[v4,1/2] hash table: fix a bug in rte_hash_iterate()
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Commit Message
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(-)
Comments
Hi Qiaobin,
This patch: http://patchwork.dpdk.org/patch/46105/ covers the bug. Honnappa suggested a fix that would work well for the lock free implementation as well.
>-----Original Message-----
>From: Qiaobin Fu [mailto:qiaobinf@bu.edu]
>Sent: Tuesday, October 9, 2018 12:29 PM
>To: Richardson, Bruce <bruce.richardson@intel.com>; De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>
>Cc: dev@dpdk.org; doucette@bu.edu; Wiles, Keith <keith.wiles@intel.com>; Gobriel, Sameh <sameh.gobriel@intel.com>; Tai, Charlie
><charlie.tai@intel.com>; stephen@networkplumber.org; nd@arm.com; honnappa.nagarahalli@arm.com; Wang, Yipeng1
><yipeng1.wang@intel.com>; michel@digirati.com.br; qiaobinf@bu.edu
>Subject: [PATCH v4 1/2] hash table: fix a bug in rte_hash_iterate()
>
>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
@@ -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 +