netdev - Re: [PATCH v4 bpf-next 6/9] bpf: cpumap: implement XDP_REDIRECT for eBPF programs attached to map entries

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Message-ID: <20200626094934.49f9a94e@carbon>
Date:   Fri, 26 Jun 2020 09:49:34 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, davem@...emloft.net, ast@...nel.org,
        toke@...hat.com, lorenzo.bianconi@...hat.com, dsahern@...nel.org,
        andrii.nakryiko@...il.com, brouer@...hat.com
Subject: Re: [PATCH v4 bpf-next 6/9] bpf: cpumap: implement XDP_REDIRECT for
 eBPF programs attached to map entries

On Thu, 25 Jun 2020 23:28:59 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:

> > @@ -276,7 +286,10 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >   		}
> >   	}
> >   
> > -	rcu_read_unlock();
> > +	if (stats->redirect)
> > +		xdp_do_flush_map();
> > +
> > +	rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
> >   	xdp_clear_return_frame_no_direct();  
> 
> Hm, this looks incorrect. Why do you call the xdp_clear_return_frame_no_direct() /after/
> the possibility where there is a rescheduling point for softirq?

Good you caught this! - This needs to be fixed.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer