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

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Message-Id: <20130611.142229.497972115797274443.davem@davemloft.net>
Date:	Tue, 11 Jun 2013 14:22:29 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mkubecek@...e.cz
Cc:	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

From: Michal Kubecek <mkubecek@...e.cz>
Date: Tue, 11 Jun 2013 22:49:12 +0200

> On Tue, Jun 11, 2013 at 01:01:14PM -0700, David Miller wrote:
>> From: Michal Kubecek <mkubecek@...e.cz>
>> Date: Tue, 11 Jun 2013 12:07:18 +0200
>> 
>> > On Mon, Jun 10, 2013 at 02:26:42PM -0700, David Miller wrote:
>> >> 
>> >> It seems to me that it would be much simpler to simply update
>> >> ip6_rt_last_gc first, that way the other threads would elide the GC
>> >> call.
>> > 
>> > 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.
>> 
>> Why don't you simply try it and find out?
> 
> I don't have the system where the issue was observed at hand. I'll have
> to ask the customer who reported it to run the test so that it may take
> some time.

Please also take care of the issue Eric mentioned, in that some GC
calls erroneously do not update the last GC timestamp.
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