Re: [PATCH v2 bpf-next 3/7] bpf: Add per-program recursion prevention mechanism

[Alexei Starovoitov <ast@xxxxxx>]

On 2/8/21 12:51 PM, Andrii Nakryiko wrote:
> >                  start = sched_clock();
> > +               if (unlikely(!start))
> > +                       start = NO_START_TIME;
> > +       }
> >          return start;
>
>
> Oh, and actually, given you have `start > NO_START_TIME` condition in
> exit function, you don't need this `if (unlikely(!start))` bit at all,
> because you are going to ignore both 0 and 1. So maybe no need for a
> new function, but no need for extra if as well.

This unlikely(!start) is needed for very unlikely case when
sched_clock() returns 0. In such case the prog should still be executed.