[Qemu-devel] [PATCH 0/2] vhost-user race condition on shutdown

[Dan Streetman]

From: Dan Streetman <address@hidden>

Buglink: https://launchpad.net/bugs/1823458

This is a race condition between the normal shutdown of a guest
and the handling of its vhost-user net being externally closed.
It's explained in more detail at the bug link; the short version
is that there are 2 problems, fixed by the 2 patches.  The first
patch fixes the race condition where multiple threads call
vhost_net_stop(), and the second patch prevents vhost-user from
calling vhost_net_cleanup() on CHR_EVENT_CLOSED, because it will
be cleaned up later and its fields will be accessed when
vhost_net_stop() is called later.

As explained in the bug report, this requires a rather complicated
setup to reproduce, and I'm not able to create a setup to reproduce
it myself.  However this has been reported to me/Canonical, and the
reporter is able to reproduce it consistently, so I've used them for
debug and testing.  This reproduction was done with the older 2.5
qemu, from Ubuntu Xenial; but the problem does still appear to exist
in upstream qemu, based on review of the code, which is why I'm sending
these patches.

Dan Streetman (2):
  add VirtIONet vhost_stopped flag to prevent multiple stops
  do not call vhost_net_cleanup() on running net from char user event

 hw/net/virtio-net.c            | 3 ++-
 include/hw/virtio/virtio-net.h | 1 +
 net/vhost-user.c               | 1 -
 3 files changed, 3 insertions(+), 2 deletions(-)

-- 
2.20.1