virtio block device hangs after "virtio_blk virtio3: requests:id 0 is not a head!"

The virtual machine is running block layer workloads, interrupted by unclean reboots (echo b > /proc/sysrq-trigger). Kernel version is 3.14.

Sometimes, I get this message on boot:

"virtio_blk virtio3: requests:id 0 is not a head!"

Then, I/O to the virtio block devices just hangs.

Unfortunately I don't have a test case and this is kind of hard to reproduce, but it seems related to having I/O in flight when the kernel is forced to reboot.

On Wed, Aug 20, 2014 at 08:37:46PM -0000, Slava Pestov wrote:
> The virtual machine is running block layer workloads, interrupted by
> unclean reboots (echo b > /proc/sysrq-trigger). Kernel version is 3.14.
> 
> Sometimes, I get this message on boot:
> 
> "virtio_blk virtio3: requests:id 0 is not a head!"
> 
> Then, I/O to the virtio block devices just hangs.
> 
> Unfortunately I don't have a test case and this is kind of hard to
> reproduce, but it seems related to having I/O in flight when the kernel
> is forced to reboot.

Hi Slava,
Sounds like the virtio device was not reset properly.

The guest kernel is looking for completed responses from the host.  The
host has indicated that descriptor 0 is the next completed response but
the guest does not remember having submitted it.

Do you have a kernel stack trace when this was encountered?

Stefan


You mean a kernel stack trace when the message was printed? I don't have that but I guess I could add a dump_stack() call in there.

Triaging old bug tickets ... can you still reproduce this issue with the latest version of QEMU and the kernel?

[Expired for QEMU because there has been no activity for 60 days.]