[v5,2/8] hash: fix a multi-writer race condition

Message ID 1531242001-381104-3-git-send-email-yipeng1.wang@intel.com (mailing list archive)
State Accepted, archived
Series Add read-write concurrency to rte_hash library |


Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Wang, Yipeng1 July 10, 2018, 4:59 p.m. UTC
  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 beginning 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)
 			while (likely(curr_node->prev != NULL)) {
 				prev_node = curr_node->prev;
 				prev_bkt = prev_node->bkt;