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Subject: Re: [PATCH] net: called rtnl_unlock() before runpm resumes devices
To:     AceLan Kao <acelan.kao@canonical.com>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andriin@fb.com>, Wei Wang <weiwan@google.com>,
        Cong Wang <cong.wang@bytedance.com>,
        Taehee Yoo <ap420073@gmail.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20210420075406.64105-1-acelan.kao@canonical.com>
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 <20210420122715.2066b537@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <CAFv23Q=ywiuZp7Y=bj=SAZmDdAnanAXA954hdO3GpkjmDo=RpQ@mail.gmail.com>
From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <c10a6c72-9db7-18c8-6b03-1f8c40b8fd87@gmail.com>
Date:   Thu, 22 Apr 2021 09:09:20 +0200
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On 22.04.2021 08:30, AceLan Kao wrote:
> Yes, should add
> 
> Fixes: 9474933caf21 ("igb: close/suspend race in netif_device_detach")
> and also
> Fixes: 9513d2a5dc7f ("igc: Add legacy power management support")
> 
Please don't top-post. Apart from that:
If the issue was introduced with driver changes, then adding a workaround
in net core may not be the right approach.

> Jakub Kicinski <kuba@kernel.org> 於 2021年4月21日 週三 上午3:27寫道：
>>
>> On Tue, 20 Apr 2021 10:34:17 +0200 Eric Dumazet wrote:
>>> On Tue, Apr 20, 2021 at 9:54 AM AceLan Kao <acelan.kao@canonical.com> wrote:
>>>>
>>>> From: "Chia-Lin Kao (AceLan)" <acelan.kao@canonical.com>
>>>>
>>>> The rtnl_lock() has been called in rtnetlink_rcv_msg(), and then in
>>>> __dev_open() it calls pm_runtime_resume() to resume devices, and in
>>>> some devices' resume function(igb_resum,igc_resume) they calls rtnl_lock()
>>>> again. That leads to a recursive lock.
>>>>
>>>> It should leave the devices' resume function to decide if they need to
>>>> call rtnl_lock()/rtnl_unlock(), so call rtnl_unlock() before calling
>>>> pm_runtime_resume() and then call rtnl_lock() after it in __dev_open().
>>>>
>>>>
>>>
>>> Hi Acelan
>>>
>>> When was the bugg added ?
>>> Please add a Fixes: tag
>>
>> For immediate cause probably:
>>
>> Fixes: 9474933caf21 ("igb: close/suspend race in netif_device_detach")
>>
>>> By doing so, you give more chances for reviewers to understand why the
>>> fix is not risky,
>>> and help stable teams work.
>>
>> IMO the driver lacks internal locking. Taking rtnl from resume is just
>> one example, git history shows many more places that lacked locking and
>> got papered over with rtnl here.