net: core/dev: fix sparse warning

From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>

this patch fixes following sparse warning:
net/core/dev.c: In function 'validate_xmit_skb_list':
net/core/dev.c:2720: warning: 'tail' may be used uninitialized in this function

Although its a false positive, as head is assigned to NULL in the
beginning, due which later in the loop tail is assigned to skb->prev.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Wed, 2015-02-04 at 12:25 +0000, Lad Prabhakar wrote:
> From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
> 
> this patch fixes following sparse warning:
> net/core/dev.c: In function 'validate_xmit_skb_list':
> net/core/dev.c:2720: warning: 'tail' may be used uninitialized in this function
> 
> Although its a false positive, as head is assigned to NULL in the
> beginning, due which later in the loop tail is assigned to skb->prev.
> 
> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 8ce0d1a..c736467 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2717,7 +2717,7 @@ out_null:
>  
>  struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *dev)
>  {
> -	struct sk_buff *next, *head = NULL, *tail;
> +	struct sk_buff *next, *head = NULL, *tail = NULL;
>  
>  	for (; skb != NULL; skb = next) {
>  		next = skb->next;

Which gcc/sparse versions are you using ?

I do not see this warning here.

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
4.8.2-19ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib
--enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--enable-gnu-unique-object --disable-libmudflap --enable-plugin
--with-system-zlib --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre
--enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64
--with-arch-directory=amd64
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) 

$ sparse --version
0.4.5-rc1
 


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On Wed, Feb 4, 2015 at 12:41 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Wed, 2015-02-04 at 12:25 +0000, Lad Prabhakar wrote:
>> From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
>>
>> this patch fixes following sparse warning:
>> net/core/dev.c: In function 'validate_xmit_skb_list':
>> net/core/dev.c:2720: warning: 'tail' may be used uninitialized in this function
>>
>> Although its a false positive, as head is assigned to NULL in the
>> beginning, due which later in the loop tail is assigned to skb->prev.
>>
>> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
>> ---
>>  net/core/dev.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 8ce0d1a..c736467 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2717,7 +2717,7 @@ out_null:
>>
>>  struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *dev)
>>  {
>> -     struct sk_buff *next, *head = NULL, *tail;
>> +     struct sk_buff *next, *head = NULL, *tail = NULL;
>>
>>       for (; skb != NULL; skb = next) {
>>               next = skb->next;
>
> Which gcc/sparse versions are you using ?
>
I tried it on gcc 4.3.3 and sparse with 0.4.5-rc1 version.

Regards,
--Prabhakar Lad
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On Wed, 2015-02-04 at 12:50 +0000, Lad, Prabhakar wrote:

> I tried it on gcc 4.3.3 and sparse with 0.4.5-rc1 version.

gcc-4.3.3 is 6 years old...


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