list_first_or_null() should test whether the list is empty and return pointer to the first entry if not in a RCU safe manner. It's broken in two ways.
* It compares __kernel @__ptr with __rcu @__next triggering the following sparse warning. net/core/dev.c:4331:17: error: incompatible types in comparison expression (different address spaces) * It doesn't perform rcu_dereference*() and computes the entry address using container_of() directly from the __rcu pointer which is inconsitent with other rculist interface. As a result, all three in-kernel users - net/core/dev.c, macvlan, cgroup - are buggy. They dereference the pointer w/o going through read barrier. Fix it by making list_first_or_null_rcu() dereference ->next directly and then use list_entry_rcu() on it like other rculist accessors. Signed-off-by: Tejun Heo <[email protected]> Reported-by: Fengguang Wu <[email protected]> Cc: Dipankar Sarma <[email protected]> Cc: "Paul E. McKenney" <[email protected]> Cc: "David S. Miller" <[email protected]> Cc: Li Zefan <[email protected]> Cc: Patrick McHardy <[email protected]> Cc: [email protected] --- include/linux/rculist.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -267,8 +267,9 @@ static inline void list_splice_init_rcu( */ #define list_first_or_null_rcu(ptr, type, member) \ ({struct list_head *__ptr = (ptr); \ - struct list_head __rcu *__next = list_next_rcu(__ptr); \ - likely(__ptr != __next) ? container_of(__next, type, member) : NULL; \ + struct list_head *__next = __ptr->next; \ + likely(__ptr != __next) ? \ + list_entry_rcu(__next, type, member) : NULL; \ }) /** -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
