netdev - Re: [RFC bpf-next 1/2] net: bridge: add unstable br_fdb_find_port_from

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Date:   Wed, 26 Jan 2022 13:03:56 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, dsahern@...nel.org,
        komachi.yoshiki@...il.com, brouer@...hat.com, memxor@...il.com,
        andrii.nakryiko@...il.com
Subject: Re: [RFC bpf-next 1/2] net: bridge: add unstable
 br_fdb_find_port_from_ifindex helper

Lorenzo Bianconi <lorenzo@...nel.org> writes:

>> > +	rcu_read_lock();
>> 
>> This is not needed when the function is only being called from XDP...
>
> don't we need it since we do not hold the rtnl here?

No. XDP programs always run under local_bh_disable() which "counts" as
an rcu_read_lock(); I did some cleanup around this a while ago, see this
commit for a longer explanation:

782347b6bcad ("xdp: Add proper __rcu annotations to redirect map entries")

-Toke