klog.Fatal: revert dumping of all stack backtraces to stderr

This is a revert of kubernetes#79.

Dumping the stack backtraces of all goroutines to stderr is not useful for
processes which have many goroutines. The console buffer overflows and the
original error which got dumped earlier is no longer visible. Even in CI
systems where stderr is captured the full dump is often not useful.

This was pointed out as a potential problem during the original PR review but
only got more attention after the updated klog got merged into Kubernetes and
developers there started to see the longer output.

integration_tests/klog_test.go

@@ -91,9 +91,10 @@ func TestDestinationsWithDifferentFlags(t *testing.T) {
 		notExpectedInDir map[int]res
 	}{
 		"default flags": {
-			// Everything, including the trace on fatal, goes to stderr
+			// Everything, EXCEPT the trace on fatal, goes to stderr
 
-			expectedOnStderr: allLogREs,
+			expectedOnStderr:    res{infoLogRE, warningLogRE, errorLogRE, fatalLogRE},
+			notExpectedOnStderr: res{stackTraceRE},
 		},
 		"everything disabled": {
 			// Nothing, including the trace on fatal, is showing anywhere
@@ -112,11 +113,12 @@ func TestDestinationsWithDifferentFlags(t *testing.T) {
 			notExpectedOnStderr: res{infoLogRE},
 		},
 		"with logtostderr only": {
-			// Everything, including the trace on fatal, goes to stderr
+			// Everything, EXCEPT the trace on fatal, goes to stderr
 
 			flags: []string{"-logtostderr=true", "-alsologtostderr=false", "-stderrthreshold=1000"},
 
-			expectedOnStderr: allLogREs,
+			expectedOnStderr:    res{infoLogRE, warningLogRE, errorLogRE, fatalLogRE},
+			notExpectedOnStderr: res{stackTraceRE},
 		},
 		"with log file only": {
 			// Everything, including the trace on fatal, goes to the single log file
@@ -154,13 +156,14 @@ func TestDestinationsWithDifferentFlags(t *testing.T) {
 			notExpectedInDir:    defaultNotExpectedInDirREs,
 		},
 		"with log dir and logtostderr": {
-			// Everything, including the trace on fatal, goes to stderr. The -log_dir is
+			// Everything, EXCEPT the trace on fatal, goes to stderr. The -log_dir is
 			// ignored, nothing goes to the log files in the log dir.
 
 			logdir: true,
 			flags:  []string{"-logtostderr=true", "-alsologtostderr=false", "-stderrthreshold=1000"},
 
-			expectedOnStderr: allLogREs,
+			expectedOnStderr:    res{infoLogRE, warningLogRE, errorLogRE, fatalLogRE},
+			notExpectedOnStderr: res{stackTraceRE},
 		},
 		"with log file and log dir": {
 			// Everything, including the trace on fatal, goes to the single log file.

klog.go

@@ -924,12 +924,15 @@ func (l *loggingT) output(s severity.Severity, log *logr.Logger, buf *buffer.Buf
 			OsExit(1)
 		}
 		// Dump all goroutine stacks before exiting.
-		trace := stacks(true)
-		// Write the stack trace for all goroutines to the stderr.
-		if l.toStderr || l.alsoToStderr || s >= l.stderrThreshold.get() || alsoToStderr {
-			os.Stderr.Write(trace)
+		// First, make sure we see the trace for the current goroutine on standard error.
+		// If -logtostderr has been specified, the loop below will do that anyway
+		// as the first stack in the full dump.
+		if !l.toStderr {
+			os.Stderr.Write(stacks(false))
 		}
+
 		// Write the stack trace for all goroutines to the files.
+		trace := stacks(true)
 		logExitFunc = func(error) {} // If we get a write error, we'll still exit below.
 		for log := severity.FatalLog; log >= severity.InfoLog; log-- {
 			if f := l.file[log]; f != nil { // Can be nil if -logtostderr is set.