linked lists, locking in softirq context -- no ideas ??

[Giacomo <delleceste@gmail.com>]

Hi to all...
do not know if the mailing list received this message - nobody can answer?

Thanks so much

giacomo


---------- Forwarded message ----------
From: Giacomo <delleceste@gmail.com>
Date: 2009/2/23
Subject: linked lists, locking in softirq context
To: netfilter-devel <netfilter-devel@vger.kernel.org>



Harald Welte's "The journey of a packet through the Linux 2.6.10
network stack" article says that packet travelling inside
linux kernel 2.6 (the receive / input part) runs in softirq context.

Hooking with netfilter's hooks in a kernel module, i need to read for
each packet received a list of rules.

Since in input and prerouting hooks the context is softirq (perhaps
also in forward?), I need some read lock
feature.

I currently use RCU lists and, while reading lists I use

READ

read_lock_bh()

together with list_for_each_rcu()

When changing, or flushing, rules, I use

WRITE

spin_lock() + list_add_tail_rcu() (adding)

or spin_lock() + list_for_each_entry() (for listing and then freeing
with list_del_rcu() and call_rcu() )

The question is:

- is the read part above correct? - do I really need _bh()? or should
I use simply read_lock() ?

Thanks in advance

Giacomo



--
Giacomo S.
http://www.giacomos.it

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-- 
Giacomo S.
http://www.giacomos.it

- - - - - - - - - - - - - - - - - - - - - -

* Aprile 2008: iqfire-wall, un progetto
  open source che implementa un
  filtro di pacchetti di rete per Linux,
  e` disponibile per il download qui:
  http://sourceforge.net/projects/ipfire-wall

* Informazioni e pagina web ufficiale:
  http://www.giacomos.it/iqfire/index.html

- - - - - - - - - - - - - - - - - - - - - -

 . ''  `.
:   :'    :
 `.  ` '
    `- Debian GNU/Linux -- The power of freedom
        http://www.debian.org
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