netdev - Re: [PATCH net] net/sched: act_connmark: handle errno on tcf_idr_check

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Date:   Fri, 24 Feb 2023 14:12:21 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Pedro Tammela <pctammela@...atatu.com>, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        error27@...il.com
Subject: Re: [PATCH net] net/sched: act_connmark: handle errno on
 tcf_idr_check_alloc

Hi Jamal,

On Fri, Feb 24, 2023 at 08:04:44AM -0500, Jamal Hadi Salim wrote:
> On Fri, Feb 24, 2023 at 4:05 AM Simon Horman <simon.horman@...igine.com> wrote:
> >
> 
> [..]
> 
> > Hi Pedro,
> >
> > I think the issue here isn't so much that there may be incorrect usage of
> > ci - although that can happen - but rather that an error condition - the
> > failure of tcf_idr_check_alloc is ignored.
> >
> > Viewed through this lens I think it becomes clear that the hunk
> > below fixes the problem. While the hunks above are cleanups.
> > A nice cleanup. But still a cleanup.
> >
> 
> I agree with your analysis. The initialization could be left as is and
> the else being an error condition would cover it
> (although it is one less line with Pedro's approach).
> However, on that "else" train of thought - more comment below:
> 
> > I think that as a fix for 'net' a minimal approach is best and thus
> > the patch below.
> >
> > I'd also like to comment that the usual style for kernel code is to handle
> > error cases in conditions - typically immediately after the condition
> > arises. While non-error cases follow, outside of condtions.
> >
> > F.e.
> >
> >         err = do_something(with_something);
> >         if (err) {
> >                 /* handle error */
> >                 ...
> >         }
> >
> >         /* proceed with non-error case here */
> >         ...
> >
> > In the code at hand this is complicate by there being two non-error cases,
> > and it thus being logical to treat them conditionally.
> 
> since 0190c1d452a91 unfortunately given we have the potential of 3
> possible return codes (where's before it was either 0 or 1) and it
> would help to have consistent code in the spirit of if/else if/else -
> gact is probably the best example for this.
> My opinion is we should fix all the action init()s to follow that
> pattern. There are like 3 different patterns and the danger of making
> a mistake with clever manipulation of the return code (as is done for
> example in mpls or vlan) is susceptible to breakage once someone
> submits a patch that is not properly reviewed.

I agree with that line of thought.