netdev - Re: [PATCH net-next v2] ip_tunnel: Add dst_cache management lwtunnel

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Date:   Fri, 22 Feb 2019 10:03:25 -0500
From:   David Ahern <dsahern@...il.com>
To:     wenxu <wenxu@...oud.cn>, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] ip_tunnel: Add dst_cache management
 lwtunnel_state of ip tunnel

On 2/21/19 11:14 PM, wenxu wrote:
> build_state in the rcu_read_lock and disable the preempt
> 
>  rcu_read_lock();
>     ops = rcu_dereference(lwtun_encaps[encap_type]);
>     if (likely(ops && ops->build_state && try_module_get(ops->owner))) {
>         found = true;
>         ret = ops->build_state(encap, family, cfg, lws, extack);
>         if (ret)
>             module_put(ops->owner);
>     }  
>     rcu_read_unlock();
> 

Missed that.

Once a reference is taken the rcu_read_lock can be dropped before
calling build_state allowing the allocations to be GFP_KERNEL.