Re: [dpdk-dev] [PATCH v2] vhost: flush used->idx update before reading avail->flags

[Nikita Kalyazin <n.kalyazin@samsung.com>]

Hi,


Maybe I missed a part of the discussion, but is there any special purpose for using rte_mb (both read and write fence) here rather than rte_wmb (write fence only)?

-- 

Best regards,

Nikita Kalyazin,
n.kalyazin@samsung.com

Software Engineer
CE OS Group
Samsung R&D Institute Russia
Tel: +7 (495) 797-25-00 #3816
Tel: +7 (495) 797-25-03
Office #1501, 12-1, Dvintsev str.,
Moscow, 127018, Russia

On Wed, May 13, 2015 at 12:46:30PM +0200, Thomas Monjalon wrote:
> 2015-04-29 19:11, Huawei Xie:
> > update of used->idx and read of avail->flags could be reordered.
> > memory fence should be used to ensure the order, otherwise guest could see a stale used->idx value after it toggles the interrupt suppression flag.
> > After guest sets the interrupt suppression flag, it will check if there is more buffer to process through used->idx. If it sees a stale value, it will exit the processing while host willn't send interrupt to guest.
> > 
> > Signed-off-by: Huawei Xie <huawei.xie@intel.com>
> 
> Applied with following title, thanks
> 	vhost: fix virtio freeze due to missed interrupt
>