On Tue, 2013-05-21 at 18:47 +0400, Roman Gushchin wrote:
> On 21.05.2013 17:44, Eric Dumazet wrote:
> > On Tue, 2013-05-21 at 05:09 -0700, Paul E. McKenney wrote:
> >
> >>>
> >>> -#define hlist_nulls_first_rcu(head) \
> >>> - (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
> >>> +#define hlist_nulls_first_rcu(head) \
> >>> + (*((struct hlist_nulls_node __rcu __force **) \
> >>> + &((volatile typeof(*head) *)head)->first))
> >>
> >> Why not use ACCESS_ONCE() or (better) rcu_dereference_raw() here?
> >
> > More exactly we have :
> >
> > #define list_entry_rcu(ptr, type, member) \
> > ({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr;
> > \
> > container_of((typeof(ptr))rcu_dereference_raw(__ptr), type,
> > member); \
> > })
> >
> > #define list_for_each_entry_rcu(pos, head, member) \
> > for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
> > &pos->member != (head); \
> > pos = list_entry_rcu(pos->member.next, typeof(*pos),
> > member))
> > << and >>
> >
> > #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)
> > \
> > for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));
> > \
> > (!is_a_nulls(pos)) &&
> > \
> > ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member);
> > 1; }); \
> > pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
> >
> > We need to change hlist_nulls_for_each_entry_rcu() to use same construct,
> > so that the rcu_dereference_raw() is performed at the right place.
>
> No.
>
> This code has the same mistake: it is rcu_dereference_raw(head->first),
> so there is nothing that prevents gcc to store the (head->first) value
> in a register.
Please read again what I wrote, you misundertood.
hlist_nulls_for_each_entry_rcu() should use same construct than
list_for_each_entry_rcu(), and not use rcu_dereference_raw()
Is that clear, or do you want me to send the patch ?
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