2021-10-27 12:31:07

by Joe Burton

Subject: [PATCH v2] libbpf: Deprecate bpf_objects_list

From: Joe Burton <[email protected]>

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 <[email protected]>
---
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

2021-10-27 21:34:38

by Andrii Nakryiko

Subject: Re: [PATCH v2] libbpf: Deprecate bpf_objects_list

On Tue, Oct 26, 2021 at 3:35 PM Joe Burton <[email protected]> wrote:
>
> From: Joe Burton <[email protected]>
>
> 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 <[email protected]>
> ---

Applied to bpf-next, thanks. Please specify kernel tree next time
(i.e., [PATCH bpf-next] subject prefix)


> 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(-)
>

[...]