netdev - Re: [PATCH bpf-next 1/8] xdp: simplify devmap cleanup

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Date:   Wed, 18 Dec 2019 12:14:59 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, davem@...emloft.net,
        jakub.kicinski@...ronome.com, hawk@...nel.org,
        john.fastabend@...il.com, magnus.karlsson@...el.com,
        jonathan.lemon@...il.com
Subject: Re: [PATCH bpf-next 1/8] xdp: simplify devmap cleanup

Björn Töpel <bjorn.topel@...il.com> writes:

> From: Björn Töpel <bjorn.topel@...el.com>
>
> After the RCU flavor consolidation [1], call_rcu() and
> synchronize_rcu() waits for preempt-disable regions (NAPI) in addition
> to the read-side critical sections. As a result of this, the cleanup
> code in devmap can be simplified
>
> * There is no longer a need to flush in __dev_map_entry_free, since we
>   know that this has been done when the call_rcu() callback is
>   triggered.
>
> * When freeing the map, there is no need to explicitly wait for a
>   flush. It's guaranteed to be done after the synchronize_rcu() call
>   in dev_map_free(). The rcu_barrier() is still needed, so that the
>   map is not freed prior the elements.
>
> [1] https://lwn.net/Articles/777036/
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>