Messages in this thread | | | Date | Tue, 21 May 2013 19:51:10 +0400 | From | Roman Gushchin <> | Subject | Re: [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro |
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On 21.05.2013 19:16, Eric Dumazet wrote: > 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 ?
If you think, that it will solve the problem, please, send a patch. I think, you are wrong here. If you think only that it will look better, I agree.
Regards, Roman
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