hash: fix race condition in iterate

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
Reported-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index f7b86c8c95d1bc0799c32d2c2f3868072ef16911..da8ddf40a58c979f4c772de1001c6ff6099f6247 100644 (file)
--- 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 */