[PATCH bpf-next v3 2/3] bpf: do not walk twice the hash map on free

Benjamin Tissoires
2024-04-30T10:43:40Z

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 v3:
- fix unloading of bpf_wq, again

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..06115f8728e8 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -221,13 +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();

@@ -235,27 +233,12 @@ static void htab_free_prealloced_timers(struct bpf_htab *htab)
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();
-
- for (i = 0; i < num_entries; i++) {
- 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));
+ if (btf_record_has_field(htab->map.record, BPF_WORKQUEUE))
+ 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