Re: [PATCH] net: called rtnl_unlock() before runpm resumes devices

[Eric Dumazet <edumazet@google.com>]

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
>