linux-kernel - Re: [PATCH] Fix tun: wake up waitqueues after IFF

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Date:   Mon, 17 Jun 2019 16:10:12 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Fei Li <lifei.shirley@...edance.com>, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     zhengfeiran@...edance.com, duanxiongchun@...edance.com
Subject: Re: [PATCH] Fix tun: wake up waitqueues after IFF_UP is set


On 2019/6/17 下午3:33, Fei Li wrote:
> Currently after setting tap0 link up, the tun code wakes tx/rx waited
> queues up in tun_net_open() when .ndo_open() is called, however the
> IFF_UP flag has not been set yet. If there's already a wait queue, it
> would fail to transmit when checking the IFF_UP flag in tun_sendmsg().
> Then the saving vhost_poll_start() will add the wq into wqh until it
> is waken up again. Although this works when IFF_UP flag has been set
> when tun_chr_poll detects; this is not true if IFF_UP flag has not
> been set at that time. Sadly the latter case is a fatal error, as
> the wq will never be waken up in future unless later manually
> setting link up on purpose.
>
> Fix this by moving the wakeup process into the NETDEV_UP event
> notifying process, this makes sure IFF_UP has been set before all
> waited queues been waken up.
>
> Signed-off-by: Fei Li <lifei.shirley@...edance.com>
> ---
>   drivers/net/tun.c | 17 +++++++++--------
>   1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index c452d6d831dd..a3c9cab5a4d0 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1015,17 +1015,9 @@ static void tun_net_uninit(struct net_device *dev)
>   static int tun_net_open(struct net_device *dev)
>   {
>   	struct tun_struct *tun = netdev_priv(dev);
> -	int i;
>   
>   	netif_tx_start_all_queues(dev);
>   
> -	for (i = 0; i < tun->numqueues; i++) {
> -		struct tun_file *tfile;
> -
> -		tfile = rtnl_dereference(tun->tfiles[i]);
> -		tfile->socket.sk->sk_write_space(tfile->socket.sk);
> -	}
> -
>   	return 0;
>   }
>   
> @@ -3634,6 +3626,7 @@ static int tun_device_event(struct notifier_block *unused,
>   {
>   	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
>   	struct tun_struct *tun = netdev_priv(dev);
> +	int i;
>   
>   	if (dev->rtnl_link_ops != &tun_link_ops)
>   		return NOTIFY_DONE;
> @@ -3643,6 +3636,14 @@ static int tun_device_event(struct notifier_block *unused,
>   		if (tun_queue_resize(tun))
>   			return NOTIFY_BAD;
>   		break;
> +	case NETDEV_UP:
> +		for (i = 0; i < tun->numqueues; i++) {
> +			struct tun_file *tfile;
> +
> +			tfile = rtnl_dereference(tun->tfiles[i]);
> +			tfile->socket.sk->sk_write_space(tfile->socket.sk);
> +		}
> +		break;
>   	default:
>   		break;
>   	}


Acked-by: Jason Wang <jasowang@...hat.com)