netdev - Re: [PATCH net] ipv6: sr: fix scheduling in RCU when creating seg6 lwtunnel state

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Date:   Tue, 20 Mar 2018 17:11:19 +0000
From:   David Lebrun <dav.lebrun@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Cc:     David Lebrun <dlebrun@...gle.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net] ipv6: sr: fix scheduling in RCU when creating seg6
 lwtunnel state

On 20/03/18 15:07, Eric Dumazet wrote:
> This is not the proper fix.
> 
> Control path holds RTNL and can sleeep if needed.
> 
> RCU should be avoided in lwtunnel_build_state()
> 

+Roopa

In lwtunnel_build_state(), the RCU protects the lwtunnel_encap_ops "ops" 
which is rcu-dereferenced. Moreover, the lwtunnel_state_alloc() 
function, which is used in all build_state functions, also uses 
GFP_ATOMIC, so this seemed a proper fix, or at least proper mitigation.

Do you suggest that the lwtunnel_encap_ops can be protected in a 
different way, not requiring RCU ?