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

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@xmission.com>
---
 net/core/netpoll.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

On Mon, Mar 17, 2014 at 11:25 PM, Eric W. Biederman
<ebiederm@xmission.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@xmission.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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From: Cong Wang <cwang@twopensource.com>
Date: Tue, 18 Mar 2014 11:26:54 -0700

> On Mon, Mar 17, 2014 at 11:25 PM, Eric W. Biederman
> <ebiederm@xmission.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@xmission.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.

Right, this is bogus.
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