RE: [PATCH dpdk v3 0/2] hash: safe data replacement on overwrite

Konstantin Ananyev
2026-03-09T07:50:19Z

> When rte_hash_add_key_data() is called with an existing key, the old
> data pointer is silently overwritten. With RCU-protected readers still
> potentially accessing the old data, the application cannot safely free
> it since the old pointer is never returned.
>
> This series fixes the issue in two places:
>
> * When RCU is configured with a free_key_data_func callback,
> rte_hash_add_key_data() now automatically defers freeing the old data
> on overwrite. No caller changes are needed.
>
> * If rte_hash_del_key() fails to enqueue the deleted entry in
> RTE_HASH_QSBR_MODE_DQ, it falls back on RTE_HASH_QSBR_MODE_SYNC to
> avoid leaking slots and data pointers.
>
> v3:
>
> * Use rte_atomic_exchange_explicit() to swap the new data pointer with
> the old one in search_and_update().
>
> * Removed the rte_hash_replace_key_data() API

That's a pity - I think it is a useful one.

> which required to bubble
> a potential old_data pointer from search_and_update() to all
> intermediate callers down to __rte_hash_add_key_with_hash(). It made
> an already complex code even more obscure.
>
> v2:
>
> * New patch to fallback to SYNC mode when DQ fails on delete.
> * Check key_idx == EMPTY_SLOT in DQ mode to differentiate when old_data
> is NULL.
> * Also fallback to SYNC mode when DQ fails on replace.
>
> Robin Jarry (2):
> hash: avoid leaking entries on RCU defer queue failure
> hash: free replaced data on overwrite when RCU is configured
>
> app/test/test_hash.c | 134 +++++++++++++++++++++++++
> doc/guides/rel_notes/release_26_03.rst | 7 ++
> lib/hash/rte_cuckoo_hash.c | 47 +++++++--
> lib/hash/rte_hash.h | 8 +-
> 4 files changed, 187 insertions(+), 9 deletions(-)
>
> --
> 2.53.0
>