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SubjectRe: [PATCH net-next 3/3] tap: XDP support
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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

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