From bd34e74134645b7a7109dbf0361eb1ceb1c3d1ba Mon Sep 17 00:00:00 2001 From: hagen1778 Date: Tue, 19 Sep 2017 20:28:11 +0300 Subject: [PATCH] [release-branch.go1.9] log: fix data race on log.Output There was unprotected access to Logger.flag in log.Output which could lead to data race in cases when log.SetFlags called simultaneously. For example, "hot" switching on/off debug-mode for Logger by log.SetFlags while application still writing logs. Fixes #21935 Change-Id: I36be25f23cad44cde62ed1af28a30d276400e1b8 Reviewed-on: https://go-review.googlesource.com/64710 Reviewed-by: Joe Tsai Run-TryBot: Joe Tsai TryBot-Result: Gobot Gobot Reviewed-on: https://go-review.googlesource.com/70976 Run-TryBot: Russ Cox --- src/log/log.go | 6 +----- src/log/log_test.go | 11 +++++++++++ 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/src/log/log.go b/src/log/log.go index 587904b11c..e8e0c96636 100644 --- a/src/log/log.go +++ b/src/log/log.go @@ -147,11 +147,7 @@ func (l *Logger) formatHeader(buf *[]byte, t time.Time, file string, line int) { // provided for generality, although at the moment on all pre-defined // paths it will be 2. func (l *Logger) Output(calldepth int, s string) error { - // Get time early if we need it. - var now time.Time - if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 { - now = time.Now() - } + now := time.Now() // get this early. var file string var line int l.mu.Lock() diff --git a/src/log/log_test.go b/src/log/log_test.go index 966fdf306b..adc15e7e8e 100644 --- a/src/log/log_test.go +++ b/src/log/log_test.go @@ -88,6 +88,17 @@ func TestOutput(t *testing.T) { } } +func TestOutputRace(t *testing.T) { + var b bytes.Buffer + l := New(&b, "", 0) + for i := 0; i < 100; i++ { + go func() { + l.SetFlags(0) + }() + l.Output(0, "") + } +} + func TestFlagAndPrefixSetting(t *testing.T) { var b bytes.Buffer l := New(&b, "Test:", LstdFlags)