Newbie Question: Locking in Netfilter hook module?

Newbie Question: Locking in Netfilter hook module?

[Ned Ren]

Hi, 

This maybe a silly question. I'm wondering for hook modules that I write for netfilter, is it
necessary to do locking (critical section) when accessing my own global structures? This is
regarding SINGLE CPU systems, is there anything that would preempt my module while it's at it such
as interrupt etc?

Thank you!

please reply to my email addr as well: nedren@yahoo.com


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Re: Newbie Question: Locking in Netfilter hook module?

[Harald Welte]

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On Fri, Jul 11, 2003 at 01:58:49AM -0700, Ned Ren wrote:
> Hi, 
> 
> This maybe a silly question. I'm wondering for hook modules that I
> write for netfilter, is it necessary to do locking (critical section)
> when accessing my own global structures? 

Yes, it is always necessarry to lock your global structures.  All of
netfilter is running in softirq context.

> This is regarding SINGLE CPU systems, is there anything that would
> preempt my module while it's at it such as interrupt etc?

hard interrupts can always interrupt a softirq - but a softirq doesn't
interrupt another softirq (on single cpu).

However, all kernel code _has_ to be SMP safe.

> Thank you!

-- 
- Harald Welte <laforge@netfilter.org>             http://www.netfilter.org/
============================================================================
  "Fragmentation is like classful addressing -- an interesting early
   architectural error that shows how much experimentation was going
   on while IP was being designed."                    -- Paul Vixie

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