On Wed, Jul 24, 2024 at 07:57:42AM -0700, Jakub Kicinski wrote: > On Wed, 24 Jul 2024 01:46:11 +0200 Maciej Fijalkowski wrote: > > Goal of this commit was to prevent compiler from code reoder such as NAPI > > is launched before update of xsk_buff_pool pointer which is achieved with > > WRITE_ONCE()/synchronize_net() pair. Then per my understanding single > > READ_ONCE() within NAPI was sufficient, the one that makes the decision > > which Rx routine should be called (zc or standard one). Given that bh are > > disabled and updater respects RCU grace period IMHO pointer is valid for > > current NAPI cycle. > > So if we are already in the af_xdp handler, and update patch sets pool > to NULL - the af_xdp handler will be fine with the pool becoming NULL? > I guess it may be fine, it's just quite odd to call the function called > _ONCE() multiple times.. Update path before NULLing pool will go through rcu grace period, stop napis, disable irqs, etc. Running napi won't be exposed to nulled pool in such case. >
