 	// If runtime triggers a forced GC during this test then it will deadlock,
 	// since the goroutines can't be stopped/preempted during spin wait.
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	// Now that GCs are disabled, block until any outstanding GCs
+	// are also done.
+	runtime.GC()
 
 	iters := int(1e5)
 	if testing.Short() {

src/runtime/testdata/testprog/badtraceback.go

@@ -17,6 +17,9 @@ func init() {
 func BadTraceback() {
 	// Disable GC to prevent traceback at unexpected time.
 	debug.SetGCPercent(-1)
+	// Out of an abundance of caution, also make sure that there are
+	// no GCs actively in progress.
+	runtime.GC()
 
 	// Run badLR1 on its own stack to minimize the stack size and
 	// exercise the stack bounds logic in the hex dump.

src/runtime/testdata/testprog/preempt.go

@@ -20,6 +20,9 @@ func AsyncPreempt() {
 	runtime.GOMAXPROCS(1)
 	// Disable GC so we have complete control of what we're testing.
 	debug.SetGCPercent(-1)
+	// Out of an abundance of caution, also make sure that there are
+	// no GCs actively in progress.
+	runtime.GC()
 
 	// Start a goroutine with no sync safe-points.
 	var ready, ready2 uint32