Re: [PATCH 2/3] bpf: do not walk twice the hash map on free

[Alexei Starovoitov]

On Thu, Apr 25, 2024 at 6:59 AM Benjamin Tissoires <bentiss@xxxxxxxxxx> wrote:
>
> If someone stores both a timer and a workqueue in a hash map, on free, we
> would walk it twice.
> Add a check in htab_free_malloced_timers_or_wq and free the timers
> and workqueues if they are present.
>
> Fixes: 246331e3f1ea ("bpf: allow struct bpf_wq to be embedded in arraymaps and hashmaps")
> Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
> ---
>  kernel/bpf/hashtab.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index 0179183c543a..20162ae741e9 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -1515,7 +1515,7 @@ static void delete_all_elements(struct bpf_htab *htab)
>         migrate_enable();
>  }
>
> -static void htab_free_malloced_timers_or_wq(struct bpf_htab *htab, bool is_timer)
> +static void htab_free_malloced_timers_or_wq(struct bpf_htab *htab)
>  {
>         int i;
>
> @@ -1527,10 +1527,10 @@ static void htab_free_malloced_timers_or_wq(struct bpf_htab *htab, bool is_timer
>
>                 hlist_nulls_for_each_entry(l, n, head, hash_node) {
>                         /* We only free timer on uref dropping to zero */
> -                       if (is_timer)
> +                       if (btf_record_has_field(htab->map.record, BPF_TIMER))
>                                 bpf_obj_free_timer(htab->map.record,
>                                                    l->key + round_up(htab->map.key_size, 8));
> -                       else
> +                       if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE))
>                                 bpf_obj_free_workqueue(htab->map.record,
>                                                        l->key + round_up(htab->map.key_size, 8));
>                 }
> @@ -1544,18 +1544,12 @@ static void htab_map_free_timers_and_wq(struct bpf_map *map)
>         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
>
>         /* We only free timer and workqueue on uref dropping to zero */
> -       if (btf_record_has_field(htab->map.record, BPF_TIMER)) {
> +       if (btf_record_has_field(htab->map.record, BPF_TIMER | BPF_WORKQUEUE)) {
>                 if (!htab_is_prealloc(htab))
> -                       htab_free_malloced_timers_or_wq(htab, true);
> +                       htab_free_malloced_timers_or_wq(htab);
>                 else
>                         htab_free_prealloced_timers(htab);
>         }
> -       if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE)) {
> -               if (!htab_is_prealloc(htab))
> -                       htab_free_malloced_timers_or_wq(htab, false);
> -               else
> -                       htab_free_prealloced_wq(htab);

This looks wrong.
htab_free_prealloced_wq() is now unused as compiler says:
./kernel/bpf/hashtab.c:243:13: warning: ‘htab_free_prealloced_wq’
defined but not used [-Wunused-function]
  243 | static void htab_free_prealloced_wq(struct bpf_htab *htab)
      |             ^~~~~~~~~~~~~~~~~~~~~~~

and prealloced maps with wq leak wq-s.

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