From: Gao feng <gaofeng@cn.fujitsu.com>
To: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
Josh Hunt <johunt@akamai.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"kaber@trash.net" <kaber@trash.net>,
Debabrata Banerjee <dbavatar@gmail.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"yoshfuji@linux-ipv6.org" <yoshfuji@linux-ipv6.org>,
"jmorris@namei.org" <jmorris@namei.org>,
"pekkas@netcore.fi" <pekkas@netcore.fi>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Bug in net/ipv6/ip6_fib.c:fib6_dump_table()
Date: Fri, 22 Jun 2012 11:34:08 +0800 [thread overview]
Message-ID: <4FE3E7B0.3020802@cn.fujitsu.com> (raw)
In-Reply-To: <20120621215056.GA24908@ms2.inr.ac.ru>
于 2012年06月22日 05:50, Alexey Kuznetsov 写道:
> On Thu, Jun 21, 2012 at 10:27:49PM +0200, Eric Dumazet wrote:
>> Looking at this code, it lacks proper synchronization
>> between tree updaters and tree walkers.
>>
>> fib6_walker_lock rwlock is not enough to prevent races.
>
> Hmm. As author of this weird code, I must say I honestly believed it was correct.
> At least I tried. :-)
>
>
> What's about 2bec5a336.., it does not look reasonable.
> The idea was that when you change tree, you fixup sleeping walkers, moving
> their location in tree to correct point. So, walkers must not have any stale pointers
> at any times (except when you under table write lock) and no skips/counts are required.
> I remember how damn difficult was it to make this right (well, sorry, if it is not yet :-)),
> so that understand that if some update is forgotten or done incorrectly, it is not so easy to find,
> but it is definitely worth of efforts.
Actually, I spent two months to try to reproduce this crash four months ago,
But finally I give up, I don't think there was any stale pointers,
we already correct it when we change the tree.
next prev parent reply other threads:[~2012-06-22 3:34 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-12 17:22 Bug in net/ipv6/ip6_fib.c:fib6_dump_table() Debabrata Banerjee
2012-06-21 19:35 ` Josh Hunt
2012-06-21 20:27 ` Eric Dumazet
2012-06-21 21:50 ` Alexey Kuznetsov
2012-06-22 3:34 ` Gao feng [this message]
2012-06-22 6:49 ` Josh Hunt
2012-06-22 8:29 ` Eric Dumazet
2012-06-22 13:44 ` Josh Hunt
2012-06-22 18:13 ` Eric Dumazet
2012-06-22 21:12 ` Debabrata Banerjee
2012-06-23 0:02 ` David Miller
2012-06-23 5:37 ` Eric Dumazet
2012-06-23 20:55 ` Alexey Kuznetsov
2012-06-23 23:02 ` David Miller
2012-06-25 22:40 ` David Miller
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