netdev - Re: [PATCH net 2/2] net: bridge: fix lockdep multicast

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Date:   Tue, 27 Apr 2021 00:17:52 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Nikolay Aleksandrov <nikolay@...dia.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     davem@...emloft.net, kuba@...nel.org, dsahern@...nel.org,
        yoshfuji@...ux-ipv6.org, netdev@...r.kernel.org,
        j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net,
        roopa@...dia.com, ast@...nel.org, andriin@...com,
        daniel@...earbox.net, weiwan@...gle.com, cong.wang@...edance.com,
        bjorn@...nel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net 2/2] net: bridge: fix lockdep multicast_lock false
 positive splat

On 4/26/21 10:15 PM, Nikolay Aleksandrov wrote:
 > On 26/04/2021 15:48, Herbert Xu wrote:

Hi Nikolay and Herbert,
Thank you for the reviews!

 >> On Sun, Apr 25, 2021 at 07:45:27PM +0300, Nikolay Aleksandrov wrote:
 >>>
 >>> Ugh.. that's just very ugly. :) The setup you've described above is 
by all means invalid, but
 >>> possible unfortunately. The bridge already checks if it's being 
added as a port to another
 >>> bridge, but not through multiple levels of indirection. These locks 
are completely unrelated
 >>> as they're in very different contexts (different devices).
 >>
 >> Surely we should forbid this? Otherwise what's to stop someone
 >> from creating a loop?
 >>
 >> Cheers,
 >>
 >
 > Indeed that would be best, it's very easy to loop them.
 >

We can make very various interface graphs with master/slave interface types.
So, if we need something to forbid it, I think it should be generic 
code, not only for the bridge module.