Messages in this thread | | | Date | Tue, 21 May 2013 05:09:07 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro |
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On Tue, May 21, 2013 at 01:05:48PM +0400, Roman Gushchin wrote: > Hi, all! > > This is a fix for a problem described here: > https://lkml.org/lkml/2013/4/16/371 . > --- > > Some network functions (udp4_lib_lookup2(), for instance) use the > hlist_nulls_for_each_entry_rcu macro in a way that assumes restarting > of a loop. In this case, it is strictly necessary to reread the head->first > value from the memory before each scan. > Without additional hints, gcc caches this value in a register. In this case, > if a cached node is moved to another chain during the scan, we can loop > forever getting wrong nulls values and restarting the loop uninterruptedly. > > Signed-off-by: Roman Gushchin <klamm@yandex-team.ru> > Reported-by: Boris Zhmurov <zhmurov@yandex-team.ru> > --- > include/linux/rculist_nulls.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h > index 2ae1371..efd51bf 100644 > --- a/include/linux/rculist_nulls.h > +++ b/include/linux/rculist_nulls.h > @@ -37,8 +37,9 @@ static inline void hlist_nulls_del_init_rcu(struct > hlist_nulls_node *n) > } > } > > -#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?
Thanx, Paul
> #define hlist_nulls_next_rcu(node) \ > (*((struct hlist_nulls_node __rcu __force **)&(node)->next)) > -- > 1.8.1.2 >
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