Re: [PATCH v1 1/3] MdeModulePkg/Dhcp4Dxe: Remove unnecessary NULL pointer check.

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

Hi, Jiaxin

> -----Original Message-----
> From: Wu, Jiaxin
> Sent: Thursday, January 17, 2019 9:01 AM
> To: edk2-devel@lists.01.org
> Cc: Ye, Ting <ting.ye@intel.com>; Fu, Siyuan <siyuan.fu@intel.com>; Wu, Hao A
> <hao.a.wu@intel.com>; Gao, Liming <liming.gao@intel.com>; Wu, Jiaxin
> <jiaxin.wu@intel.com>
> Subject: [PATCH v1 1/3] MdeModulePkg/Dhcp4Dxe: Remove unnecessary NULL pointer
> check.
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1469
> 
> Since the value of Instance is retrieved from the list Entry,
> it can't be the NULL pointer, so just remove the unnecessary
> check.
> 
> Cc: Ye Ting <ting.ye@intel.com>
> Cc: Fu Siyuan <siyuan.fu@intel.com>
> Cc: Wu Hao A <hao.a.wu@intel.com>
> Cc: Gao Liming <liming.gao@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
> ---
>  MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Io.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Io.c
> b/MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Io.c
> index 98a22a77b4..04d47e0759 100644
> --- a/MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Io.c
> +++ b/MdeModulePkg/Universal/Network/Dhcp4Dxe/Dhcp4Io.c
> @@ -1,9 +1,9 @@
>  /** @file
>    EFI DHCP protocol implementation.
> 
> -Copyright (c) 2006 - 2018, Intel Corporation. All rights reserved.<BR>
> +Copyright (c) 2006 - 2019, Intel Corporation. All rights reserved.<BR>
>  This program and the accompanying materials
>  are licensed and made available under the terms and conditions of the BSD
> License
>  which accompanies this distribution.  The full text of the license may be
> found at
>  http://opensource.org/licenses/bsd-license.php
> 
> @@ -1493,15 +1493,15 @@ DhcpOnTimerTick (
>    IN EFI_EVENT              Event,
>    IN VOID                   *Context
>    )
>  {
>    LIST_ENTRY                *Entry;
> -  LIST_ENTRY                *Next;
>    DHCP_SERVICE              *DhcpSb;
>    DHCP_PROTOCOL             *Instance;
>    EFI_STATUS                Status;
> 
> +  Entry    = NULL;
>    DhcpSb   = (DHCP_SERVICE *) Context;
>    Instance = DhcpSb->ActiveChild;
> 
>    //
>    // 0xffff is the maximum supported value for elapsed time according to RFC.
> @@ -1644,18 +1644,15 @@ DhcpOnTimerTick (
> 
>  ON_EXIT:
>    //
>    // Iterate through all the DhcpSb Children.
>    //
> -  NET_LIST_FOR_EACH_SAFE (Entry, Next, &DhcpSb->Children) {
> +  NET_LIST_FOR_EACH (Entry, &DhcpSb->Children) {

The DHCP Instance might be destroyed in PxeDhcpDone (it singals upper layer that the DHCP is completed), and the NET_LIST_FOR_EACH is not delete-safe, you should not replace it with NET_LIST_FOR_EACH.

>      Instance = NET_LIST_USER_STRUCT (Entry, DHCP_PROTOCOL, Link);
> -
> -    if ((Instance != NULL) && (Instance->Token != NULL)) {
> -      Instance->Timeout--;
> -      if (Instance->Timeout == 0) {
> -        PxeDhcpDone (Instance);
> -      }
> +    Instance->Timeout--;
> +    if (Instance->Timeout == 0) {
> +      PxeDhcpDone (Instance);
>      }
>    }
> 
>    return ;
> 
> --
> 2.17.1.windows.2