netdev - Re: [PATCH 3/6] netpoll: Don't allow on devices that perform their own xmit locking

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Date:	Tue, 18 Mar 2014 11:26:54 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	David Miller <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Cong Wang <xiyou.wangcong@...il.com>, mpm@...enic.com,
	satyam.sharma@...il.com
Subject: Re: [PATCH 3/6] netpoll: Don't allow on devices that perform their
 own xmit locking

On Mon, Mar 17, 2014 at 11:25 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> There are strong and reasonable assumptions in the netpoll code that the
> transmit code for network devices will not perform their own locking,
> that can easily lead to deadlock if the assumptions are violated.
>
> Document those assumptions by verifying the network device on which
> netpoll is enabled does not have NETIF_F_LLTX set in netdev->features.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  net/core/netpoll.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index 825200fcb0ff..a9abb195a2c3 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -606,6 +606,7 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
>         INIT_WORK(&np->cleanup_work, netpoll_async_cleanup);
>
>         if ((ndev->priv_flags & IFF_DISABLE_NETPOLL) ||
> +           (ndev->features & NETIF_F_LLTX) ||
>             !ndev->netdev_ops->ndo_poll_controller) {
>                 np_err(np, "%s doesn't support polling, aborting\n",
>                        np->dev_name);

Hmm? This basically disables netpoll on a lots of devices, such as vlan.
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