Re: [PATCH v2 2/3] bpf: do not walk twice the hash map on free

On Apr 30 2024, Benjamin Tissoires 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

---

changes in v2:

• fix wq being not freed (and static call not used)

---

kernel/bpf/hashtab.c | 49 +++++++++++++------------------------------------ 1 file changed, 13 insertions(+), 36 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 0179183c543a..5eefadfc8ea9 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -221,32 +221,11 @@ static bool htab_has_extra_elems(struct bpf_htab *htab) return !htab_is_percpu(htab) && !htab_is_lru(htab); } -static void htab_free_prealloced_timers(struct bpf_htab *htab) +static void htab_free_prealloced_timers_and_wq(struct bpf_htab *htab) { u32 num_entries = htab->map.max_entries; int i;

• if (!btf_record_has_field(htab->map.record, BPF_TIMER))

• return;
  

• if (htab_has_extra_elems(htab))

• num_entries += num_possible_cpus();
  

• for (i = 0; i < num_entries; i++) {

• struct htab_elem *elem;
  

• elem = get_htab_elem(htab, i);
  

• bpf_obj_free_timer(htab->map.record, elem->key + round_up(htab->map.key_size, 8));
  

• cond_resched();
  

• }

-}

-static void htab_free_prealloced_wq(struct bpf_htab *htab) -{

• u32 num_entries = htab->map.max_entries;
• int i;
• if (!btf_record_has_field(htab->map.record, BPF_WORKQUEUE))

• return;
  

  if (htab_has_extra_elems(htab)) num_entries += num_possible_cpus();

@@ -254,8 +233,12 @@ static void htab_free_prealloced_wq(struct bpf_htab *htab) struct htab_elem *elem; elem = get_htab_elem(htab, i);

• bpf_obj_free_workqueue(htab->map.record,
  

• 		       elem->key + round_up(htab->map.key_size, 8));
  

• if (btf_record_has_field(htab->map.record, BPF_TIMER))
  

• 	bpf_obj_free_timer(htab->map.record,
  

• 			   elem->key + round_up(htab->map.key_size, 8));
  

• else
  

Sorry, this else above is wrong, it should be a check on BPF_WORKQUEUE instead.

v3 is n its way (with the proper bpf-next suffix this time).

Cheers, Benjamin

• 	bpf_obj_free_workqueue(htab->map.record,
  

• 			       elem->key + round_up(htab->map.key_size, 8));
  

  cond_resched(); }

} @@ -1515,7 +1498,7 @@ 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_and_wq(struct bpf_htab *htab) { int i; @@ -1527,10 +1510,10 @@ 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));
  

  }

@@ -1544,17 +1527,11 @@ 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 (!htab_is_prealloc(htab))
  

• 	htab_free_malloced_timers_or_wq(htab, true);
  

• else
  

• 	htab_free_prealloced_timers(htab);
  

• }
• if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE)) {

• if (btf_record_has_field(htab->map.record, BPF_TIMER | BPF_WORKQUEUE)) { if (!htab_is_prealloc(htab))

• 	htab_free_malloced_timers_or_wq(htab, false);
  

• 	htab_free_malloced_timers_and_wq(htab);
  

  else

• 	htab_free_prealloced_wq(htab);
  

• 	htab_free_prealloced_timers_and_wq(htab);
  

  }

}

-- 2.44.0