On Mon, Feb 15, 2016 at 4:50 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
> On Mon, Feb 15, 2016 at 04:11:22PM +0100, Dmitry Vyukov wrote:
>> Hello,
>>
>> While looking into some memory leaks of sctp ports I've noticed that
>> sctp_init initializes port hash table as follows:
>>
>> /* Allocate and initialize the SCTP port hash table. */
>> do {
>> sctp_port_hashsize = (1UL << order) * PAGE_SIZE /
>> sizeof(struct sctp_bind_hashbucket);
>> if ((sctp_port_hashsize > (64 * 1024)) && order > 0)
>> continue;
>> sctp_port_hashtable = (struct sctp_bind_hashbucket *)
>> __get_free_pages(GFP_KERNEL | __GFP_NOWARN, order);
>> } while (!sctp_port_hashtable && --order > 0);
>>
>> and then hash index is computed as follows:
>>
>> /* Warning: The following hash functions assume a power of two 'size'. */
>> /* This is the hash function for the SCTP port hash table. */
>> static inline int sctp_phashfn(struct net *net, __u16 lport)
>> {
>> return (net_hash_mix(net) + lport) & (sctp_port_hashsize - 1);
>> }
>>
>> I don't see what ensures that sctp_port_hashsize is in fact a power-of-2.
>>
>> spinlock_t in sctp_bind_hashbucket can be 2 words in some configs,
>> then sizeof(sctp_bind_hashbucket) == 24, which can render half of hash
>> table unused.
>>
>> struct sctp_bind_hashbucket {
>> spinlock_t lock;
>> struct hlist_head chain;
>> };
>>
>> Am I missing something?
>>
> You're right, its not. It seems to me that sctp_port_hashsize is meant to
> simply bound the upper index of the hashtable array, and as such the phashfn
> should not assume that its a power of 2 (i.e. it should simply mod the hash
> value by sctp_port_hashsize rather than and-ing it). Alternatively we could
> simply use alloc_large_system_hash to allocate this hash table here, the way tcp
> does. I'm traveling right now, but can take care of this as soon as i get home
> on wednesday
Hi Neil,
Thanks for confirming. It's yours, I don't pretend to fix it sooner.
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