On Thu, Feb 24, 2022 at 7:38 AM Stijn Tintel <stijn@xxxxxxxxxxxxx> wrote:
>
> On 24/02/2022 12:08, Stijn Tintel wrote:
> > On 24/02/2022 01:15, Andrii Nakryiko wrote:
> >> On Tue, Feb 22, 2022 at 6:37 PM Song Liu <song@xxxxxxxxxx> wrote:
> >>> On Tue, Feb 22, 2022 at 12:51 PM Stijn Tintel <stijn@xxxxxxxxxxxxx> wrote:
> >>>> When a BPF map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY doesn't have the
> >>>> max_entries parameter set, this parameter will be set to the number of
> >>>> possible CPUs. Due to this, the map_is_reuse_compat function will return
> >>>> false, causing the following error when trying to reuse the map:
> >>>>
> >>>> libbpf: couldn't reuse pinned map at '/sys/fs/bpf/m_logging': parameter mismatch
> >>>>
> >>>> Fix this by checking against the number of possible CPUs if the
> >>>> max_entries parameter is not set in the map definition.
> >>>>
> >>>> Fixes: 57a00f41644f ("libbpf: Add auto-pinning of maps when loading BPF objects")
> >>>> Signed-off-by: Stijn Tintel <stijn@xxxxxxxxxxxxx>
> >>> Acked-by: Song Liu <songliubraving@xxxxxx>
> >>>
> >>> I think the following fix would be more future proof, but the patch
> >>> as-is is better for
> >>> stable backport? How about we add a follow up patch on top of current
> >>> patch to fix
> >>> def->max_entries once for all?
> >> Keeping special logic for PERF_EVENT_ARRAY in one place is
> >> preferrable. With this, the changes in map_is_reuse_compat() shouldn't
> >> be necessary at all. Stijn, can you please send v2 with Song's
> >> proposed changes?
> >>
> > Will do!
>
> Unfortunately that doesn't work. In bpf_object__create_maps, we call
> bpf_object__reuse_map and map_is_reuse_compat before
> bpf_object__create_map, so we check map_info.max_entries ==
> map->def.max_entries before the latter is being overwritten.
>
> So I propose to send a v2 based on my initial submission, but use __u32
> for def_max_entries instead of int, unless someone has another suggestion?
How about we move
if (def->type == BPF_MAP_TYPE_PERF_EVENT_ARRAY && !def->max_entries) {
...
}
to bpf_object__create_maps() before bpf_object__reuse_map(). And maybe add
a helper function with it?
Thanks,
Song
