[dpdk-dev] [PATCH v4 1/2] hash table: fix a bug in rte_hash_iterate()

[Qiaobin Fu <qiaobinf@bu.edu>]

In current implementation of rte_hash_iterate(), it
tries to obtain the lock after the while loop. However,
this may lead to a bug. Notice the following racing condition:

1. The while loop above finishes because it finds
   a not empty slot. But it does so without a lock.
2. Then we get the lock.
3. The position that was once not empty is now empty.
   BUG because next_key is invalid.

This patch fixes this small bug.

Signed-off-by: Qiaobin Fu <qiaobinf@bu.edu>
Reviewed-by: Michel Machado <michel@digirati.com.br>
---
 lib/librte_hash/rte_cuckoo_hash.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index f7b86c8c9..a3e76684d 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -1317,16 +1317,18 @@ rte_hash_iterate(const struct rte_hash *h, const void **key, void **data, uint32
 	bucket_idx = *next / RTE_HASH_BUCKET_ENTRIES;
 	idx = *next % RTE_HASH_BUCKET_ENTRIES;
 
+	__hash_rw_reader_lock(h);
 	/* If current position is empty, go to the next one */
 	while (h->buckets[bucket_idx].key_idx[idx] == EMPTY_SLOT) {
 		(*next)++;
 		/* End of table */
-		if (*next == total_entries)
+		if (*next == total_entries) {
+			__hash_rw_reader_unlock(h);
 			return -ENOENT;
+		}
 		bucket_idx = *next / RTE_HASH_BUCKET_ENTRIES;
 		idx = *next % RTE_HASH_BUCKET_ENTRIES;
 	}
-	__hash_rw_reader_lock(h);
 	/* Get position of entry in key table */
 	position = h->buckets[bucket_idx].key_idx[idx];
 	next_key = (struct rte_hash_key *) ((char *)h->key_store +
-- 
2.17.1