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| author | Herbert Xu <herbert@gondor.apana.org.au> | 2017-04-27 07:44:51 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-04-27 17:48:24 +0200 |
| commit | 6d684e54690caef45cf14051ddeb7c71beeb681b (patch) | |
| tree | 1544faf80a19bf2fa47d9f2a1e5f2f98dbb17545 | |
| parent | tcp: tcp_rack_reo_timeout() must update tp->tcp_mstamp (diff) | |
| download | linux-6d684e54690caef45cf14051ddeb7c71beeb681b.tar.xz linux-6d684e54690caef45cf14051ddeb7c71beeb681b.zip | |
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.h | 5 | ||||
| -rw-r--r-- | lib/rhashtable.c | 5 |
2 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h index ae93b65d13d7..45f89369c4c8 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 f3b82e0d417b..751630bbe409 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) |