Re: [PATCH] vhost: add runtime locking check in unsafe APIs

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Jiayu,

On 5/10/22 11:00, Hu, Jiayu wrote:
> Hi Maxime,
> 
> This is a good idea to add the lock check below. But I have two
> questions:
> First, rte_vhost_clear_queue_thread_unsafe() is thread unsafe.
> Why doesn't add the check for it?

Yes, I missed it. Thanks for spotting that!

> Second, dev->notify_ops->destroy_device() is called without taking
> the lock. If vhost applications try to clear inflight packets or even
> unregister asynchronous data-path in this callback, rather than in
> dev->notify_ops->vring_state_changed(), asynchronous APIs below
> will return -1. How to handle this situation?

You should call the proper safe/unsafe API depending on the context.
The idea of this patch was to catch corner cases like this one, so good
it helped to identify this issue.

Thanks,
Maxime

> Thanks,
> Jiayu
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Tuesday, May 10, 2022 4:25 PM
>> To: dev@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; Ding, Xuan
>> <xuan.ding@intel.com>; Hu, Jiayu <jiayu.hu@intel.com>; Jiang, Cheng1
>> <cheng1.jiang@intel.com>; Pai G, Sunil <sunil.pai.g@intel.com>;
>> david.marchand@redhat.com
>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Subject: [PATCH] vhost: add runtime locking check in unsafe APIs
>>
>> This patch adds runtime checks in unsafe Vhost async APIs, to ensure the
>> access lock is taken.
>>
>> The detection won't work every time, as another thread could take the lock,
>> but it would help to detect misuse of these unsafe API.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   lib/vhost/vhost.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c index
>> df0bb9d043..39cbeb415c 100644
>> --- a/lib/vhost/vhost.c
>> +++ b/lib/vhost/vhost.c
>> @@ -1732,6 +1732,12 @@
>> rte_vhost_async_channel_register_thread_unsafe(int vid, uint16_t queue_id)
>>   	if (unlikely(vq == NULL || !dev->async_copy))
>>   		return -1;
>>
>> +	if (unlikely(!rte_spinlock_is_locked(&vq->access_lock))) {
>> +		VHOST_LOG_CONFIG(ERR, "(%s) %s() called without access
>> lock taken.\n",
>> +				dev->ifname, __func__);
>> +		return -1;
>> +	}
>> +
>>   	return async_channel_register(vid, queue_id);  }
>>
>> @@ -1796,6 +1802,12 @@
>> rte_vhost_async_channel_unregister_thread_unsafe(int vid, uint16_t
>> queue_id)
>>   	if (vq == NULL)
>>   		return -1;
>>
>> +	if (unlikely(!rte_spinlock_is_locked(&vq->access_lock))) {
>> +		VHOST_LOG_CONFIG(ERR, "(%s) %s() called without access
>> lock taken.\n",
>> +				dev->ifname, __func__);
>> +		return -1;
>> +	}
>> +
>>   	if (!vq->async)
>>   		return 0;
>>
>> @@ -1925,6 +1937,12 @@ rte_vhost_async_get_inflight_thread_unsafe(int
>> vid, uint16_t queue_id)
>>   	if (vq == NULL)
>>   		return ret;
>>
>> +	if (unlikely(!rte_spinlock_is_locked(&vq->access_lock))) {
>> +		VHOST_LOG_CONFIG(ERR, "(%s) %s() called without access
>> lock taken.\n",
>> +				dev->ifname, __func__);
>> +		return -1;
>> +	}
>> +
>>   	if (!vq->async)
>>   		return ret;
>>
>> --
>> 2.35.1
>