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Commit 6d684e54 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
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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: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4b726e81

include/linux/rhashtable.h

+3 −2
Original line number Diff line number Diff line
@@ -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

lib/rhashtable.c

+5 −0
Original line number Diff line number Diff line
@@ -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)