netdev - Re: [Patch net] ipv6: only call ip6_route_dev_notify() once for NETDEV

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Message-ID: <5949E17A.4020508@rock-chips.com>
Date:   Wed, 21 Jun 2017 11:01:14 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
CC:     David Ahern <dsahern@...il.com>
Subject: Re: [Patch net] ipv6: only call ip6_route_dev_notify() once for NETDEV_UNREGISTER

Hi Cong Wang,

i don't know much about net core, maybe i'm misreading the code...but

On 06/21/2017 02:42 AM, Cong Wang wrote:
> In commit 242d3a49a2a1 ("ipv6: reorder ip6_route_dev_notifier after ipv6_dev_notf")
> I assumed NETDEV_REGISTER and NETDEV_UNREGISTER are paired,
> unfortunately, as reported by jeffy, netdev_wait_allrefs()
> could rebroadcast NETDEV_UNREGISTER event until all refs are
> gone.
>
> We have to add an additional check to avoid this corner case.
> For netdev_wait_allrefs() dev->reg_state is NETREG_UNREGISTERED,
> for dev_change_net_namespace(), dev->reg_state is
> NETREG_REGISTERED. So check for dev->reg_state != NETREG_UNREGISTERED.

i saw we are calling NETDEV_REGISTER in these cases:
1/ register_netdevice_notifier:
the paired unregister would be:
a) normal unregister: rollback_registered_many
b) the error path:
register_netdevice_notifier->rollback jump label

2/ register_netdevice:
the paired unregister would both be rollback_registered_many for 
normal/error cases

3/ dev_change_net_namespace:
the paired unregister is the one right before the register notify

i think we are handling all register notifies, but only unregister 
notify from rollback_registered_many now?


>
> Fixes: 242d3a49a2a1 ("ipv6: reorder ip6_route_dev_notifier after ipv6_dev_notf")
> Reported-by: jeffy <jeffy.chen@...k-chips.com>
> Cc: David Ahern <dsahern@...il.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>   net/ipv6/route.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 7cebd95..322bd62 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3722,7 +3722,11 @@ static int ip6_route_dev_notify(struct notifier_block *this,
>   		net->ipv6.ip6_blk_hole_entry->dst.dev = dev;
>   		net->ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_get(dev);
>   #endif
> -	 } else if (event == NETDEV_UNREGISTER) {
> +	 } else if (event == NETDEV_UNREGISTER &&
> +		    dev->reg_state != NETREG_UNREGISTERED) {
> +		/* NETDEV_UNREGISTER could be fired for multiple times by
> +		 * netdev_wait_allrefs(). Make sure we only call this once.
> +		 */
>   		in6_dev_put(net->ipv6.ip6_null_entry->rt6i_idev);
>   #ifdef CONFIG_IPV6_MULTIPLE_TABLES
>   		in6_dev_put(net->ipv6.ip6_prohibit_entry->rt6i_idev);
>