netdev - Re: [PATCH net] neigh: Force garbage collection if an entry is deleted administratively

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Message-Id: <20131114.022356.1095983243221745109.davem@davemloft.net>
Date:	Thu, 14 Nov 2013 02:23:56 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	steffen.klassert@...unet.com
Cc:	yoshfuji@...ux-ipv6.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] neigh: Force garbage collection if an entry is
 deleted administratively

From: Steffen Klassert <steffen.klassert@...unet.com>
Date: Tue, 12 Nov 2013 09:57:14 +0100

> Since git commit 2724680 ("neigh: Keep neighbour cache entries if number
> of them is small enough."), we keep all neighbour cache entries if the
> number is below a threshold. But if we now delete an entry administratively
> and then try to replace this by a permanent one, we get -EEXIST because the
> old entry ist still in the table (in NUD_FAILED state).
> 
> So lets force a garbage collect if we delete an entry administratively.
> 
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>

I don't think this is a sufficient fix.

If some entity refers to this entry (refcnt != 1) then the forced
GC won't do anything, and this is very much possible.

It is the difficult situation mentioned in a comment in
neigh_flush_dev() below the "refcnt != 1" test there.
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