On Wed, Sep 8, 2021 at 8:35 AM Hengqi Chen <hengqi.chen@xxxxxxxxx> wrote: > > BPF objects are not re-loadable after unload. User are expected to use > bpf_object__close() to unload and free up resources in one operation. > No need to expose bpf_object__unload() as a public API, deprecate it.[0] > Remove bpf_object__unload() inside bpf_object__load_xattr(), it is the > caller's responsibility to free up resources, otherwise, the following > code path will cause double-free problem when loading failed: > > bpf_prog_load > bpf_prog_load_xattr > bpf_object__load > bpf_object__load_xattr > Did you see this double-free ever happen? I'm looking at the code and not seeing it. Seems like bpf_object__unload() is idempotent, so no mater how many times we call it, it doesn't do any harm. Look at how zclose and zfree are implemented, they zero-out fields and also check for non-zero values before doing something. So unless I'm missing something, there is no problem. > Replace bpf_object__unload() inside bpf_object__close() with the necessary > cleanup operations to avoid compilation error. > > [0] Closes: https://github.com/libbpf/libbpf/issues/290 > > Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 8 +++++--- > tools/lib/bpf/libbpf.h | 3 ++- > 2 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 8f579c6666b2..c56b466c5461 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -6931,7 +6931,6 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) > if (obj->maps[i].pinned && !obj->maps[i].reused) > bpf_map__unpin(&obj->maps[i], NULL); > > - bpf_object__unload(obj); I think unloading already loaded bpf programs is bpf_object__load()'s responsibility, so please don't remove this. > pr_warn("failed to load object '%s'\n", obj->path); > return libbpf_err(err); > } > @@ -7540,12 +7539,15 @@ void bpf_object__close(struct bpf_object *obj) > > bpf_gen__free(obj->gen_loader); > bpf_object__elf_finish(obj); > - bpf_object__unload(obj); same, this is fine, don't remove it > btf__free(obj->btf); > btf_ext__free(obj->btf_ext); > > - for (i = 0; i < obj->nr_maps; i++) > + for (i = 0; i < obj->nr_maps; i++) { > + zclose(obj->maps[i].fd); > + if (obj->maps[i].st_ops) > + zfree(&obj->maps[i].st_ops->kern_vdata); > bpf_map__destroy(&obj->maps[i]); > + } and no changes should be necessary here either > > zfree(&obj->btf_custom_path); > zfree(&obj->kconfig); > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > index 2f6f0e15d1e7..748f7dabe4c7 100644 > --- a/tools/lib/bpf/libbpf.h > +++ b/tools/lib/bpf/libbpf.h > @@ -147,7 +147,8 @@ struct bpf_object_load_attr { > /* Load/unload object into/from kernel */ > LIBBPF_API int bpf_object__load(struct bpf_object *obj); > LIBBPF_API int bpf_object__load_xattr(struct bpf_object_load_attr *attr); > -LIBBPF_API int bpf_object__unload(struct bpf_object *obj); > +LIBBPF_API LIBBPF_DEPRECATED("bpf_object__unload() is deprecated, use bpf_object__close() instead") > +int bpf_object__unload(struct bpf_object *obj); > This is the right change, but let's also keep original bpf_object__unload() logic. I'd recommend renaming bpf_object__unload() into bpf_object_unload() (so that's naming is more clearly showing it's an internal function) and make it static. Then have a small shim of bpf_object__unload() calling into bpf_object_unload() until we remove that in libbpf 1.0. > LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj); > LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj); > -- > 2.25.1 >
