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

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

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

I presume otherwise kbuild bot will yell at some point.

Thanks,
Daniel