Re: [PATCH] libbpf: Deprecate bpf_objects_list

From: Joe Burton
Date: Tue Oct 26 2021 - 18:36:28 EST


I messed up the mailing lists and will be resending this patch series
in a moment. Apologies for the noise.

Best,
Joe Burton


On Tue, Oct 26, 2021 at 3:27 PM Joe Burton <jevburton.kernel@xxxxxxxxx> wrote:
>
> From: Joe Burton <jevburton@xxxxxxxxxx>
>
> Add a flag to `enum libbpf_strict_mode' to disable the global
> `bpf_objects_list', preventing race conditions when concurrent threads
> call bpf_object__open() or bpf_object__close().
>
> bpf_object__next() will return NULL if this option is set.
>
> Callers may achieve the same workflow by tracking bpf_objects in
> application code.
>
> [0] Closes: https://github.com/libbpf/libbpf/issues/293
>
> Signed-off-by: Joe Burton <jevburton@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 8 +++++++-
> tools/lib/bpf/libbpf.h | 3 ++-
> tools/lib/bpf/libbpf_legacy.h | 6 ++++++
> 3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 2fbed2d4a645..59d39ce9f375 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1148,6 +1148,7 @@ static struct bpf_object *bpf_object__new(const char *path,
> size_t obj_buf_sz,
> const char *obj_name)
> {
> + bool strict = (libbpf_mode & LIBBPF_STRICT_NO_OBJECT_LIST);
> struct bpf_object *obj;
> char *end;
>
> @@ -1188,7 +1189,8 @@ static struct bpf_object *bpf_object__new(const char *path,
> obj->loaded = false;
>
> INIT_LIST_HEAD(&obj->list);
> - list_add(&obj->list, &bpf_objects_list);
> + if (!strict)
> + list_add(&obj->list, &bpf_objects_list);
> return obj;
> }
>
> @@ -7935,6 +7937,10 @@ struct bpf_object *
> bpf_object__next(struct bpf_object *prev)
> {
> struct bpf_object *next;
> + bool strict = (libbpf_mode & LIBBPF_STRICT_NO_OBJECT_LIST);
> +
> + if (strict)
> + return NULL;
>
> if (!prev)
> next = list_first_entry(&bpf_objects_list,
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index e1900819bfab..defabdbe7760 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -168,7 +168,8 @@ LIBBPF_API struct bpf_program *
> bpf_object__find_program_by_name(const struct bpf_object *obj,
> const char *name);
>
> -LIBBPF_API struct bpf_object *bpf_object__next(struct bpf_object *prev);
> +LIBBPF_API LIBBPF_DEPRECATED_SINCE(0, 7, "track bpf_objects in application code instead")
> +struct bpf_object *bpf_object__next(struct bpf_object *prev);
> #define bpf_object__for_each_safe(pos, tmp) \
> for ((pos) = bpf_object__next(NULL), \
> (tmp) = bpf_object__next(pos); \
> diff --git a/tools/lib/bpf/libbpf_legacy.h b/tools/lib/bpf/libbpf_legacy.h
> index 29ccafab11a8..5ba5c9beccfa 100644
> --- a/tools/lib/bpf/libbpf_legacy.h
> +++ b/tools/lib/bpf/libbpf_legacy.h
> @@ -57,6 +57,12 @@ enum libbpf_strict_mode {
> * function name instead of section name.
> */
> LIBBPF_STRICT_SEC_NAME = 0x04,
> + /*
> + * Disable the global 'bpf_objects_list'. Maintaining this list adds
> + * a race condition to bpf_object__open() and bpf_object__close().
> + * Clients can maintain it on their own if it is valuable for them.
> + */
> + LIBBPF_STRICT_NO_OBJECT_LIST = 0x08,
>
> __LIBBPF_STRICT_LAST,
> };
> --
> 2.33.0.1079.g6e70778dc9-goog
>