netdev - Re: [PATCH stable 3.4 1/2] ipv4: move route garbage collector to work queue

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Message-Id: <1407885074.3535486.152056309.7BDE2766@webmail.messagingengine.com>
Date:	Wed, 13 Aug 2014 01:11:14 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>, hannes@...hat.com
Cc:	eric.dumazet@...il.com, mleitner@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH stable 3.4 1/2] ipv4: move route garbage collector to work
 queue

On Wed, Aug 13, 2014, at 00:42, David Miller wrote:
> The second patch, on the other hand, needs some more thought.  It is
> changing behavior, in that cases that would have succeeded in the past
> will now potentially fail only because the neighbour cache limits were
> hit at an unlucky moment (when an async GC was going already).
> 
> If this happens from a software interrupt, we'll fail instantly
> because attempts starts at 0.

Hmhmhm, a truly valid concern.

> Just bite the bullet and put a spinlock around the GC operation.

We had a spinlock around the GC operation at first but still were
capable to cause softlockups, I don't remember if a complete lockup
happend.

> The async GCs are normal on a loaded machine, whereas the neighbour
> tables filling up is much less so.  I think having the neighbout
> overflow path synchronize with async GCs is therefore not going to be
> a real problem in practice.

Thanks for your comments, we look into it. Should be no problem to
conditional synchronize with the neighbour overflow path.

Thanks,
Hannes
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