Re: [PATCH bpf-next] bpf: Fix a typo in comment for DFS algorithm

[Xu Kuohai]

On 10/26/2022 2:32 PM, Alexei Starovoitov wrote:
> On Tue, Oct 25, 2022 at 7:42 PM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:
> > From: Xu Kuohai <xukuohai@xxxxxxxxxx>
> >
> > There is a typo in comment for DFS algorithm in bpf/verifier.c. The top
> > element should not be popped until all its neighbors have been checked.
> > Fix it.
> >
> > Fixes: 475fb78fbf48 ("bpf: verifier (add branch/goto checks)")
> > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
> > ---
> >   kernel/bpf/verifier.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index b83a8d420520..96ba5ea6d1a6 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -10662,7 +10662,7 @@ static int check_return_code(struct bpf_verifier_env *env)
> >    * 3      let S be a stack
> >    * 4      S.push(v)
> >    * 5      while S is not empty
> > - * 6            t <- S.pop()
> > + * 6            t <- S.top()
>
> Even with this fix the comment is not quite accurate.
> I wonder whether we should keep it or delete it completely.

The comment describes the non-recursive DFS algorithm used by the C code.
Although it does not describe the full details, it helps us to understand
the code, so I think it should be kept.

> At least please use 'peek' instead of 'top'.

OK.