On 2/16/23 08:40, Keith Busch wrote:

On Thu, Feb 16, 2023 at 12:50:03PM +0100, Hannes Reinecke wrote:

quoted

Hi all,

it has come up in other threads, so it might be worthwhile to have its own
topic:

Userspace command aborts

As it stands we cannot abort I/O commands from userspace.
This is hitting us when running in a virtual machine:
The VM sets a timeout when submitting a command, but that
information can't be transmitted to the VM host. The VM host
then issues a different command (with another timeout), and
again that timeout can't be transmitted to the attached devices.
So when the VM detects a timeout, it will try to issue an abort,
but that goes nowhere as the VM host has no way to abort commands
from userspace.
So in the end the VM has to wait for the command to complete, causing
stalls in the VM if the host had to undergo error recovery or something.

Aborts are racy. A lot of hardware implements these as a no-op, too.
  

I'd avoid implementing userspace aborts and fix things in spec first.

-ck