lkml.org 
[lkml]   [2008]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    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


    \
     
     \ /
      Last update: 2008-04-01 23:41    [W:2.513 / U:0.712 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site