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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 20 Apr 2021 10:34:17 +0200
Message-ID: <CANn89iJLSmtBNoDo8QJ6a0MzsHjdLB0Pf=cs9e4g8Y6-KuFiMQ@mail.gmail.com>
Subject: Re: [PATCH] net: called rtnl_unlock() before runpm resumes devices
To:     AceLan Kao <acelan.kao@canonical.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        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>
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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

By doing so, you give more chances for reviewers to understand why the
fix is not risky,
and help stable teams work.

Thanks.

> Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
> ---
>  net/core/dev.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1f79b9aa9a3f..427cbc80d1e5 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1537,8 +1537,11 @@ static int __dev_open(struct net_device *dev, struct netlink_ext_ack *extack)
>
>         if (!netif_device_present(dev)) {
>                 /* may be detached because parent is runtime-suspended */
> -               if (dev->dev.parent)
> +               if (dev->dev.parent) {
> +                       rtnl_unlock();
>                         pm_runtime_resume(dev->dev.parent);
> +                       rtnl_lock();
> +               }
>                 if (!netif_device_present(dev))
>                         return -ENODEV;
>         }
> --
> 2.25.1
>