[dpdk-dev] [PATCH v2] hash: fix unlimited cuckoo path

[Pablo de Lara]

When trying to insert a new entry, if its target bucket is full,
the alternative location (bucket) of one of the entries is checked,
to try to find an empty slot, with make_space_bucket.
This function is called every time a new bucket is checked, recursively.
To avoid having a very long insert operation (and to avoid filling up
the stack), a limit in the number of pushes is introduced.

Fixes: 48a399119619 ("hash: replace with cuckoo hash implementation")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch at intel.com>
---

Changes in v2:
- Included Fixes line

 lib/librte_hash/rte_cuckoo_hash.c | 6 +++++-
 lib/librte_hash/rte_cuckoo_hash.h | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index 3324b17..51db006 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -419,6 +419,7 @@ rte_hash_reset(struct rte_hash *h)
 static inline int
 make_space_bucket(const struct rte_hash *h, struct rte_hash_bucket *bkt)
 {
+	static unsigned int nr_pushes;
 	unsigned i, j;
 	int ret;
 	uint32_t next_bucket_idx;
@@ -455,11 +456,13 @@ make_space_bucket(const struct rte_hash *h, struct rte_hash_bucket *bkt)
 			break;
 
 	/* All entries have been pushed, so entry cannot be added */
-	if (i == RTE_HASH_BUCKET_ENTRIES)
+	if (i == RTE_HASH_BUCKET_ENTRIES || nr_pushes > RTE_HASH_MAX_PUSHES)
 		return -ENOSPC;
 
 	/* Set flag to indicate that this entry is going to be pushed */
 	bkt->flag[i] = 1;
+
+	nr_pushes++;
 	/* Need room in alternative bucket to insert the pushed entry */
 	ret = make_space_bucket(h, next_bkt[i]);
 	/*
@@ -469,6 +472,7 @@ make_space_bucket(const struct rte_hash *h, struct rte_hash_bucket *bkt)
 	 * or return error
 	 */
 	bkt->flag[i] = 0;
+	nr_pushes = 0;
 	if (ret >= 0) {
 		next_bkt[i]->sig_alt[ret] = bkt->sig_current[i];
 		next_bkt[i]->sig_current[ret] = bkt->sig_alt[i];
diff --git a/lib/librte_hash/rte_cuckoo_hash.h b/lib/librte_hash/rte_cuckoo_hash.h
index c00aafa..1b8ffed 100644
--- a/lib/librte_hash/rte_cuckoo_hash.h
+++ b/lib/librte_hash/rte_cuckoo_hash.h
@@ -140,6 +140,8 @@ enum add_key_case {
 
 #define LCORE_CACHE_SIZE		64
 
+#define RTE_HASH_MAX_PUSHES             100
+
 #define RTE_HASH_BFS_QUEUE_MAX_LEN       1000
 
 #define RTE_XABORT_CUCKOO_PATH_INVALIDED 0x4
-- 
2.7.4