Messages in this thread Patch in this message | | | Date | Tue, 21 May 2013 13:05:48 +0400 | From | Roman Gushchin <> | Subject | [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro |
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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))
#define hlist_nulls_next_rcu(node) \ (*((struct hlist_nulls_node __rcu __force **)&(node)->next)) -- 1.8.1.2
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