netdev - Re: [RFC PATCH 04/11] hv_netvsc: Disable NAPI before closing the VMBus channel

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Message-ID: <20200326082636.1d777921@hermes.lan>
Date:   Thu, 26 Mar 2020 08:26:36 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, linux-hyperv@...r.kernel.org,
        Michael Kelley <mikelley@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 04/11] hv_netvsc: Disable NAPI before closing the
 VMBus channel

On Wed, 25 Mar 2020 23:54:58 +0100
"Andrea Parri (Microsoft)" <parri.andrea@...il.com> wrote:

> vmbus_chan_sched() might call the netvsc driver callback function that
> ends up scheduling NAPI work.  This "work" can access the channel ring
> buffer, so we must ensure that any such work is completed and that the
> ring buffer is no longer being accessed before freeing the ring buffer
> data structure in the channel closure path.  To this end, disable NAPI
> before calling vmbus_close() in netvsc_device_remove().
> 
> Suggested-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: <netdev@...r.kernel.org>

Do you have a test that reproduces this issue?

The netvsc device is somewhat unique in that it needs NAPI
enabled on the primary channel to interact with the host.
Therefore it can't call napi_disable in the normal dev->stop() place.

Acked-by: Stephen Hemminger <stephen@...workplumber.org>