concurrency problems in a netfilter target extension?

concurrency problems in a netfilter target extension?

[Tobias Koeck]

I´m writing on a netfilter target extension.

Are there some possible concurrency problems (means is it possible that 
my target extension modules is loaded several times or could it be used 
with several cpu cores simultaniously)?

If yes what is the best solution for that (which locking functions)?

Greetings and thanks
Tobias

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Re: concurrency problems in a netfilter target extension?

[Jan Engelhardt]

On Thursday 2008-07-31 10:17, Tobias Koeck wrote:

> I´m writing on a netfilter target extension.
>
> Are there some possible concurrency problems (means is it possible that my
> target extension modules is loaded several times or could it be used with
> several cpu cores simultaniously)?

Yes, see "Writing your own Netfilter modules" at 
http://jengelh.medozas.de/ , chapter "tricks and traps"
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Re: concurrency problems in a netfilter target extension?

[Tobias Koeck]

I've read that. But does it solve the problem in a target extension
module? Will the modules only be cloned so that you have different
data structures? Or is only one instance in the memory and if one
processor changes something every other threads will use the changed
values?

On Thu, Jul 31, 2008 at 2:39 PM, Jan Engelhardt <jengelh@medozas.de> wrote:
>
> On Thursday 2008-07-31 10:17, Tobias Koeck wrote:
>
>> I´m writing on a netfilter target extension.
>>
>> Are there some possible concurrency problems (means is it possible that my
>> target extension modules is loaded several times or could it be used with
>> several cpu cores simultaniously)?
>
> Yes, see "Writing your own Netfilter modules" at
> http://jengelh.medozas.de/ , chapter "tricks and traps"
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Re: concurrency problems in a netfilter target extension?

[Jan Engelhardt]

On Thursday 2008-07-31 13:21, Tobias Koeck wrote:

>I've read that. But does it solve the problem in a target extension
>module? Will the modules only be cloned so that you have different
>data structures?

Which is why you allocate a separate structure, then let Netfilter clone 
it (shallow only) for percpu, so that in the end, you have one shared
structure regardless of the cloning operation.

>Or is only one instance in the memory and if one
>processor changes something every other threads will use the changed
>values?

Using this shared structure is then easy.