linux-kernel - Re: [PATCH bpf v4 2/2] xdp: fix hang while unregistering device bound to xdp socket

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Date:   Thu, 27 Jun 2019 10:23:27 +0300
From:   Ilya Maximets <i.maximets@...sung.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, xdp-newbies@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf v4 2/2] xdp: fix hang while unregistering device
 bound to xdp socket

On 26.06.2019 21:34, Jakub Kicinski wrote:
> On Wed, 26 Jun 2019 21:15:15 +0300, Ilya Maximets wrote:
>> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
>> index 267b82a4cbcf..56729e74cbea 100644
>> --- a/net/xdp/xdp_umem.c
>> +++ b/net/xdp/xdp_umem.c
>> @@ -140,34 +140,38 @@ int xdp_umem_assign_dev(struct xdp_umem *umem, struct net_device *dev,
>>  	return err;
>>  }
>>  
>> -static void xdp_umem_clear_dev(struct xdp_umem *umem)
>> +void xdp_umem_clear_dev(struct xdp_umem *umem)
>>  {
>> +	bool lock = rtnl_is_locked();
> 
> How do you know it's not just locked by someone else?  You need to pass
> the locked state in if this is called from different paths, some of
> which already hold rtnl.

Oh. That's a shame. I need more sleep.

Thanks for spotting. I'll re-work this part.

Best regards, Ilya Maximets.

> 
> Preferably factor the code which needs the lock out into a separate
> function like this:
> 
> void __function()
> {
> 	do();
> 	the();
> 	things();
> 	under();
> 	the();
> 	lock();
> }
> 
> void function()
> {
> 	rtnl_lock();
> 	__function();
> 	rtnl_unlock();
> }
> 
>>  	struct netdev_bpf bpf;
>>  	int err;
>>  
>> +	if (!lock)
>> +		rtnl_lock();
> 
> 
>