Re: [PATCH] net: gro: use IS_ERR before PTR_ERR

[Guo Zhengkui]

On 2021/12/7 22:41, Alexander Lobakin wrote:
> From: Guo Zhengkui <guozhengkui@xxxxxxxx>
> Date: Tue,  7 Dec 2021 15:31:09 +0800
>
> Hi, thanks for your patch.
>
> > fix following cocci warning:
> > ./net/core/gro.c:493:5-12: ERROR: PTR_ERR applied after initialization to constant on line 441
> >
> > Signed-off-by: Guo Zhengkui <guozhengkui@xxxxxxxx>
> > ---
> >   net/core/gro.c | 8 +++++---
> >   1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/core/gro.c b/net/core/gro.c
> > index 8ec8b44596da..ee08f7b23793 100644
> > --- a/net/core/gro.c
> > +++ b/net/core/gro.c
> > @@ -490,9 +490,11 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
> >   	if (&ptype->list == head)
> >   		goto normal;
> >   
> > -	if (PTR_ERR(pp) == -EINPROGRESS) {
> > -		ret = GRO_CONSUMED;
> > -		goto ok;
> > +	if (IS_ERR(pp)) {
> > +		if (PTR_ERR(pp) == -EINPROGRESS) {
> > +			ret = GRO_CONSUMED;
> > +			goto ok;
> > +		}
> >   	}
>
> `if (PTR_ERR(ptr) == -ERRNO)` itself is correct without a check for
> IS_ERR(). The former basically is a more precise test comparing to
> the latter.

Yes, even without `IS_ERR`, it runs well.

At least, `IS_ERR` before `PTR_ERR` is a good habit. :)

Zhengkui

> Not sure if compilers can get it well, but in ideal case the first
> will be omitted from the object code at all, and so do we.
>
> In case I'm wrong and this is a correct fix, it at least shouldn't
> increase the indentation by one, these two conditions can be placed
> into one `if` statement.
>
> NAK.
>
> >   
> >   	same_flow = NAPI_GRO_CB(skb)->same_flow;
> > --
> > 2.20.1
>
> Al