netdev - Re: IPv4/IPv6 sysctl unregistration deadlock

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Date:	Tue, 03 Mar 2009 00:48:29 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	kaber@...sh.net
Cc:	greearb@...delatech.com, shemminger@...tta.com,
	ebiederm@...ssion.com, herbert@...dor.apana.org.au,
	netdev@...r.kernel.org
Subject: Re: IPv4/IPv6 sysctl unregistration deadlock

From: Patrick McHardy <kaber@...sh.net>
Date: Tue, 03 Mar 2009 00:03:00 +0100

> David Miller wrote:
> > From: Patrick McHardy <kaber@...sh.net>
> > Date: Mon, 02 Mar 2009 23:20:49 +0100
> > 
> >> This looks like its working fine. Despite the non-desirable active
> >> spinning, this seems like the best fix (actually much simpler than
> >> I expected to be possible) at this time. If we just could avoid
> >> the spinning when unnecessary, it would be perfect :)
> > Could you give that "not actually in-progress" detection a shot?
> > I don't like the spinning either.
> 
> I tried this morning, the problem is that its always the sysctl
> handler which will run into the deadlock first, but there is no
> reliable indication to avoid it other than that the RTNL is
> already held. The problem is that the sysctl interface puts the
> process holding the RTNL to sleep and allows a process requiring
> it to run. Any different synchronization attempt will have the
> same problem, it seems you simply can't hold any locks while
> unregistering sysctls.

Ok, I applied Stephen's patches then...
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