[Patch] MdeModulePkg/Mtftp4Dxe: Restore the TPL before the poll function.

[Jiaxin Wu <jiaxin.wu@intel.com>]

This patch is to fix the hang issue, which was enrolled by the commit of 39b0867d.
The TPL should be restored before calling poll function at TPL_CALLBACK.

Cc: Wang Fan <fan.wang@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
---
 MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c b/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
index f5f9e6d8f7..64e0463dd9 100644
--- a/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
+++ b/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
@@ -507,24 +507,27 @@ Mtftp4Start (
   if (EFI_ERROR (Status)) {
     Status = EFI_DEVICE_ERROR;
     goto ON_ERROR;
   }
 
+  //
+  // Restore the TPL now, don't call poll function at TPL_CALLBACK.
+  //
+  gBS->RestoreTPL (OldTpl);
+
   if (Token->Event != NULL) {
-    gBS->RestoreTPL (OldTpl);
     return EFI_SUCCESS;
   }
 
   //
   // Return immediately for asynchronous operation or poll the
   // instance for synchronous operation.
   //
   while (Token->Status == EFI_NOT_READY) {
     This->Poll (This);
   }
-
-  gBS->RestoreTPL (OldTpl);
+  
   return Token->Status;
 
 ON_ERROR:
   Mtftp4CleanOperation (Instance, Status);
   gBS->RestoreTPL (OldTpl);
-- 
2.16.2.windows.1