Messages in this thread | | | Date | Tue, 1 Apr 2008 14:38:11 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [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
| |