[PATCH v3 bpf]: libbpf: fixing leak when kernel does not support btf

["Nikita V. Shirokov" <tehnerd@tehnerd.com>]

we could end up in situation when we have object file w/ all btf
info but kernel does not support btf yet. in this situation currently
libbpf just set obj->btf to NULL w/o freeing it first.
this patch if fixing it by making sure to run btf__free first

v2->v3:
 - adding "Fixes" tag

v1->v2:
 - adding netdev to cc

Fixes: 8a138aed4a80 ("bpf: btf: Add BTF support to libbpf")
Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
---
 tools/lib/bpf/libbpf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f5eb60379c8d..d5b830d60601 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -838,6 +838,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
 			if (IS_ERR(obj->btf) || btf__load(obj->btf)) {
 				pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
 					   BTF_ELF_SEC, PTR_ERR(obj->btf));
+				if (!IS_ERR(obj->btf))
+					btf__free(obj->btf);
 				obj->btf = NULL;
 			}
 		} else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
-- 
2.17.1