libbpf: Deprecate bpf_objects_list

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: libbpf/libbpf#293 Signed-off-by: Joe Burton <[email protected]> Signed-off-by: Andrii Nakryiko <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
vieko · Oct 27, 2021 · 689624f · 689624f
1 parent 20d1b54
commit 689624f
Show file tree

Hide file tree

Showing 3 changed files with 15 additions and 2 deletions.
diff --git 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
@@ -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
@@ -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,
 };