locking while reading linked lists.

locking while reading linked lists.

[Giacomo]

Good morning.
In a packet filter which i wrote on my own, i have a linked list of structures
which i read periodically by means of list_for_each_safe macro.
These structures have a timer, when it expires, the entry is deleted.
The timer can on the other way be updated by mod_timer.

The context of execution is that of a software interrupt (i attach my code at
netfilter hooks), and some times (after tenths of millions of packets filtered)
the system goes into panic.

I think i should put some locks when reading in list_for_each or when
deleting an item, or when updating timers.

I thought it was not necessary because of the atomic context.

In fact, should i use read/write_lock? Or spinlocks?

Should i put the locks when reading in list_for_each, when adding an entry
with list_add, when deleting with list_del and also when mod_timer?

I verified that when i put those locks, things go better, but do i need them
so many in my code?

Thanks in advance

Giacomo.





--

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

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

Running `IPFIRE-wall` on debian GNU/Linux
http://www.giacomos.it/ipfire
http://www.debian.org

mailto:
delleceste@gmail.com
giacomo.strangolino@elettra.trieste.it
jacum@libero.it

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

Fwd: locking while reading linked lists.

[Giacomo]

---------- Forwarded message ----------
From: Giacomo <delleceste@gmail.com>
Date: 23-nov-2005 9.16
Subject: locking while reading linked lists.
To: netfilter devel <netfilter-devel@lists.netfilter.org>


Good morning.
In a packet filter which i wrote on my own, i have a linked list of structures
which i read periodically by means of list_for_each_safe macro.
These structures have a timer, when it expires, the entry is deleted.
The timer can on the other way be updated by mod_timer.

The context of execution is that of a software interrupt (i attach my code at
netfilter hooks), and some times (after tenths of millions of packets filtered)
the system goes into panic.

I think i should put some locks when reading in list_for_each or when
deleting an item, or when updating timers.

I thought it was not necessary because of the atomic context.

In fact, should i use read/write_lock? Or spinlocks?

Should i put the locks when reading in list_for_each, when adding an entry
with list_add, when deleting with list_del and also when mod_timer?

I verified that when i put those locks, things go better, but do i need them
so many in my code?

Thanks in advance

Giacomo.





--

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

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

Running `IPFIRE-wall` on debian GNU/Linux
http://www.giacomos.it/ipfire
http://www.debian.org

mailto:
delleceste@gmail.com
giacomo.strangolino@elettra.trieste.it
jacum@libero.it

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


--

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

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

Running `IPFIRE-wall` on debian GNU/Linux
http://www.giacomos.it/ipfire
http://www.debian.org

mailto:
delleceste@gmail.com
giacomo.strangolino@elettra.trieste.it
jacum@libero.it

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

Re: locking while reading linked lists.

[Stephen Hemminger]

On Wed, 23 Nov 2005 09:16:46 +0100
Giacomo <delleceste@gmail.com> wrote:

> Good morning.
> In a packet filter which i wrote on my own, i have a linked list of structures
> which i read periodically by means of list_for_each_safe macro.
> These structures have a timer, when it expires, the entry is deleted.
> The timer can on the other way be updated by mod_timer.
> 
> The context of execution is that of a software interrupt (i attach my code at
> netfilter hooks), and some times (after tenths of millions of packets filtered)
> the system goes into panic.
> 
> I think i should put some locks when reading in list_for_each or when
> deleting an item, or when updating timers.
> 
> I thought it was not necessary because of the atomic context.
> 
> In fact, should i use read/write_lock? Or spinlocks?

Learn how to use RCU. There is lots of info in Documentation/RCU/
and there are list macro's that make it painless.