unity5.4 pbr shadow wrong

Code (CSharp):

1. inline half4 LightingStandardSpecular (SurfaceOutputStandardSpecular s, half3 viewDir, UnityGI gi)
2. {
3.     s.Normal = normalize(s.Normal);
4.  
5.     // energy conservation
6.     half oneMinusReflectivity=0;
7.     //s.Albedo = EnergyConservationBetweenDiffuseAndSpecular (s.Albedo, s.Specular, /*out*/ oneMinusReflectivity);
8.  
9.     // shader relies on pre-multiply alpha-blend (_SrcBlend = One, _DstBlend = OneMinusSrcAlpha)
10.     // this is necessary to handle transparency in physically correct way - only diffuse component gets affected by alpha
11.     half outputAlpha;
12.     //s.Albedo = PreMultiplyAlpha (s.Albedo, s.Alpha, 1, /*out*/ outputAlpha);
13.  
14.     half4 c = UNITY_BRDF_PBS (s.Albedo, s.Specular, oneMinusReflectivity, s.Smoothness, s.Normal, viewDir, gi.light, gi.indirect);
15.     //c.rgb += UNITY_BRDF_GI (s.Albedo, s.Specular, oneMinusReflectivity, s.Smoothness, s.Normal, viewDir, s.Occlusion, gi);
16. //    c.a = outputAlpha;
17. //c .rgb=s.Specular;
18.     return c;
19. }
20.  
21.  
22. inline void LightingStandardSpecular_GI (
23.     SurfaceOutputStandardSpecular s,
24.     UnityGIInput data,
25.     inout UnityGI gi)
26. {
27.  
28.     UNITY_GI(gi, s, data);
29.  
30. }

i not change the unity_gi,but the shadow go through two sides,how to fixed this?