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Date: Tue, 1 Dec 2020 16:17:20 -0800 From: Jakub Kicinski <kuba@...nel.org> To: Cong Wang <xiyou.wangcong@...il.com> Cc: netdev@...r.kernel.org, Dongdong Wang <wangdongdong@...edance.com>, Thomas Graf <tgraf@...g.ch>, bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com> Subject: Re: [Patch net] lwt: disable BH too in run_lwt_bpf() On Tue, 1 Dec 2020 16:16:33 -0800 Jakub Kicinski wrote: > On Tue, 1 Dec 2020 11:44:38 -0800 Cong Wang wrote: > > From: Dongdong Wang <wangdongdong@...edance.com> > > > > The per-cpu bpf_redirect_info is shared among all skb_do_redirect() > > and BPF redirect helpers. Callers on RX path are all in BH context, > > disabling preemption is not sufficient to prevent BH interruption. > > > > In production, we observed strange packet drops because of the race > > condition between LWT xmit and TC ingress, and we verified this issue > > is fixed after we disable BH. > > > > Although this bug was technically introduced from the beginning, that > > is commit 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure"), > > at that time call_rcu() had to be call_rcu_bh() to match the RCU context. > > So this patch may not work well before RCU flavor consolidation has been > > completed around v5.0. > > > > Update the comments above the code too, as call_rcu() is now BH friendly. > > > > Cc: Thomas Graf <tgraf@...g.ch> > > Cc: bpf@...r.kernel.org > > Reviewed-by: Cong Wang <cong.wang@...edance.com> > > Signed-off-by: Dongdong Wang <wangdongdong@...edance.com> > > Fixes? Ah, should have read the commit message first. Okay.
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