Re: When I boot two virtio-rng devices, guest will hang

[Amos Kong <akong@redhat.com>]

On Tue, Aug 05, 2014 at 06:28:54PM +0800, Amos Kong wrote:
> 3.16 (guest hangs with two rng devices)
> 3.16 + quick fix (can startup with two rng devices) (hotplug issue 1 + hotplug issue 2 exist)
> lates torvalds/linux.git + amit 4 patches (can startup with two rng devices) (only hotplug issue 2 exists)
> 
> However, the 4 patches also fixed the hang issue, the hotplug issue was fixed a little.
> The hotplug issue is effected by the backend, or maybe it's not a real issue, because
> the rng device can be hot-removed after dd process is killed.
> 
> 
> Hotplug issue 1:
>   1. boot up guest with two rng device (rng0 uses /dev/urandom, rng1 uses /dev/random)
>   2. read data by dd in guest
>   3 (option 1). hot-remove rng0, then hot-remove rng1 -> result: _only rng1_ can't be removed until dd process is killed
>   3 (option 2). hot-remove rng1, then hot-remove rng0 -> result: two devices can be removed successfully, dd process will exit automatically.
> 
>   If we use /dev/urandom for rng0 and rng1, _rng0 & rng1_ can be removed, dd process will exit automatically.
> 
> Hotplug issue 2:
>   If we use /dev/random for rng0 and rng1, _rng0 & rng1_ can't be removed until dd process is killed.
> 
> Hotplug issue 3:
>   If we use /dev/random for rng0 and rng1, _only rng1_ can't be removed until dd process is killed.

Hi Amit,

I finally found the root problem and posted a fix to upstream:
  http://lists.linuxfoundation.org/pipermail/virtualization/2014-August/027049.html

It can help to fix the hotplug issues on 3.16 & latest kernel, so
stable kernel is CCed.

> (The difference between /dev/random and /dev/urandom is the speed.)
> 
> Thanks, Amos

-- 
			Amos.