netdev - Re: Deadlock in IPv6 code while garbage collection on the rwlock protecting the routing tree.

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Message-Id: <20100123.022210.56302976.davem@davemloft.net>
Date:	Sat, 23 Jan 2010 02:22:10 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	djohnson@...rentnetworks.com, sakkiped@...rentnetworks.com,
	netdev@...r.kernel.org
Subject: Re: Deadlock in IPv6 code while garbage collection on the rwlock
 protecting the routing tree.

From: Stephen Hemminger <shemminger@...tta.com>
Date: Wed, 23 Dec 2009 10:13:09 -0800

> With RCU, you can safely acquire a spinlock inside rcu_read_lock
> section.  The only issue is that the entry being modified might already
> be in process of being deleted (ie. modifying a dead route).
> 
> Probably simpler to just get rid of rwlock entirely, go with a spinlock
> for now.  Reader/writer locks are slower than spin locks and even if
> lock is highly read contended, it is not held for long.
> 
> IPV6 routing table is using much simpler algorithms on the assumption
> that IPV6 was going to solve the CIDR address explosion problem. That
> assumption will probably not hold up, and having a trie (TRASH) version
> of IPV6 routing table with RCU would be a good research project for
> some graduate student.

This is all well and good, but meanwhile someone does need to
fix the deadlock originally reported here :-)
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