netdev - Re: [PATCH 1/2] virtio-net: fix possible dim status unrecoverable

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Message-ID: <8d829442-0eef-485c-b448-cd2376c20270@linux.alibaba.com>
Date: Mon, 25 Mar 2024 10:11:16 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev,
 "Michael S. Tsirkin" <mst@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
 "David S. Miller" <davem@...emloft.net>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] virtio-net: fix possible dim status unrecoverable



在 2024/3/22 下午1:17, Jason Wang 写道:
> On Thu, Mar 21, 2024 at 7:46 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>> When the dim worker is scheduled, if it fails to acquire the lock,
>> dim may not be able to return to the working state later.
>>
>> For example, the following single queue scenario:
>>    1. The dim worker of rxq0 is scheduled, and the dim status is
>>       changed to DIM_APPLY_NEW_PROFILE;
>>    2. The ethtool command is holding rtnl lock;
>>    3. Since the rtnl lock is already held, virtnet_rx_dim_work fails
>>       to acquire the lock and exits;
>>
>> Then, even if net_dim is invoked again, it cannot work because the
>> state is not restored to DIM_START_MEASURE.
>>
>> Fixes: 6208799553a8 ("virtio-net: support rx netdim")
>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>> ---
>>   drivers/net/virtio_net.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index c22d111..0ebe322 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -3563,8 +3563,10 @@ static void virtnet_rx_dim_work(struct work_struct *work)
>>          struct dim_cq_moder update_moder;
>>          int i, qnum, err;
>>
>> -       if (!rtnl_trylock())
>> +       if (!rtnl_trylock()) {
>> +               schedule_work(&dim->work);
>>                  return;
>> +       }
> Patch looks fine but I wonder if a delayed schedule is better.

The work in net_dim() core layer uses non-delayed-work, and the two 
cannot be mixed.

Thanks,
Heng

>
> Thanks
>
>>          /* Each rxq's work is queued by "net_dim()->schedule_work()"
>>           * in response to NAPI traffic changes. Note that dim->profile_ix
>> --
>> 1.8.3.1
>>