netdev - Re: [PATCH] virtio_net: add local_bh_disable() around u64_stats_update

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Message-ID: <0dce3017-9973-af2d-f324-6fe8b5eb5469@lab.ntt.co.jp>
Date:   Thu, 18 Oct 2018 18:06:57 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        tglx@...utronix.de, "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] virtio_net: add local_bh_disable() around
 u64_stats_update_begin

On 2018/10/18 17:43, Sebastian Andrzej Siewior wrote:
> on 32bit, lockdep notices that virtnet_open() and refill_work() invoke
> try_fill_recv() from process context while virtnet_receive() invokes the
> same function from BH context. The problem that the seqcounter within
> u64_stats_update_begin() may deadlock if it is interrupted by BH and
> then acquired again.
> 
> Introduce u64_stats_update_begin_bh() which disables BH on 32bit
> architectures. Since the BH might interrupt the worker, this new
> function should not limited to SMP like the others which are expected
> to be used in softirq.
> 
> With this change we might lose increments but this is okay. The
> important part that the two 32bit parts of the 64bit counter are not
> corrupted.
> 
> Fixes: 461f03dc99cf6 ("virtio_net: Add kick stats").
> Suggested-by: Stephen Hemminger <stephen@...workplumber.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

NACK. Again, this race should not happen because of NAPI guard.
We need to investigate why this warning happened.

-- 
Toshiaki Makita