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
