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Date: Mon, 11 Aug 2014 15:31:07 +0100 From: Wei Liu <wei.liu2@...rix.com> To: David Vrabel <david.vrabel@...rix.com> CC: Wei Liu <wei.liu2@...rix.com>, <netdev@...r.kernel.org>, <xen-devel@...ts.xen.org>, Ian Campbell <ian.campbell@...rix.com>, Zoltan Kiss <zoltan.kiss@...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 02:58:13PM +0100, 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(;;)). > Unfortunately this approach is bogus. If xenbus thread is not blocked it can free up various resources while dealloc thread is running -- queue can be gone under dealloc thread's feet. Wei. > David -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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