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

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Message-ID: <10890d5f-4486-0fee-0d8e-3c1c92f78937@nvidia.com>
Date:   Tue, 14 Sep 2021 10:52:37 +0300
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Yajun Deng <yajun.deng@...ux.dev>, davem@...emloft.net,
        kuba@...nel.org
Cc:     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 14/09/2021 08:18, Eric Dumazet wrote:
> 
> 
> 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.
> 

+1 

There isn't a race there