John Fastabend wrote:
> Martynas Pumputis wrote:
> >
> >
> > On 7/15/21 2:30 AM, John Fastabend wrote:
> > > Martynas Pumputis wrote:
> > >> If creating an outer map of a BTF-defined map-in-map fails (via
> > >> bpf_object__create_map()), then the previously created its inner map
> > >> won't be destroyed.
> > >>
> > >> Fix this by ensuring that the destroy routines are not bypassed in the
> > >> case of a failure.
> > >>
> > >> Fixes: 646f02ffdd49c ("libbpf: Add BTF-defined map-in-map support")
> > >> Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > >> Signed-off-by: Martynas Pumputis <m@xxxxxxxxx>
> > >> ---
> > >> tools/lib/bpf/libbpf.c | 5 +++--
> > >> 1 file changed, 3 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > >> index 6f5e2757bb3c..1a840e81ea0a 100644
> > >> --- a/tools/lib/bpf/libbpf.c
> > >> +++ b/tools/lib/bpf/libbpf.c
> > >> @@ -4479,6 +4479,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
> > >> {
> > >> struct bpf_create_map_attr create_attr;
> > >> struct bpf_map_def *def = &map->def;
> > >> + int ret = 0;
> > >>
> > >> memset(&create_attr, 0, sizeof(create_attr));
> > >>
> > >> @@ -4561,7 +4562,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
> > >> }
> > >>
> > >> if (map->fd < 0)
> > >> - return -errno;
> > >> + ret = -errno;
> > >>
> > >
> > > I'm trying to track this down, not being overly familiar with this bit of
> > > code.
> > >
> > > We entered bpf_object__create_map with map->inner_map potentially set and
> > > then here we are going to zfree(&map->inner_map). I'm trying to track
> > > down if this is problematic, I guess not? But seems like we could
> > > also free a map here that we didn't create from this call in the above
> > > logic.
> > >
> >
> > Keep in mind that we free the inner map anyway if the creation of the
> > outer map was successful. Also, we don't try to recreate the map if any
> > of the steps has failed. So I think it should not be problematic.
>
> Maybe not problematic, but I'm still missing a bit of detail here.
> We create an inner map then immediately destroy it? I'll need to
> reread to understand the why part.
OK understand now ;)
