Re: [PATCH] ulog: add protection when remove ipt_ULOG

[Gao feng <gaofeng@cn.fujitsu.com>]

On 2013/02/19 00:52, Pablo Neira Ayuso wrote:
> On Mon, Feb 18, 2013 at 11:57:36AM +0800, Gao feng wrote:
> [...]
>>> I think this is very unlikely to happen. The removal of the module
>>> happens in user-context and the entire path to build and deliver the
>>> skb to user-space is protected is under spin_lock_bh, so scheduling
>>> is not possible.
>>
>> Doesn't spin_lock_bh only disable local cpu's bottom-half?
>> the task that remove the modules can run on other cpus at the same time.
>> I'm wrong?
> 
> That's right. But that will not happen since the removal of ipt_ULOG
> is protected by the module refcount, which is bumped for each iptables
> rule. So, you have to remove all rules using the ULOG target first to
> be able to rmmod that module, but then there is no chance to race with
> packets.

this calltrack doesn't add the refcount of moudule.
trace_packet->nf_log_packet->logger->logfn(ipt_logfn).
But when removing module,we call nf_log_unregister and
we can make sure only ulog_tg_exit uses ulog_buffer->skb,
So it's safe to don't add spin lock protect here.

I will send a v2 patchset to remove the spin lock protect
in ebt_ulog module.

Thanks!