linux-kernel - Re: [PATCH net-next v2] net: sched: don't disable bh when accessing action idr

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Message-ID: <vbfy3gaj1up.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Date:   Wed, 23 May 2018 09:57:34 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] net: sched: don't disable bh when accessing action idr


On Wed 23 May 2018 at 01:10, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Mon, May 21, 2018 at 1:03 PM, Vlad Buslov <vladbu@...lanox.com> wrote:
>> Initial net_device implementation used ingress_lock spinlock to synchronize
>> ingress path of device. This lock was used in both process and bh context.
>> In some code paths action map lock was obtained while holding ingress_lock.
>> Commit e1e992e52faa ("[NET_SCHED] protect action config/dump from irqs")
>> modified actions to always disable bh, while using action map lock, in
>> order to prevent deadlock on ingress_lock in softirq. This lock was removed
>> from net_device, so disabling bh, while accessing action map, is no longer
>> necessary.
>>
>> Replace all action idr spinlock usage with regular calls that do not
>> disable bh.
>
> While your patch is probably fine, the above justification seems not.

Sorry if I missed something. My justification is based on commit
description that added bh disable in subject code.

>
> In the past, tc actions could be released in BH context because tc
> filters use call_rcu(). However, I moved them to a workqueue recently.
> So before my change I don't think you can remove the BH protection,
> otherwise race with idr_remove()...

Found commit series that you described. Will modify commit message
accordingly.

Thanks,
Vlad