Re: [PATCH bpf-next v3 08/15] bpf: Add a few bpf_cgroup_array_* helper functions

On Mon, Jul 13, 2026 at 2:57 PM Emil Tsalapatis <[email protected]> wrote:
>
> On Mon Jul 6, 2026 at 1:19 PM EDT, Amery Hung wrote:
> > From: Martin KaFai Lau <[email protected]>
> >
> > In the upcoming patch, the array can store a struct_ops map.
> > The array could have a cfi_stubs acting as a dummy instead of
> > the dummy_bpf_prog. The array logic will need to skip the cfi_stubs
> > also in order to support storing struct_ops map in the array.
> >
> > bpf_cgroup_array_length(), bpf_cgroup_array_copy_to_user(), and
> > bpf_cgroup_array_delete_safe_at() are added as a preparation work
> > to allow skipping the cfi_stubs in the upcoming patch. This patch
> > only skips the dummy_bpf_prog which is the same as the existing behavior.
> > The current bpf_prog_array_*() callers are changed to call the new
> > bpf_cgroup_array_*(). This is a no-op change.
> >
> > Unlike bpf_prog_array_copy_to_user(), bpf_cgroup_array_copy_to_user()
> > does not need a temporary buffer. The cgroup caller already holds
> > cgroup_mutex and dereferences the effective array with
> > rcu_dereference_protected(), so it does not copy to userspace
> > from an RCU read-side critical section. Details in commit 0911287ce32b.
> >
> > Another addition is the bpf_cgroup_array_free(). This prepares
> > the array to have a different rcu gp for the struct_ops use case,
> > for example, a struct_ops could have mix of sleepable ops and
> > non-sleepable ops. In this patch, bpf_cgroup_array_free() only
> > goes through the regular rcu gp. This is a no-op change also.
> >
> > bpf_prog_dummy() is also added to return the global dummy_bpf_prog.
> >
> > bpf_cgroup_array_dummy() is added to decide the sentinel based on atype.
> > It now always returns bpf_prog_dummy(). In the upcoming patch,
> > it can return a cfi_stubs if the atype belongs to a struct_ops.
> >
> > Signed-off-by: Martin KaFai Lau <[email protected]>
> > Signed-off-by: Amery Hung <[email protected]>
>
> Reviewed-by: Emil Tsalapatis <[email protected]>
>
> One style issue below.
>
> > ---
> >  include/linux/bpf.h |  1 +
> >  kernel/bpf/cgroup.c | 79 +++++++++++++++++++++++++++++++++++++++------
> >  kernel/bpf/core.c   |  5 +++
> >  3 files changed, 76 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 047ffc029666..e371a4733135 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -2561,6 +2561,7 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array,
> >                       struct bpf_prog *include_prog,
> >                       u64 bpf_cookie,
> >                       struct bpf_prog_array **new_array);
> > +struct bpf_prog *bpf_prog_dummy(void);
> >
> >  struct bpf_run_ctx {};
> >
> > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> > index 7abbe12e108f..081d81de1816 100644
> > --- a/kernel/bpf/cgroup.c
> > +++ b/kernel/bpf/cgroup.c
> > @@ -319,6 +319,67 @@ static void bpf_cgroup_link_auto_detach(struct bpf_cgroup_link *link)
> >       link->cgroup = NULL;
> >  }
> >
> > +static void bpf_cgroup_array_free(struct bpf_prog_array *array)
> > +{
> > +     if (!array || array == &bpf_empty_prog_array)
> > +             return;
> > +     kfree_rcu(array, rcu);
> > +}
> > +
> > +static void *bpf_cgroup_array_dummy(enum cgroup_bpf_attach_type atype)
> > +{
> > +     return bpf_prog_dummy();
> > +}
> > +
> > +static int bpf_cgroup_array_length(struct bpf_prog_array *array,
> > +                                enum cgroup_bpf_attach_type atype)
> > +{
> > +     struct bpf_prog_array_item *item;
> > +     int cnt = 0;
> > +
> > +     for (item = array->items; item->prog; item++)
> > +             if (item->prog != bpf_cgroup_array_dummy(atype))
> > +                     cnt++;
>
> The outer parenthesis needs braces since its body is an if-statement.

Ack. I will add the braces.

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