runtime: fix deadlock in TestCrashDumpsAllThreads

TestCrashDumpsAllThreads carefully sets the number of Ps to one
greater than the number of non-preemptible loops it starts so that the
main goroutine can continue to run (necessary because of #10958).
However, if GC starts, it can take over that one spare P and lock up
the system while waiting for the non-preemptible loops, causing the
test to eventually time out. This deadlock is easily reproducible if
you run the runtime test with GOGC=1.

Fix this by forcing GOGC=off when running this test.

Change-Id: Ifb22da5ce33f9a61700a326ea92fcf4b049721d1
Reviewed-on: https://go-review.googlesource.com/19516
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/runtime/crash_unix_test.go b/src/runtime/crash_unix_test.go
index 1a012eb6ef15c95afc9580639b29c0b7c6be7d37..771b303f6ee39aee0025469353f698d497f736c1 100644 (file)
--- a/src/runtime/crash_unix_test.go
+++ b/src/runtime/crash_unix_test.go
@@ -14,6 +14,7 @@ import (
        "os/exec"
        "path/filepath"
        "runtime"
+       "strings"
        "syscall"
        "testing"
 )
@@ -52,6 +53,18 @@ func TestCrashDumpsAllThreads(t *testing.T) {
        cmd = exec.Command(filepath.Join(dir, "a.exe"))
        cmd = testEnv(cmd)
        cmd.Env = append(cmd.Env, "GOTRACEBACK=crash")
+
+       // Set GOGC=off. Because of golang.org/issue/10958, the tight
+       // loops in the test program are not preemptible. If GC kicks
+       // in, it may lock up and prevent main from saying it's ready.
+       newEnv := []string{}
+       for _, s := range cmd.Env {
+               if !strings.HasPrefix(s, "GOGC=") {
+                       newEnv = append(newEnv, s)
+               }
+       }
+       cmd.Env = append(newEnv, "GOGC=off")
+
        var outbuf bytes.Buffer
        cmd.Stdout = &outbuf
        cmd.Stderr = &outbuf