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SubjectRe: [patch 1/9] EMM Notifier: The notifier calls
On Tue, Apr 01, 2008 at 11:14:40PM +0200, Peter Zijlstra wrote:
> (Christoph, why are your CCs so often messed up?)
>
> On Tue, 2008-04-01 at 13:55 -0700, Christoph Lameter wrote:
> > plain text document attachment (emm_notifier)
>
> > +/* Register a notifier */
> > +void emm_notifier_register(struct emm_notifier *e, struct mm_struct *mm)
> > +{
> > + e->next = mm->emm_notifier;
> > + /*
> > + * The update to emm_notifier (e->next) must be visible
> > + * before the pointer becomes visible.
> > + * rcu_assign_pointer() does exactly what we need.
> > + */
> > + rcu_assign_pointer(mm->emm_notifier, e);
> > +}
> > +EXPORT_SYMBOL_GPL(emm_notifier_register);
> > +
> > +/* Perform a callback */
> > +int __emm_notify(struct mm_struct *mm, enum emm_operation op,
> > + unsigned long start, unsigned long end)
> > +{
> > + struct emm_notifier *e = rcu_dereference(mm)->emm_notifier;
> > + int x;
> > +
> > + while (e) {
> > +
> > + if (e->callback) {
> > + x = e->callback(e, mm, op, start, end);
> > + if (x)
> > + return x;
> > + }
> > + /*
> > + * emm_notifier contents (e) must be fetched after
> > + * the retrival of the pointer to the notifier.
> > + */
> > + e = rcu_dereference(e)->next;
> > + }
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(__emm_notify);
> > +#endif
>
> Those rcu_dereference()s are wrong. They should read:
>
> e = rcu_dereference(mm->emm_notifier);
>
> and
>
> e = rcu_dereference(e->next);

Peter has it right. You need to rcu_dereference() the same thing that
you rcu_assign_pointer() to.

Thanx, Paul


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