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authorHerbert Xu <herbert@gondor.apana.org.au>2017-04-27 13:44:51 +0800
committerDavid S. Miller <davem@davemloft.net>2017-04-27 11:48:24 -0400
commit6d684e54690caef45cf14051ddeb7c71beeb681b (patch)
tree1544faf80a19bf2fa47d9f2a1e5f2f98dbb17545
parent4b726e81dab2cefefd2c1cb00e3074ac0eec4b15 (diff)
downloadop-kernel-dev-6d684e54690caef45cf14051ddeb7c71beeb681b.zip
op-kernel-dev-6d684e54690caef45cf14051ddeb7c71beeb681b.tar.gz
rhashtable: Cap total number of entries to 2^31
When max_size is not set or if it set to a sufficiently large value, the nelems counter can overflow. This would cause havoc with the automatic shrinking as it would then attempt to fit a huge number of entries into a tiny hash table. This patch fixes this by adding max_elems to struct rhashtable to cap the number of elements. This is set to 2^31 as nelems is not a precise count. This is sufficiently smaller than UINT_MAX that it should be safe. When max_size is set max_elems will be lowered to at most twice max_size as is the status quo. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/rhashtable.h5
-rw-r--r--lib/rhashtable.c5
2 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index ae93b65..45f8936 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -155,6 +155,7 @@ struct rhashtable_params {
* @nelems: Number of elements in table
* @key_len: Key length for hashfn
* @p: Configuration parameters
+ * @max_elems: Maximum number of elements in table
* @rhlist: True if this is an rhltable
* @run_work: Deferred worker to expand/shrink asynchronously
* @mutex: Mutex to protect current/future table swapping
@@ -165,6 +166,7 @@ struct rhashtable {
atomic_t nelems;
unsigned int key_len;
struct rhashtable_params p;
+ unsigned int max_elems;
bool rhlist;
struct work_struct run_work;
struct mutex mutex;
@@ -327,8 +329,7 @@ static inline bool rht_grow_above_100(const struct rhashtable *ht,
static inline bool rht_grow_above_max(const struct rhashtable *ht,
const struct bucket_table *tbl)
{
- return ht->p.max_size &&
- (atomic_read(&ht->nelems) / 2u) >= ht->p.max_size;
+ return atomic_read(&ht->nelems) >= ht->max_elems;
}
/* The bucket lock is selected based on the hash and protects mutations
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index f3b82e0..751630b 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -961,6 +961,11 @@ int rhashtable_init(struct rhashtable *ht,
if (params->max_size)
ht->p.max_size = rounddown_pow_of_two(params->max_size);
+ /* Cap total entries at 2^31 to avoid nelems overflow. */
+ ht->max_elems = 1u << 31;
+ if (ht->p.max_size < ht->max_elems / 2)
+ ht->max_elems = ht->p.max_size * 2;
+
ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
if (params->nelem_hint)
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