Re: [PATCH bpf-next v5 3/8] bpf: Introduce task open coded iterator kfuncs

[Andrii Nakryiko]

On Fri, Oct 13, 2023 at 7:02 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
>
> Hello,
>
> 在 2023/10/14 05:27, Andrii Nakryiko 写道:
> > On Wed, Oct 11, 2023 at 5:09 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
> >>
> >> This patch adds kfuncs bpf_iter_task_{new,next,destroy} which allow
> >> creation and manipulation of struct bpf_iter_task in open-coded iterator
> >> style. BPF programs can use these kfuncs or through bpf_for_each macro to
> >> iterate all processes in the system.
> >>
> >> The API design keep consistent with SEC("iter/task"). bpf_iter_task_new()
> >> accepts a specific task and iterating type which allows:
> >>
> >> 1. iterating all process in the system(BPF_TASK_ITER_ALL_PROCS)
> >>
> >> 2. iterating all threads in the system(BPF_TASK_ITER_ALL_THREADS)
> >>
> >> 3. iterating all threads of a specific task(BPF_TASK_ITER_PROC_THREADS)
> >>
> >> Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
> >> ---
> >>   kernel/bpf/helpers.c                          |  3 +
> >>   kernel/bpf/task_iter.c                        | 82 +++++++++++++++++++
> >>   .../testing/selftests/bpf/bpf_experimental.h  |  5 ++
> >>   3 files changed, 90 insertions(+)
> >>
> >> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> >> index cb24c4a916df..690763751f6e 100644
> >> --- a/kernel/bpf/helpers.c
> >> +++ b/kernel/bpf/helpers.c
> >> @@ -2555,6 +2555,9 @@ BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
> >>   BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
> >>   BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)
> >>   BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
> >> +BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
> >> +BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
> >> +BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
> >>   BTF_ID_FLAGS(func, bpf_dynptr_adjust)
> >>   BTF_ID_FLAGS(func, bpf_dynptr_is_null)
> >>   BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> >> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> >> index 2cfcb4dd8a37..caeddad3d2f1 100644
> >> --- a/kernel/bpf/task_iter.c
> >> +++ b/kernel/bpf/task_iter.c
> >> @@ -856,6 +856,88 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
> >>          bpf_mem_free(&bpf_global_ma, kit->css_it);
> >>   }
> >>
> >> +struct bpf_iter_task {
> >> +       __u64 __opaque[3];
> >> +} __attribute__((aligned(8)));
> >> +
> >> +struct bpf_iter_task_kern {
> >> +       struct task_struct *task;
> >> +       struct task_struct *pos;
> >> +       unsigned int flags;
> >> +} __attribute__((aligned(8)));
> >> +
> >> +enum {
> >> +       BPF_TASK_ITER_ALL_PROCS,
> >> +       BPF_TASK_ITER_ALL_THREADS,
> >> +       BPF_TASK_ITER_PROC_THREADS
> >> +};
> >> +
> >> +__bpf_kfunc int bpf_iter_task_new(struct bpf_iter_task *it,
> >> +               struct task_struct *task, unsigned int flags)
> >> +{
> >> +       struct bpf_iter_task_kern *kit = (void *)it;
> >> +
> >> +       BUILD_BUG_ON(sizeof(struct bpf_iter_task_kern) > sizeof(struct bpf_iter_task));
> >> +       BUILD_BUG_ON(__alignof__(struct bpf_iter_task_kern) !=
> >> +                                       __alignof__(struct bpf_iter_task));
> >> +
> >> +       kit->task = kit->pos = NULL;
> >> +       switch (flags) {
> >> +       case BPF_TASK_ITER_ALL_THREADS:
> >> +       case BPF_TASK_ITER_ALL_PROCS:
> >> +       case BPF_TASK_ITER_PROC_THREADS:
> >> +               break;
> >> +       default:
> >> +               return -EINVAL;
> >> +       }
> >> +
> >> +       if (flags == BPF_TASK_ITER_PROC_THREADS)
> >> +               kit->task = task;
> >> +       else
> >> +               kit->task = &init_task;
> >> +       kit->pos = kit->task;
> >> +       kit->flags = flags;
> >> +       return 0;
> >> +}
> >> +
> >> +__bpf_kfunc struct task_struct *bpf_iter_task_next(struct bpf_iter_task *it)
> >> +{
> >> +       struct bpf_iter_task_kern *kit = (void *)it;
> >> +       struct task_struct *pos;
> >> +       unsigned int flags;
> >> +
> >> +       flags = kit->flags;
> >> +       pos = kit->pos;
> >> +
> >> +       if (!pos)
> >> +               goto out;
> >> +
> >> +       if (flags == BPF_TASK_ITER_ALL_PROCS)
> >> +               goto get_next_task;
> >> +
> >> +       kit->pos = next_thread(kit->pos);
> >> +       if (kit->pos == kit->task) {
> >> +               if (flags == BPF_TASK_ITER_PROC_THREADS) {
> >> +                       kit->pos = NULL;
> >> +                       goto out;
> >> +               }
> >> +       } else
> >> +               goto out;
> >
> > nit: this should have {} around it to match the other if branch
> >
> > but actually, why goto out instead of return pos? same above, return
> > pos instead of goto out?
> >
>
> Thanks for the review.
>
>
> IIUC, do you mean:
>

yes, goto only makes sense when there is some common clean up or error
handling logic, in this case it's a plain return result, so no point.


> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 0772545568f1..b35debf19edb 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -913,7 +913,7 @@ __bpf_kfunc struct task_struct
> *bpf_iter_task_next(struct bpf_iter_task *it)
>          pos = kit->pos;
>
>          if (!pos)
> -               goto out;
> +               return pos;
>
>          if (flags == BPF_TASK_ITER_ALL_PROCS)
>                  goto get_next_task;
> @@ -922,18 +922,22 @@ __bpf_kfunc struct task_struct
> *bpf_iter_task_next(struct bpf_iter_task *it)
>          if (kit->pos == kit->task) {
>                  if (flags == BPF_TASK_ITER_PROC_THREADS) {
>                          kit->pos = NULL;
> -                       goto out;
> +                       return pos;
>                  }
>          } else
> -               goto out;
> +               return pos;
>
> +       /*
> +        * goto get_next_task means:
> +        * case 1: flags == BPF_TASK_ITER_ALL_PROCS
> +        * case 2: kit->pos == kit->task && flags ==
> BPF_TASK_ITER_ALL_THREADS
> +        */
>   get_next_task:
>          kit->pos = next_task(kit->pos);
>          kit->task = kit->pos;
>          if (kit->pos == &init_task)
>                  kit->pos = NULL;
>
> -out:
>          return pos;
>
>
>
> BTW, do you have some comments on patch-8 ? or I should send next
> version and pass all the CI first ?
>

I didn't think too hard about changes you are proposing, but yes, CI
should be green on submission, of course

> Thanks.
>
> >
> >> +
> >> +get_next_task:
> >> +       kit->pos = next_task(kit->pos);
> >> +       kit->task = kit->pos;
> >> +       if (kit->pos == &init_task)
> >> +               kit->pos = NULL;
> >> +
> >> +out:
> >> +       return pos;
> >> +}
> >> +
> >> +__bpf_kfunc void bpf_iter_task_destroy(struct bpf_iter_task *it)
> >> +{
> >> +}
> >> +
> >>   DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
> >>
> >>   static void do_mmap_read_unlock(struct irq_work *entry)
> >> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> >> index 8b53537e0f27..1ec82997cce7 100644
> >> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> >> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> >> @@ -457,5 +457,10 @@ extern int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
> >>   extern struct task_struct *bpf_iter_css_task_next(struct bpf_iter_css_task *it) __weak __ksym;
> >>   extern void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it) __weak __ksym;
> >>
> >> +struct bpf_iter_task;
> >> +extern int bpf_iter_task_new(struct bpf_iter_task *it,
> >> +               struct task_struct *task, unsigned int flags) __weak __ksym;
> >> +extern struct task_struct *bpf_iter_task_next(struct bpf_iter_task *it) __weak __ksym;
> >> +extern void bpf_iter_task_destroy(struct bpf_iter_task *it) __weak __ksym;
> >>
> >>   #endif
> >> --
> >> 2.20.1
> >>