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Fix race condition in logging #4519

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merged 1 commit into from
Jun 19, 2017
Merged

Fix race condition in logging #4519

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1 change: 1 addition & 0 deletions CHANGELOG.asciidoc
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ https://github.com/elastic/beats/compare/v6.0.0-alpha1...master[Check the HEAD d
*Affecting all Beats*

- Don't stop with error loading the ES template if the ES output is not enabled. {pull}4436[4436]
- Fix race condition in internal logging rotator. {pull}4519[4519]

*Filebeat*

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14 changes: 14 additions & 0 deletions libbeat/logp/file_rotator.go
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Expand Up @@ -6,6 +6,7 @@ import (
"path/filepath"
"strconv"
"strings"
"sync"
)

const RotatorMaxFiles = 1024
Expand All @@ -21,6 +22,7 @@ type FileRotator struct {

current *os.File
currentSize uint64
currentLock sync.RWMutex
}

func (rotator *FileRotator) CreateDirectory() error {
Expand Down Expand Up @@ -73,16 +75,26 @@ func (rotator *FileRotator) WriteLine(line []byte) error {
}

line = append(line, '\n')

rotator.currentLock.RLock()
_, err := rotator.current.Write(line)
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Shouldn't the Write and the increment of the currentSize occur within the same lock block? Without that it seems that the currentSize may not be accurate when it is checked by other goroutines.

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Yeah you are right, I was trying to keep Write under a RLock as it may block for a while, and sacrifice some consistency in currentSize in favor of performance. Putting everything under a write lock would make goroutines logging wait on others, but yeah, this is probably overkill. What do you think?

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I'd say having currentSize slightly out of date is fine, we just use it for the rotator so it's ok if that starts a bit late.

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what do you think @andrewkroh? I can also add some comment explaining this

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I'm OK with the behavior as is.

rotator.currentLock.RUnlock()

if err != nil {
return err
}

rotator.currentLock.Lock()
rotator.currentSize += uint64(len(line))
rotator.currentLock.Unlock()

return nil
}

func (rotator *FileRotator) shouldRotate() bool {
rotator.currentLock.RLock()
defer rotator.currentLock.RUnlock()

if rotator.current == nil {
return true
}
Expand Down Expand Up @@ -112,6 +124,8 @@ func (rotator *FileRotator) FileExists(fileNo int) bool {
}

func (rotator *FileRotator) Rotate() error {
rotator.currentLock.Lock()
defer rotator.currentLock.Unlock()

if rotator.current != nil {
if err := rotator.current.Close(); err != nil {
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29 changes: 29 additions & 0 deletions libbeat/logp/file_rotator_test.go
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Expand Up @@ -174,3 +174,32 @@ func TestConfigSane(t *testing.T) {
}
assert.NotNil(t, rotator.CheckIfConfigSane())
}

func TestRaceConditions(t *testing.T) {
// Make sure concurrent `WriteLine` calls don't end up in race conditions around `rotator.current`
if testing.Verbose() {
LogInit(LOG_DEBUG, "", false, true, []string{"rotator"})
}

dir, err := ioutil.TempDir("", "test_rotator_")
if err != nil {
t.Errorf("Error: %s", err.Error())
return
}

Debug("rotator", "Directory: %s", dir)

rotateeverybytes := uint64(10)
keepfiles := 20

rotator := FileRotator{
Path: dir,
Name: "testbeat",
RotateEveryBytes: &rotateeverybytes,
KeepFiles: &keepfiles,
}

for i := 0; i < 1000; i++ {
go rotator.WriteLine([]byte(string(i)))
}
}