linux-kernel - Re: [PATCH net-next] net: core: fix the order in dev_put() and rtnl

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Message-ID: <903c5bed-5958-8888-b55d-9c175664b2a1@gmail.com>
Date:   Mon, 13 Sep 2021 22:18:13 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yajun Deng <yajun.deng@...ux.dev>, davem@...emloft.net,
        kuba@...nel.org
Cc:     nikolay@...dia.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: core: fix the order in dev_put() and
 rtnl_lock()



On 9/13/21 8:01 PM, Yajun Deng wrote:
> The dev_put() should be after rtnl_lock() in case for race.
> 
> Fixes: 893b19587534 ("net: bridge: fix ioctl locking")
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>  net/core/dev_ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
> index 0e87237fd871..9796fa35fe88 100644
> --- a/net/core/dev_ioctl.c
> +++ b/net/core/dev_ioctl.c
> @@ -384,8 +384,8 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
>  		dev_hold(dev);
>  		rtnl_unlock();
>  		err = br_ioctl_call(net, netdev_priv(dev), cmd, ifr, NULL);
> -		dev_put(dev);
>  		rtnl_lock();
> +		dev_put(dev);
>  		return err;
>  
>  	case SIOCSHWTSTAMP:
> 

What race exactly are you trying to avoid ?

This patch does not look needed to me.