netdev - Re: [PATCH 1/1][PKT_CLS] Avoid multiple tree locks

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Date:	Thu, 22 Mar 2007 12:36:17 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	hadi@...erus.ca
CC:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH 1/1][PKT_CLS] Avoid multiple tree locks

jamal wrote:
> On Wed, 2007-21-03 at 15:04 +0100, Patrick McHardy wrote:
> 
>>These (compile tested) patches demonstrate the idea. 
>>
>>The first one
>>lets netlink_kernel_create users specify a mutex that should be
>>held during dump callbacks, the second one uses this for rtnetlink
>>and changes inet_dump_ifaddr for demonstration.
>>
>>A complete patch would allow us to simplify locking in lots of
>>spots, all rtnetlink users currently need to implement extra
>>locking just for the dump functions, and a number of them
>>already get it wrong and seem to rely on the rtnl.
>>
> 
> 
> The mutex is certainly a cleaner approach;
> and a lot of the RCU protection would go away. I like it.

Not as much as I initially thought, but at least we would have
consistent locking for the dump callbacks.

> Knowing you i sense theres something clever in there that i am 
> missing. I dont see how you could get rid of the tree locking
> since we need to protect against the data path still, no?
> Or are you looking at that as a separate effort?

We can remove qdisc_tree_lock since with this patch all changes
and all tree walking happen under the RTNL. We still need to keep
dev->queue_lock for the data path.

I'll update the patches to include all rtnetlink users and repost
in a day or two.
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