[dpdk-dev] [PATCH v6 1/4] hash: fix race condition in iterate

Yipeng Wang yipeng1.wang at intel.com
Thu Oct 4 18:35:44 CEST 2018


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 at dpdk.org

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



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