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

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Message-Id: <20140318.143832.200632497327778756.davem@davemloft.net>
Date:	Tue, 18 Mar 2014 14:38:32 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	cwang@...pensource.com
Cc:	ebiederm@...ssion.com, stephen@...workplumber.org,
	eric.dumazet@...il.com, netdev@...r.kernel.org,
	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

From: Cong Wang <cwang@...pensource.com>
Date: Tue, 18 Mar 2014 11:26:54 -0700

> 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.

Right, this is bogus.
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