netdev - Re: [PATCH 1/1] bonding: eliminate RTNL assertion spew

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Date:	Tue, 9 Jan 2007 18:34:58 -0500
From:	Andy Gospodarek <andy@...yhouse.net>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Andy Gospodarek <andy@...yhouse.net>, fubar@...ibm.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] bonding: eliminate RTNL assertion spew

On Tue, Jan 09, 2007 at 06:13:55PM -0500, Jeff Garzik wrote:
> Andy Gospodarek wrote:
> >-void bond_alb_handle_active_change(struct bonding *bond, struct slave 
> >*new_slave)
> >+void bond_alb_handle_active_change(struct bonding *bond, struct slave 
> >*new_slave, int rtnl_locked)
> > {
> > 	struct slave *swap_slave;
> > 	int i;
> 
> Although this is not a direct NAK (haven't read the full patch yet), 
> conditional locking behavior like this is /very/ fragile, and in Linux 
> is generally discouraged.  Vendor drivers in particular have a history 
> of constantly getting this wrong, and it makes locking more difficult to 
> review.
> 
> 	Jeff
> 

I'd be happy to propose something that doesn't do conditional locking
like this.  I saw this route as a way to take the rtnl lock only when it
was absolutely necessary.  After spending some time trying to get it
right I can understand why it is so discouraged.  I'd also rather not
provide a 'bad example' for how to do things. :-)

If others are OK with it, I'd be happy to propose a patch like Stephen
suggested where the lock is taken in the mii/arp monitor routines.
Though the locking would be unnecessary in some cases it would be much
cleaner and easier to maintain.

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