[dpdk-dev] [PATCH v4 2/8] hash: fix a multi-writer race condition

[Yipeng Wang <yipeng1.wang@intel.com>]

Current multi-writer implementation uses Intel TSX to
protect the cuckoo path moving but not the cuckoo
path searching. After searching, we need to verify again if
the same empty slot still exists at the begining of the TSX
region. Otherwise another writer could occupy the empty slot
before the TSX region. Current code does not verify.

Fixes: be856325cba3 ("hash: add scalable multi-writer insertion with Intel TSX")
Cc: stable@dpdk.org

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
---
 lib/librte_hash/rte_cuckoo_hash_x86.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/librte_hash/rte_cuckoo_hash_x86.h b/lib/librte_hash/rte_cuckoo_hash_x86.h
index 2c5b017..981d7bd 100644
--- a/lib/librte_hash/rte_cuckoo_hash_x86.h
+++ b/lib/librte_hash/rte_cuckoo_hash_x86.h
@@ -66,6 +66,9 @@ rte_hash_cuckoo_move_insert_mw_tm(const struct rte_hash *h,
 	while (try < RTE_HASH_TSX_MAX_RETRY) {
 		status = rte_xbegin();
 		if (likely(status == RTE_XBEGIN_STARTED)) {
+			/* In case empty slot was gone before entering TSX */
+			if (curr_bkt->key_idx[curr_slot] != EMPTY_SLOT)
+				rte_xabort(RTE_XABORT_CUCKOO_PATH_INVALIDED);
 			while (likely(curr_node->prev != NULL)) {
 				prev_node = curr_node->prev;
 				prev_bkt = prev_node->bkt;
-- 
2.7.4