netdev - Re: [PATCH net-next] net: sched: act_ife: disable bh when taking ife_mod

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Date:   Mon, 13 Aug 2018 21:33:21 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        xiyou.wangcong@...il.com, jiri@...nulli.us
Subject: Re: [PATCH net-next] net: sched: act_ife: disable bh when taking ife_mod_lock


On Mon 13 Aug 2018 at 17:23, Jamal Hadi Salim <jhs@...atatu.com> wrote:
> On 2018-08-13 1:20 p.m., Vlad Buslov wrote:
>> Lockdep reports deadlock for following locking scenario in ife action:
>> 
>> Task one:
>> 1) Executes ife action update.
>> 2) Takes tcfa_lock.
>> 3) Waits on ife_mod_lock which is already taken by task two.
>> 
>> Task two:
>> 
>> 1) Executes any path that obtains ife_mod_lock without disabling bh (any
>> path that takes ife_mod_lock while holding tcfa_lock has bh disabled) like
>> loading a meta module, or creating new action.
>> 2) Takes ife_mod_lock.
>> 3) Task is preempted by rate estimator timer.
>> 4) Timer callback waits on tcfa_lock which is taken by task one.
>> 
>> In described case tasks deadlock because they take same two locks in
>> different order. To prevent potential deadlock reported by lockdep, always
>> disable bh when obtaining ife_mod_lock.
>> 
>
> Looks like your recent changes on net-next exposed this.

Its because I've recently expanded my private tests to create all kinds
of actions with estimator.

>
> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
>
> cheers,
> jamal