From: Jarek Poplawski <jarkao2@gmail.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Eric Dumazet <dada1@cosmosbay.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
davem@davemloft.net, dipankar@in.ibm.com, netdev@vger.kernel.org
Subject: Re: [NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt_cache
Date: Fri, 11 Jan 2008 09:30:10 +0100 [thread overview]
Message-ID: <20080111083010.GA2183@ff.dom.local> (raw)
In-Reply-To: <20080111000020.GB22040@gondor.apana.org.au>
On Fri, Jan 11, 2008 at 11:00:20AM +1100, Herbert Xu wrote:
> On Fri, Jan 11, 2008 at 12:10:42AM +0100, Jarek Poplawski wrote:
> >
> > It seems this optimization could've a side effect: if during such a
> > loop updates are done, and r is seen !NULL during while() check, but
> > NULL after rcu_dereference(), the listing/counting could stop too
> > soon. So, IMHO, probably the first version of this patch is more
> > reliable. (Or alternatively additional check is needed before return.)
>
> No, while the value of r->u.dst.rt_next can change between two readings,
> the value of r cannot.
...Then, of course, it's O.K.!
It looks like I'm really too lazy and/or these selfdocumenting features
of RCU are a bit overrated: one can never be sure which pointer is
really RCU protected without checking a few places?! So, after looking
at this rt_cache_get_next() and this patch only, it's looks like the
third candidate after seq->private and rtable...
Thanks for explanation and sorry for disturbing!
Jarek P.
next prev parent reply other threads:[~2008-01-11 8:23 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-07 18:30 [IPV4] ROUTE: ip_rt_dump() is unecessary slow Eric Dumazet
2008-01-08 5:52 ` David Miller
2008-01-08 6:11 ` Eric Dumazet
2008-01-08 6:15 ` David Miller
2008-01-08 6:37 ` Eric Dumazet
2008-01-09 6:02 ` Herbert Xu
2008-01-09 7:38 ` [NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt_cache Eric Dumazet
2008-01-09 9:46 ` Herbert Xu
2008-01-09 10:37 ` Eric Dumazet
2008-01-09 14:22 ` Paul E. McKenney
2008-01-09 14:31 ` David Miller
2008-01-09 14:43 ` Paul E. McKenney
2008-01-09 17:36 ` Eric Dumazet
2008-01-10 11:56 ` David Miller
2008-01-10 14:06 ` [DECNET] ROUTE: fix rcu_dereference() uses in /proc/net/decnet_cache Eric Dumazet
2008-01-11 6:35 ` David Miller
2008-01-10 23:10 ` [NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt_cache Jarek Poplawski
2008-01-10 23:51 ` Paul E. McKenney
2008-01-11 14:13 ` Jarek Poplawski
2008-01-11 0:00 ` Herbert Xu
2008-01-11 8:30 ` Jarek Poplawski [this message]
2008-01-11 9:11 ` Jarek Poplawski
2008-01-11 9:23 ` Jarek Poplawski
2008-01-11 10:38 ` Herbert Xu
2008-01-11 11:30 ` Jarek Poplawski
2008-01-11 10:37 ` Herbert Xu
2008-01-11 12:31 ` Jarek Poplawski
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