The kvmgt code keeps a pointer to the struct kvm associated with the
device, but doesn't actually hold a reference to it. If we do unclean
shutdown testing (ie. killing the user process), then we can see the
kvm association to the device unset, which causes kvmgt to trigger a
device release via a work queue. Naturally we cannot guarantee that
the cached struct kvm pointer is still valid at this point without
holding a reference. The observed failure in this case is a stuck
cpu trying to acquire the spinlock from the invalid reference, but
other failure modes are clearly possible. Hold a reference to avoid
this.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Cc: stable@vger.kernel.org #v4.10 Cc: Jike Song <jike.song@intel.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Zhenyu Wang <zhenyuw@linux.intel.com> Cc: Zhi Wang <zhi.a.wang@intel.com> Reviewed-by: Jike Song <jike.song@intel.com> Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>