On Tue, Oct 30, 2007 at 01:10:36AM -0700, David Miller wrote:
> From: "Paul E. McKenney" <[email protected]>
> 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
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