On 05/28/2015 06:13 PM, Eric Dumazet wrote:

This patch is not needed.

You really should read Documentation/RCU , because it looks like you are
quite confused.

When we remove an element from a RCU protected list, all the objects in
the chain are already ready to be caught by rcu readers.

Therefore, no additional memory barrier is needed before doing *np =
n->next;

Please do not add spurious memory barriers. Like atomic operations, we
want all of them being required and possibly documented.

Yes, you are right, thanks for your clear explanation :)
However, there are still three places where we use rcu_assign_pointer() to
remove a neigh entry from a RCU-protected list, and the three places are
neigh_forced_gc(), neigh_flush_dev(), and __neigh_for_each_release()
respectively. This means it's redundant for us to use rcu_assign_pointer() in
the three places, right?

Regards,
Ying