netdev - Re: [PATCH net] ipv6: prevent fib6_run

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Message-ID: <1370947206.3252.27.camel@edumazet-glaptop>
Date:	Tue, 11 Jun 2013 03:40:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michal Kubecek <mkubecek@...e.cz>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net
Subject: Re: [PATCH net] ipv6: prevent fib6_run_gc() contention

On Tue, 2013-06-11 at 12:07 +0200, Michal Kubecek wrote:

> That was my original idea but I was afraid that while the remaining
> window in ip6_dst_gc() would be very short and probably safe, we could
> still run into problem if fib6_gc_lock was locked by some other caller
> of fib6_run_gc() which doesn't update net->ipv6.ip6_rt_last_gc,
> especially via a timer.

This looks a bug (but not a big one) to me : 

We should update ip6_rt_last_gc if we did a gc,
not only from ip6_dst_gc()

So, I would move the "net->ipv6.ip6_rt_last_gc = now;" from ip6_dst_gc()
to fib6_run_gc(), right after the spin_lock_bh() ?




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