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Date: Tue, 30 Oct 2007 08:12:54 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: David Miller <davem@...emloft.net> Cc: 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 On Tue, Oct 30, 2007 at 01:10:36AM -0700, David Miller wrote: > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> > Date: Mon, 29 Oct 2007 14:15:40 -0700 > > > 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; > > > > ... But what happens if seq->private is freed up right here? > > ... Or what prevents this from happening? > ... > > Similar code is in rt_cache_get_next(). > > > > So, what am I missing here? > > seq->private is allocated on file open (here via seq_open_private()), > and freed up on file close (via seq_release_private). > > So it cannot be freed up in the middle of an iteration. Thank you for the info!!! OK, for my next stupid question: why is the rcu_dereference(seq->private) required, as opposed to simply seq->private? Thanx, Paul - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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