netdev - Re: [Patch net 8/9] act_ife: move tcfa

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Message-Id: <20180820.112952.2052634913677104782.davem@davemloft.net>
Date:   Mon, 20 Aug 2018 11:29:52 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, vladbu@...lanox.com
Subject: Re: [Patch net 8/9] act_ife: move tcfa_lock down to where necessary

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Sun, 19 Aug 2018 12:22:12 -0700

> The only time we need to take tcfa_lock is when adding
> a new metainfo to an existing ife->metalist. We don't need
> to take tcfa_lock so early and so broadly in tcf_ife_init().
> 
> This means we can always take ife_mod_lock first, avoid the
> reverse locking ordering warning as reported by Vlad.
> 
> Reported-by: Vlad Buslov <vladbu@...lanox.com>
> Tested-by: Vlad Buslov <vladbu@...lanox.com>
> Cc: Vlad Buslov <vladbu@...lanox.com>
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

After this change we no longer call populate_metalist() in an atomic
context via tcf_ife_init(), and populate_metalist passes 'exists'
down to add_metainfo() as an 'atomic' indicator.  It doesn't have this
meaning if you aren't holding the tcfa_lock in the callers with BH
disabled.

Therefore, add_metainfo()'s 'atomic' indication is inaccurate in this
call chain and will use GFP_ATOMIC unnecessarily.

Probably the thing to just is just pass 'false' down to add_metainfo()
in populate_metalist().