bpf: add bpf_prog_add api for bulk prog refcnt

A subsystem may need to store many copies of a bpf program, each
deserving its own reference. Rather than requiring the caller to loop
one by one (with possible mid-loop failure), add a bulk bpf_prog_add
api.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/bpf.h

@@ -224,6 +224,7 @@ void bpf_register_map_type(struct bpf_map_type_list *tl);
 
 struct bpf_prog *bpf_prog_get(u32 ufd);
 struct bpf_prog *bpf_prog_get_type(u32 ufd, enum bpf_prog_type type);
+struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i);
 struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog);
 void bpf_prog_put(struct bpf_prog *prog);
 

kernel/bpf/syscall.c

@@ -670,14 +670,20 @@ static struct bpf_prog *____bpf_prog_get(struct fd f)
 	return f.file->private_data;
 }
 
-struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog)
+struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i)
 {
-	if (atomic_inc_return(&prog->aux->refcnt) > BPF_MAX_REFCNT) {
-		atomic_dec(&prog->aux->refcnt);
+	if (atomic_add_return(i, &prog->aux->refcnt) > BPF_MAX_REFCNT) {
+		atomic_sub(i, &prog->aux->refcnt);
 		return ERR_PTR(-EBUSY);
 	}
 	return prog;
 }
+EXPORT_SYMBOL_GPL(bpf_prog_add);
+
+struct bpf_prog *bpf_prog_inc(struct bpf_prog *prog)
+{
+	return bpf_prog_add(prog, 1);
+}
 
 static struct bpf_prog *__bpf_prog_get(u32 ufd, enum bpf_prog_type *type)
 {