netdev - Re: dn_route.c momentarily exiting RCU read-side critical section

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Message-Id: <E1Ip0Vs-0002zP-00@gondolin.me.apana.org.au>
Date:	Mon, 05 Nov 2007 19:53:04 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	paulmck@...ux.vnet.ibm.com
Cc:	davem@...emloft.net, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, SteveW@....org, dipankar@...ibm.com
Subject: Re: dn_route.c momentarily exiting RCU read-side critical section

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
>> 
>> > net/decnet/dn_route.c in dn_rt_cache_get_next() is as follows:
>> > 
>> > static struct dn_route *dn_rt_cache_get_next(struct seq_file *seq, struct dn_route *rt)
>> > {
>> >     struct dn_rt_cache_iter_state *s = rcu_dereference(seq->private);
>> > 
>> >     rt = rt->u.dst.dn_next;
>> >     while(!rt) {
>> >             rcu_read_unlock_bh();
>> >             if (--s->bucket < 0)
>> >                     break;
>
> OK, for my next stupid question: why is the rcu_dereference(seq->private)
> required, as opposed to simply seq->private?

It was put there by someone who went through the code converting
all occurances of smp_read_barrier_depends to rcu_dereference.
In this instance the rcu_dereference conversion doesn't make much
sense so we should probably just revert it.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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