Linux Virtualization - Aug 2014 - When I boot two virtio-rng devices, guest will hang

On Mon, Jul 28, 2014 at 02:42:13PM +0530, Amit Shah
wrote:
> On (Mon) 28 Jul 2014 [16:49:20], Amos Kong wrote:
> > On Mon, Jul 28, 2014 at 01:25:14PM +0530, Amit Shah wrote:
> > > On (Mon) 28 Jul 2014 [15:32:42], Amos Kong wrote:
> > > > QEMU commandline:
> > > > 
> > > > ./x86_64-softmmu/qemu-system-x86_64 --enable-kvm   -m 2000
-drive file=/images/nolvm.qcow2 --kernel /home/devel/linux/arch/x86/boot/bzImage
-append "ro root=/dev/sda1 console=ttyS0,115200"  -monitor
unix:/tmp/m,nowait,server -device
virtio-net-pci,netdev=h0,vectors=17,mq=on,id=n0 -netdev tap,id=h0,queues=8
-device virtio-net-pci,netdev=h1,vectors=0,mq=on,id=n1 -netdev
tap,id=h1,queues=8  -vnc :0 -mon chardev=qmp,mode=control,pretty=on -chardev
socket,id=qmp,host=localhost,port=1234,server,nowait -serial stdio -object
rng-random,filename=/dev/urandom,id=rng0   -device virtio-rng-pci,rng=rng0,id=h0
-object rng-random,filename=/dev/urandom,id=rng1   -device
virtio-rng-pci,rng=rng1,id=h1
> > > > 
> > > > It works when I only add one virtio-rng device. Did you
touch this
> > > > problem?
> > > > 
> > > > I'm using latest net-next/master
(ac3d2e5a9ef2f4d8f57c50070c4883ecb7cec29f)
> >  
> > Hi Amit,
> > 
> > > <snip>
> > > > [    0.223503] Non-volatile memory driver v1.3
> > > > [    1.172293] tsc: Refined TSC clocksource calibration:
2893.436 MHz
> > > > qemu: terminating on signal 2           <---------- (I
have to cancel QEMU process by Ctrl + C)
> > > 
> > > This looks similar to what I saw when driver asks for randomness
from the host
> > > before probe is completed.
> > > 
> > > Does the following patch help?
> > 
> > This patch was already inclued in latest net-next/master
> > patch commit: e052dbf554610e2104c5a7518c4d8374bed701bb
> 
> No, it's a different one, goes on top of the commit you referenced.
 
Thanks. This patch fixed the problem.

-- 
			Amos.

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.


(The difference between /dev/random and /dev/urandom is the speed.)

Thanks, Amos

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.