On Tue, Oct 10, 2017 at 5:32 AM, Alexander Aring <ar...@mojatatu.com> wrote: > This patch fixes an issue with kfree_rcu which is not protected by RTNL > lock. It could be that the current assigned rcu pointer will be freed by > kfree_rcu while dump callback is running.
Why? kfree_rcu() respects existing readers, so why this could happen? > > To prevent this, we call rcu_synchronize at first. Then we are sure all > latest rcu functions e.g. rcu_assign_pointer and kfree_rcu in init are > done. After rcu_synchronize we dereference under RTNL lock which is also > held in init function, which means no other rcu_assign_pointer or > kfree_rcu will occur. If you really want to wait for kfree_rcu(), rcu_barrier() is the one instead of rcu_synchronize(). Just FYI. > > To call rcu_synchronize will also prevent weird behaviours by doing over > netlink: > > - set params A > - set params B > - dump params > \--> will dump params A What's wrong with this? Existing readers could still read old data, which is _perfectly_ fine as long as we don't free the old data before they are gone.
