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

["Fu, Siyuan" <siyuan.fu@intel.com>]

Jiaxin, 

There will be problem if someone calls Mtftp.Start() at TPL Callback to send/receive a file with your patch. In such case the RestoreTpl() won't be able to restore the TPL to application level so it will still while loop in the Poll.

BestRegards
Fu Siyuan

> -----Original Message-----
> From: Wu, Jiaxin
> Sent: Friday, March 2, 2018 9:18 AM
> To: Fu, Siyuan <siyuan.fu@intel.com>; edk2-devel@lists.01.org
> Cc: Wang, Fan <fan.wang@intel.com>; Ye, Ting <ting.ye@intel.com>
> Subject: RE: [Patch] MdeModulePkg/Mtftp4Dxe: Restore the TPL before the
> poll function.
> 
> It's not actual hang but always running at while-poll function in the TPL
> call back level , meanwhile, the while condition depends on another time
> event that running on the same TPL. If so, the time event might have no
> chance to be triggered. So, the code will never run out of while () {}:
> 
>   while (Token->Status == EFI_NOT_READY) {
>     This->Poll (This);
>   }
> 
> 
> Thanks,
> Jiaxin
> 
> > -----Original Message-----
> > From: Fu, Siyuan
> > Sent: Thursday, March 1, 2018 7:03 PM
> > To: Wu, Jiaxin <jiaxin.wu@intel.com>; edk2-devel@lists.01.org
> > Cc: Wang, Fan <fan.wang@intel.com>; Ye, Ting <ting.ye@intel.com>
> > Subject: RE: [Patch] MdeModulePkg/Mtftp4Dxe: Restore the TPL before the
> > poll function.
> >
> > Hi, Jiaxin
> >
> > Do you mean the code which calls MTFTP4->Poll() at TPL_CALLBACK will
> > cause system hang? This should not happen because all network protocol
> > should be able to run at TPL_CALLBACK.
> >
> > BestRegards
> > Fu Siyuan
> >
> >
> > > -----Original Message-----
> > > From: Wu, Jiaxin
> > > Sent: Thursday, March 1, 2018 5:38 PM
> > > To: edk2-devel@lists.01.org
> > > Cc: Wang, Fan <fan.wang@intel.com>; Fu, Siyuan <siyuan.fu@intel.com>;
> > Ye,
> > > Ting <ting.ye@intel.com>
> > > Subject: [Patch] MdeModulePkg/Mtftp4Dxe: Restore the TPL before the
> > poll
> > > function.
> > >
> > > 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