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

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Date:	Mon, 11 Aug 2014 15:44:41 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>, <netdev@...r.kernel.org>,
	<xen-devel@...ts.xen.org>, Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCH net v2 2/3] xen-netback: don't stop dealloc
 kthread too early

On Mon, Aug 11, 2014 at 03:13:41PM +0100, Zoltan Kiss wrote:
[...]
> > 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.

This snippet lacks change to while().

I would generally go for a shorter solution if the code is
self-explanatory.

@@ -2078,21 +2066,19 @@ int xenvif_dealloc_kthread(void *data)
 {
        struct xenvif_queue *queue = data;
 
-       while (!kthread_should_stop()) {
+       for (;;) {
                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) &&
+                   !tx_dealloc_work_todo(queue))
                        break;
 
                xenvif_tx_dealloc_action(queue);
                cond_resched();
        }
 
-       /* Unmap anything remaining*/
-       if (tx_dealloc_work_todo(queue))
-               xenvif_tx_dealloc_action(queue);
-
        return 0;
 }
 

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