netdev - Re: [ROSE] [AX25] possible circular locking

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Message-ID: <20071218220410.GA15502@ami.dom.local>
Date:	Tue, 18 Dec 2007 23:04:10 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Pidoux <f6bvp@...e.fr>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Ralf Baechle DL5RB <ralf@...ux-mips.org>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [ROSE] [AX25] possible circular locking

On Tue, Dec 18, 2007 at 10:12:31PM +0100, Pidoux wrote:
> Hi,
>
> Thank you Jarek for the analysis of the circular locking dependency report.
> I applied the patch you proposed and it works well as soon as I am able to 
> reboot now without
> lock warning message and I can also killall kissattach.
>
> I tried also the patch without the loop, that is only spin_unlock_bh() 
> before calling
> ax25_disconnect() and spin_lock_bh() just after.
> It worked also well.
> However I must say that I only have one ax25 device running (ax0).
>
> Is the loop really necessary here ? in case there are more than one ax25 
> device ?
>
> Also, I will let my AX25 - ROSE application running in order to test the 
> system stability with the full patch.
> I will let you know the results in a while.

Thank you Bernard for the bravery!

The loop is only for debugging: I don't know exactly what is done
during this ax25_disconnect(), and how the list can change in the
meantime because of some other activities. So, it's e.g. against
possible list_del of this node - then some sockets would stay not
disconnected.

I think, it's up to Ralf or some other ax25 expert to judge if this
could be done like this. Since it's not used very often, I think
this should better stay during testing: if there are no warnings
- the loop isn't repeated; otherwise it could simply take a little
more time, but all sockets should be serviced, plus we know about
problems.

Thanks,
Jarek P.
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