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 21:39:51 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Zoltan Kiss <zoltan.kiss@...rix.com>, <netdev@...r.kernel.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	<xen-devel@...ts.xen.org>
Subject: Re: [Xen-devel] [PATCH net v2 2/3] xen-netback: don't stop dealloc
 kthread too early

On Mon, Aug 11, 2014 at 04:23:28PM +0100, David Vrabel wrote:
> On 11/08/14 15:44, Wei Liu wrote:
> > 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());
> 
> This will never sleep if the thread is being stopped when there are
> packets in flight.
> 

Good catch.
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