Re: [Xenomai] rtnet locking/socket SKBs

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Thu, Jun 04, 2015 at 01:09:08PM +0200, Marc Strämke wrote:
> Gilles,
> 
> Am Donnerstag, 4. Juni 2015, 12:56:16 schrieb Gilles Chanteperdrix:
> > The previous rtnet design was converted to reference counts globally
> > when integrating into xenomai 3, some details may still need fixing.
> > The old design was different but lead to the close syscall looping
> > for ever and blocking your application if anything went wrong, so,
> > this is an attempt to avoid this issue.
> Yes I do understand this. I am just trying to figure out what the right fix is. 
> If I just disable incrementing the fd reference count (see attached patch) 
> AF_PACKET works as it should.  From my current understanding of the code the 
> reference counting for the SKB Pools attached to a socket is redundant, but 
> I've only closely inspected AF_PACKET not the other sockets in the IP stack.

The locking of the pools is not redundant. The reason for this lock
is that when an skb is in between two pools, we do not want the pool
it comes from to be destroyed, as the skb would end-up leaking. So,
since skbs move from pool to pool, when the skb comes to a new pool,
the old pool should be unlocked. This should work as rtnet spends
its time exchanging skbs from pool to pool and does not allocate or
free them. I tried and implement something along these lines.
Apparently, I messed up, but the fix is not to disable the locking.
Disabling locking will lead to leaking skbs.

-- 
					    Gilles.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 811 bytes
Desc: not available
URL: <http://xenomai.org/pipermail/xenomai/attachments/20150604/2c14ad2d/attachment.sig>