Re: BUG: unable to handle kernel paging request in bpf_dispatcher_xdp

Jakub Kicinski
2022-12-09T23:34:53Z

On Sat, 10 Dec 2022 00:32:07 +0100 Daniel Borkmann wrote:
> fwiw, these should not be necessary, Documentation/RCU/checklist.rst :
>
> [...] One example of non-obvious pairing is the XDP feature in networking,
> which calls BPF programs from network-driver NAPI (softirq) context. BPF
> relies heavily on RCU protection for its data structures, but because the
> BPF program invocation happens entirely within a single local_bh_disable()
> section in a NAPI poll cycle, this usage is safe. The reason that this usage
> is safe is that readers can use anything that disables BH when updaters use
> call_rcu() or synchronize_rcu(). [...]

FWIW I sent a link to the thread to Paul and he confirmed
the RCU will wait for just the BH.