linux-kernel - Re: [PATCH bpf v5 2/2] xdp: fix hang while unregistering device bound to xdp socket

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Message-ID: <2190070e-db72-6fbe-8dc9-7567847e48ff@samsung.com>
Date:   Fri, 28 Jun 2019 11:01:09 +0300
From:   Ilya Maximets <i.maximets@...sung.com>
To:     Jonathan Lemon <jonathan.lemon@...il.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>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf v5 2/2] xdp: fix hang while unregistering device
 bound to xdp socket

On 28.06.2019 1:04, Jonathan Lemon wrote:
> On 27 Jun 2019, at 3:15, Ilya Maximets wrote:
> 
>> Device that bound to XDP socket will not have zero refcount until the
>> userspace application will not close it. This leads to hang inside
>> 'netdev_wait_allrefs()' if device unregistering requested:
>>
>>   # ip link del p1
>>   < hang on recvmsg on netlink socket >
>>
>>   # ps -x | grep ip
>>   5126  pts/0    D+   0:00 ip link del p1
>>
>>   # journalctl -b
>>
>>   Jun 05 07:19:16 kernel:
>>   unregister_netdevice: waiting for p1 to become free. Usage count = 1
>>
>>   Jun 05 07:19:27 kernel:
>>   unregister_netdevice: waiting for p1 to become free. Usage count = 1
>>   ...
>>
>> Fix that by implementing NETDEV_UNREGISTER event notification handler
>> to properly clean up all the resources and unref device.
>>
>> This should also allow socket killing via ss(8) utility.
>>
>> Fixes: 965a99098443 ("xsk: add support for bind for Rx")
>> Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
>> ---
>>  include/net/xdp_sock.h |  5 +++
>>  net/xdp/xdp_umem.c     | 10 ++---
>>  net/xdp/xdp_umem.h     |  1 +
>>  net/xdp/xsk.c          | 87 ++++++++++++++++++++++++++++++++++++------
>>  4 files changed, 87 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
>> index d074b6d60f8a..82d153a637c7 100644
>> --- a/include/net/xdp_sock.h
>> +++ b/include/net/xdp_sock.h
>> @@ -61,6 +61,11 @@ struct xdp_sock {
>>      struct xsk_queue *tx ____cacheline_aligned_in_smp;
>>      struct list_head list;
>>      bool zc;
>> +    enum {
>> +        XSK_UNINITIALIZED = 0,
>> +        XSK_BINDED,
>> +        XSK_UNBINDED,
>> +    } state;
> 
> I'd prefer that these were named better, perhaps:
>    XSK_READY,
>    XSK_BOUND,
>    XSK_UNBOUND,

Sure. Thanks for suggestion!

> 
> Other than that:
> Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>
> 

I'll send a new version with the new state names keeping your ACK.

Best regards, Ilya Maximets.