On 9/9/21 12:38 PM, Andrii Nakryiko wrote: > 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. > > Sorry, I made a stupid mistake. Did not realize zclose/zfree are implemented as macros. Will remove these changes. >> 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 > OK. >> 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 > Acked. >> >> 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. > OK, since LIBBPF_DEPRECATED_SINCE is landed, will use it instead. >> 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 >>
