Re: [Xen-devel] [PATCH net v2 2/3] xen-netback: don't stop dealloc kthread too early

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 11/08/14 14:58, David Vrabel wrote:
> On 11/08/14 14:48, Wei Liu wrote:
>> On Mon, Aug 11, 2014 at 01:10:12PM +0100, David Vrabel wrote:
>>> On 08/08/14 17:37, Wei Liu wrote:
>> [...]
>>>>    if (tx_evtchn == rx_evtchn) {
>>>>            /* feature-split-event-channels == 0 */
>>>> @@ -687,6 +700,9 @@ void xenvif_disconnect(struct xenvif *vif)
>>>>                    queue->task = NULL;
>>>>            }
>>>>   
>>>> +          wait_event(queue->inflight_wq,
>>>> +                     atomic_read(&queue->inflight_packets) == 0);
>>>
>>> Just make the dealloc task not stop unless it has deallocated all
>>> outstanding requests.  There's no need for another wait queue here.
>>>
>>
>> Are you suggesting something like
>>
>>    while (atomic_read(&queue->inflight_packets) !=0)
>>      schedule_timeout(SOME_TIMEOUT);
> 
> No. That would be awful!
> 
> Add the test to the kthread itself:
> 
> int xenvif_dealloc_kthread(void *data)
> {
>       struct xenvif_queue *queue = data;
> 
>       while (atomic_read(&queue->inflight_packets) > 0
>                 || !kthread_should_stop()) {
>              [...]
> 
> etc.
> 
> Although, the main loop is a bit confused, so I suggest adding:
> 
> static bool xenvif_dealloc_thread_should_stop(struct xenvif_queue *q)
> {
>      /* Dealloc thread must remain running if there are any inflight
>       * packets so it can properly dealloc them when they complete.
>       */
>      return atomic_read(&queue->inflight_packets) == 0
>          && kthread_should_stop();
> }
> 
> And cleaning it up a bit (the while() could be a for(;;)).

I would recommend this:
---
@@ -2066,7 +2066,7 @@ int xenvif_dealloc_kthread(void *data)
                wait_event_interruptible(queue->dealloc_wq,
                                         tx_dealloc_work_todo(queue) ||
                                         kthread_should_stop());
-               if (kthread_should_stop())
+               if (kthread_should_stop() && 
!atomic_read(&queue->inflight_packets))
                        break;
 
                xenvif_tx_dealloc_action(queue);
---
If kthread_stop called, this will keep the main loop running until all 
callbacks are called.
Then it proceeds to the exit branch, otherwise doesn't disrupt normal operation.

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