netdev - Re: [PATCH] reduce the spinlock conflict during massive connect

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 6 Nov 2017 14:48:01 +0800
From:   Liu Yu <liuyu924@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller <davem@...emloft.net>,Alexey Kuznetsov
        <kuznet@....inr.ac.ru>,Hideaki YOSHIFUJI" <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH] reduce the spinlock conflict during massive connect

On Mon, Nov 6, 2017 at 1:27 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2017-11-06 at 10:28 +0800, Liu Yu wrote:
>> From: Liu Yu <allanyuliu@...cent.com>
>>
>> When a mount of processes connect to the same port at the same address
>> simultaneously, they are likely getting the same bhash and therefore
>> conflict with each other.
>>
>> The more the cpu number, the worse in this case.
>>
>> Use spin_trylock instead for this scene, which seems doesn't matter
>> for common case.
>>
>> Signed-off-by: Liu Yu <allanyuliu@...cent.com>
>> ---
>>  net/ipv4/inet_hashtables.c |    6 +++++-
>>  1 files changed, 5 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
>> index e7d15fb..cc11ec7 100644
>> --- a/net/ipv4/inet_hashtables.c
>> +++ b/net/ipv4/inet_hashtables.c
>> @@ -581,13 +581,17 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
>>  other_parity_scan:
>>       port = low + offset;
>>       for (i = 0; i < remaining; i += 2, port += 2) {
>> +             int ret;
>> +
>>               if (unlikely(port >= high))
>>                       port -= remaining;
>>               if (inet_is_local_reserved_port(net, port))
>>                       continue;
>>               head = &hinfo->bhash[inet_bhashfn(net, port,
>>                                                 hinfo->bhash_size)];
>> -             spin_lock_bh(&head->lock);
>> +             ret = spin_trylock(&head->lock);
>> +             if (unlikely(!ret))
>> +                     continue;
>>
>>               /* Does not bother with rcv_saddr checks, because
>>                * the established check is already unique enough.
>
> This is broken.
>
> I am pretty sure you have not really tested this patch properly.
>
> Chances are very high that a connect() will miss slots and wont succeed,
> when table is almost full.

Thanks for your comments!

Can you explain how connect() miss slots when table is almost full?

>
> Performance is nice, but we actually need to allocate a 4-tuple in a
> more deterministic fashion.
>

So, what's the 4th element would you suggest?