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

On Thu, Apr 25, 2024 at 6:59 AM Benjamin Tissoires bentiss@kernel.org 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@kernel.org

---

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.

pw-bot: cr