Re: [PATCH bpf-next v3 2/5] bpf: implement sleepable uprobes by chaining gps

[Delyan Kratunov <delyank@fb.com>]

On Fri, 2022-05-13 at 18:00 +0200, Daniel Borkmann wrote:
> On 5/13/22 3:22 AM, Delyan Kratunov wrote:
> [...]
> >   struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags);
> >   void bpf_prog_array_free(struct bpf_prog_array *progs);
> > +/* Use when traversal over the bpf_prog_array uses tasks_trace rcu */
> > +void bpf_prog_array_free_sleepable(struct bpf_prog_array *progs);
> >   int bpf_prog_array_length(struct bpf_prog_array *progs);
> >   bool bpf_prog_array_is_empty(struct bpf_prog_array *array);
> >   int bpf_prog_array_copy_to_user(struct bpf_prog_array *progs,
> > @@ -1451,6 +1454,56 @@ bpf_prog_run_array(const struct bpf_prog_array *array,
> >   	return ret;
> >   }
> >   
> > +/**
> > + * Notes on RCU design for bpf_prog_arrays containing sleepable programs:
> > + *
> > + * We use the tasks_trace rcu flavor read section to protect the bpf_prog_array
> > + * overall. As a result, we must use the bpf_prog_array_free_sleepable
> > + * in order to use the tasks_trace rcu grace period.
> > + *
> > + * When a non-sleepable program is inside the array, we take the rcu read
> > + * section and disable preemption for that program alone, so it can access
> > + * rcu-protected dynamically sized maps.
> > + */
> 
> Btw, there are a number of kdoc warnings around your series, pls make sure to
> fix or use 'regular' comment:
> 
> https://patchwork.hopto.org/static/nipa/641204/12848281/kdoc/stderr 
> https://patchwork.hopto.org/static/nipa/641204/12848282/kdoc/stderr 

Yeah, I just saw these too, I'll take care of them before the next reroll. Let's see
if there's any other high level comments first.

-- Delyan