netdev - Re: [Devel] Re: [PATCH 2/5] net: Make rtnetlink infrastructure network namespace aware

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Date:	Sun, 30 Sep 2007 17:13:15 +0400
From:	"Denis V. Lunev" <dlunev@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Patrick McHardy <kaber@...sh.net>,
	Linux Containers <containers@...ts.osdl.org>,
	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [Devel] Re: [PATCH 2/5] net: Make rtnetlink infrastructure network
 namespace aware

Hmm, so it looks like we do not need this queue processing at all...

Regards,
	Den

Eric W. Biederman wrote:
> Patrick McHardy <kaber@...sh.net> writes:
> 
>> Maybe I can save you some time: we used to do down_trylock()
>> for the rtnl mutex, so senders would simply return if someone
>> else was already processing the queue *or* the rtnl was locked
>> for some other reason. In the first case the process already
>> processing the queue would also process the new messages, but
>> if it the rtnl was locked for some other reason (for example
>> during module registration) the message would sit in the
>> queue until the next rtnetlink sendmsg call, which is why
>> rtnl_unlock does queue processing. Commit 6756ae4b changed
>> the down_trylock to mutex_lock, so senders will now simply wait
>> until the mutex is released and then call netlink_run_queue
>> themselves. This means its not needed anymore.
> 
> Sounds reasonable.
> 
> I started looking through the code paths and I currently cannot
> see anything that would leave a message on a kernel rtnl socket.
> 
> However I did a quick test adding a WARN_ON if there were any messages
> found in the queue during rtnl_unlock and I found this code path
> getting invoked from linkwatch_event.  So there is clearly something I
> don't understand, and it sounds at odds just a bit from your
> description.
> 
> If we can remove the extra queue processing that would be great,
> as it looks like a nice way to simplify the locking and the special
> cases in the code.
> 
> Eric

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