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

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Message-ID: <2d95cda0-22e2-0f4f-3dc3-e7a1df4b68ee@mojatatu.com>
Date:   Mon, 13 Aug 2018 13:23:37 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Vlad Buslov <vladbu@...lanox.com>, netdev@...r.kernel.org
Cc:     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 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.

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

cheers,
jamal