From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: rhashtable: Move hash_rnd into bucket_table Date: Mon, 09 Mar 2015 17:26:52 +0100 Message-ID: <54FDC9CC.6080709@iogearbox.net> References: <20150131102150.GA29498@gondor.apana.org.au> <20150202.191956.404010205495035337.davem@davemloft.net> <20150202.192634.1792206005008667377.davem@davemloft.net> <20150203201750.GA22474@gondor.apana.org.au> <20150309095833.GA4028@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: tgraf@suug.ch, netdev@vger.kernel.org To: Herbert Xu , David Miller Return-path: Received: from www62.your-server.de ([213.133.104.62]:46828 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932416AbbCIQ1C (ORCPT ); Mon, 9 Mar 2015 12:27:02 -0400 In-Reply-To: <20150309095833.GA4028@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: On 03/09/2015 10:58 AM, Herbert Xu wrote: > Currently hash_rnd is a parameter that users can set. However, > no existing users set this parameter. It is also something that > people are unlikely to want to set directly since it's just a > random number. I believe the original purpose was to have reproduceability, but yeah, there are no users of it currently. > In preparation for allowing the reseeding/rehashing of rhashtable, > this patch moves hash_rnd into bucket_table so that it's now an > internal state rather than a parameter. > > Signed-off-by: Herbert Xu > > diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h > index d438eeb..5ef8ea5 100644 > --- a/include/linux/rhashtable.h > +++ b/include/linux/rhashtable.h > @@ -49,12 +49,14 @@ struct rhash_head { > /** > * struct bucket_table - Table of hash buckets > * @size: Number of hash buckets > + * @hash_rnd: Random seed to fold into hash > * @locks_mask: Mask to apply before accessing locks[] > * @locks: Array of spinlocks protecting individual buckets > * @buckets: size * hash buckets > */ > struct bucket_table { > size_t size; > + u32 hash_rnd; > unsigned int locks_mask; > spinlock_t *locks; > > @@ -72,7 +74,6 @@ struct rhashtable; > * @key_len: Length of key > * @key_offset: Offset of key in struct to be hashed > * @head_offset: Offset of rhash_head in struct to be hashed > - * @hash_rnd: Seed to use while hashing > * @max_shift: Maximum number of shifts while expanding > * @min_shift: Minimum number of shifts while shrinking > * @nulls_base: Base value to generate nulls marker > @@ -85,7 +86,6 @@ struct rhashtable_params { > size_t key_len; > size_t key_offset; > size_t head_offset; > - u32 hash_rnd; > size_t max_shift; > size_t min_shift; > u32 nulls_base; > diff --git a/lib/rhashtable.c b/lib/rhashtable.c > index b5344ef..4ce267f 100644 > --- a/lib/rhashtable.c > +++ b/lib/rhashtable.c > @@ -66,25 +66,28 @@ static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash) > return hash & (tbl->size - 1); > } > > -static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr) > +static u32 obj_raw_hashfn(struct rhashtable *ht, const void *ptr) > { > + struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); const > u32 hash; > > if (unlikely(!ht->p.key_len)) > - hash = ht->p.obj_hashfn(ptr, ht->p.hash_rnd); > + hash = ht->p.obj_hashfn(ptr, tbl->hash_rnd); > else > hash = ht->p.hashfn(ptr + ht->p.key_offset, ht->p.key_len, > - ht->p.hash_rnd); > + tbl->hash_rnd); > > return hash >> HASH_RESERVED_SPACE; > } > > static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len) > { > - return ht->p.hashfn(key, len, ht->p.hash_rnd) >> HASH_RESERVED_SPACE; > + struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht); > + const > + return ht->p.hashfn(key, len, tbl->hash_rnd) >> HASH_RESERVED_SPACE; > } > > -static u32 head_hashfn(const struct rhashtable *ht, > +static u32 head_hashfn(struct rhashtable *ht, > const struct bucket_table *tbl, > const struct rhash_head *he) > { > @@ -92,7 +95,7 @@ static u32 head_hashfn(const struct rhashtable *ht, > } > > #ifdef CONFIG_PROVE_LOCKING > -static void debug_dump_buckets(const struct rhashtable *ht, > +static void debug_dump_buckets(struct rhashtable *ht, > const struct bucket_table *tbl) > { > struct rhash_head *he; > @@ -1099,14 +1102,13 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params) > if (tbl == NULL) > return -ENOMEM; > > + get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd)); > + Have you tested this patch? ;-) If I see this correctly, the first time you shrink or expand, your hash_rnd from then onwards will constantly be 0. You need to copy over the above old hash_rnd to the new one from the newly allocated tbl. So, bucket_table_alloc() needs a change as well. Of course, with rehashing, the get_random_bytes() would directly move there. > atomic_set(&ht->nelems, 0); > atomic_set(&ht->shift, ilog2(tbl->size)); > RCU_INIT_POINTER(ht->tbl, tbl); > RCU_INIT_POINTER(ht->future_tbl, tbl); > > - if (!ht->p.hash_rnd) > - get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd)); > - > INIT_WORK(&ht->run_work, rht_deferred_worker); > > return 0; >