[dpdk-dev] [PATCH v7 1/4] hash: fix race condition in iterate

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

In rte_hash_iterate, the reader lock did not protect the
while loop which checks empty entry. This created a race
condition that the entry may become empty when enters
the lock, then a wrong key data value would be read out.

This commit reads out the position in the while condition,
which makes sure that the position will not be changed
to empty before entering the lock.

Fixes: f2e3001b53ec ("hash: support read/write concurrency")
Cc: stable@dpdk.org

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Reported-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
---
 lib/librte_hash/rte_cuckoo_hash.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index f7b86c8..da8ddf4 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -1318,7 +1318,7 @@ rte_hash_iterate(const struct rte_hash *h, const void **key, void **data, uint32
 	idx = *next % RTE_HASH_BUCKET_ENTRIES;
 
 	/* If current position is empty, go to the next one */
-	while (h->buckets[bucket_idx].key_idx[idx] == EMPTY_SLOT) {
+	while ((position = h->buckets[bucket_idx].key_idx[idx]) == EMPTY_SLOT) {
 		(*next)++;
 		/* End of table */
 		if (*next == total_entries)
@@ -1326,9 +1326,8 @@ 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);
-	/* 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 +
 				position * h->key_entry_size);
 	/* Return key and data */
-- 
2.7.4