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From: Hangbin Liu <liuhangbin@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: netdev@vger.kernel.org, Stefano Brivio <sbrivio@redhat.com>,
	"David S . Miller" <davem@davemloft.net>,
	David Ahern <dsa@cumulusnetworks.com>
Subject: Re: [PATCH net] sit: use ipv6_mod_enabled to check if ipv6 is disabled
Date: Tue, 26 Feb 2019 09:43:21 +0800	[thread overview]
Message-ID: <20190226014321.GQ10051@dhcp-12-139.nay.redhat.com> (raw)
In-Reply-To: <1dd57d9d-fed2-67b8-ac28-7ef3681eeed2@gmail.com>

On Mon, Feb 25, 2019 at 08:39:27AM -0800, Eric Dumazet wrote:
> >> On 02/24/2019 08:12 PM, Hangbin Liu wrote:
> >>> ipv6_mod_enabled() is more safe and gentle to check if ipv6 is disabled
> >>> at running time.
> >>>
> >>
> >>
> >> Why is it better exactly ?
> >>
> >> IPv6 can be enabled on the host, but disabled per device
> >>
> >> /proc/sys/net/ipv6/conf/{name}/disable_ipv6
> > 
> > Sorry, it looks I didn't make it clear in the commit description.
> > This issue only occurs when IPv6 is disabled at boot time as there is
> > no IPv6 route entry. Disable ipv6 on specific interface is not affected.
> > So check ipv6_mod_enabled() is enough and we don't need to worry about
> > the rcu_read_lock or the dev status.
> > 
> > Should I update the commit description?
> 
> Certainly. Are you telling us skb->dev could be NULL here ?
> 
> Because rcu_read_lock() should already be asserted.
> 

No. I know skb->dev is not NULL and we have rcu_read_lock() here. But can we
guarantee the skb->dev won't be NULL forever? Maybe I'm a little sensitive.

I mean for only checking if ipv6 is disable at boot time, use
ipv6_mod_enabled() is more suitable.

Thanks
Hangbin

      parent reply	other threads:[~2019-02-26  1:43 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-25  4:12 [PATCH net] sit: use ipv6_mod_enabled to check if ipv6 is disabled Hangbin Liu
2019-02-25  4:24 ` Eric Dumazet
2019-02-25  8:17   ` Hangbin Liu
2019-02-25 16:39     ` Eric Dumazet
2019-02-25 16:57       ` David Ahern
2019-02-26  1:55         ` Hangbin Liu
2019-02-26  2:15           ` David Ahern
2019-02-26  4:08             ` Hangbin Liu
2019-02-26  4:36               ` Eric Dumazet
2019-02-26  1:43       ` Hangbin Liu [this message]

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