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

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Date:	Wed, 21 Mar 2007 15:06:02 +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

Patrick McHardy wrote:
> Patrick McHardy wrote:
> 
>>>Alexey just explained to me why we do need qdisc_tree_lock in private
>>>mail. While dumping only the first skb is filled under the RTNL,
>>>while filling further skbs we don't hold the RTNL anymore. So I will
>>>probably have to drop that patch.
>>
>>
>>
>>What we could do is replace the netlink cb_lock spinlock by a
>>user-supplied mutex (supplied to netlink_kernel_create, rtnl_mutex
>>in this case). That would put the entire dump under the rtnl and
>>allow us to get rid of qdisc_tree_lock and avoid the need to take
>>dev_base_lock during qdisc dumping. Same in other spots like
>>rtnl_dump_ifinfo, inet_dump_ifaddr, ...
> 
> 
> 
> 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.
> 
> If there are no objections to this change I'm going to update
> the second patch to include all rtnetlink users


D'oh .. wrong patches.




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