Do not block try lock on state mutex

TryLock should not block when file lock is held by other process and
state lock is held by other coroutine which waits for file lock.

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>

Author: koct9i

storage/pkg/lockfile/lockfile.go

@@ -420,7 +420,10 @@ func (l *LockFile) tryLock(lType rawfilelock.LockType) error {
 	if !success {
 		return fmt.Errorf("resource temporarily unavailable")
 	}
-	l.stateMutex.Lock()
+	if !l.stateMutex.TryLock() {
+		rwMutexUnlocker()
+		return fmt.Errorf("resource temporarily unavailable")
+	}
 	defer l.stateMutex.Unlock()
 	if l.counter == 0 {
 		// If we're the first reference on the lock, we need to open the file again.

storage/pkg/lockfile/lockfile_test.go

@@ -277,6 +277,55 @@ func TestTryReadLockFile(t *testing.T) {
 	assert.Nil(t, <-errChan)
 }
 
+func TestTryLockState(t *testing.T) {
+	l, err := getTempLockfile()
+	require.NoError(t, err, "creating lock")
+	defer os.Remove(l.name)
+
+	// Take a write lock somewhere.
+	cmd, wc, rc, err := subLock(l)
+	require.NoError(t, err)
+	_, err = io.Copy(io.Discard, rc)
+	require.NoError(t, err)
+
+	err = l.TryRLock()
+	assert.NotNil(t, err)
+
+	// Lock and hold state mutex.
+	locked := make(chan bool)
+	go func() {
+		locked <- false
+		l.RLock()
+		locked <- true
+		l.Unlock()
+		locked <- false
+	}()
+
+	assert.False(t, <-locked)
+
+	// Wait state mutex is locked.
+	for l.stateMutex.TryLock() {
+		l.stateMutex.Unlock()
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	// Try locks should fail without blocking.
+	errChan := make(chan error)
+	go func() {
+		errChan <- l.TryRLock()
+		errChan <- l.TryLock()
+	}()
+	assert.NotNil(t, <-errChan)
+	assert.NotNil(t, <-errChan)
+
+	wc.Close()
+	err = cmd.Wait()
+	require.NoError(t, err)
+
+	assert.True(t, <-locked)
+	assert.False(t, <-locked)
+}
+
 func TestLockfileRead(t *testing.T) {
 	l, err := getTempLockfile()
 	require.Nil(t, err, "error getting temporary lock file")