On Fri, Jul 28, 2017 at 11:50:45AM +0800, Jason Wang wrote: > > > On 2017年07月28日 11:46, Michael S. Tsirkin wrote: > > On Fri, Jul 28, 2017 at 11:28:54AM +0800, Jason Wang wrote: > > > > > + old_prog = rtnl_dereference(tun->xdp_prog); > > > > > + if (old_prog) > > > > > + bpf_prog_put(old_prog); > > > > > + rcu_assign_pointer(tun->xdp_prog, prog); > > > > Is this OK? Could this lead to the program getting freed and then > > > > datapath accessing a stale pointer? I mean in the scenario where the > > > > process gets pre-empted between the bpf_prog_put() and > > > > rcu_assign_pointer()? > > > Will call bpf_prog_put() after rcu_assign_pointer(). > > I suspect you need to sync RCU or something before that. > > __bpf_prog_put() will do call_rcu(), so looks like it was ok. > > Thanks
True - I missed that. -- MST
