On Tue, Jan 17, 2023 at 05:49:34AM -0800, Yi Liu wrote: > This is to avoid a circular refcount problem between the kvm struct and > the device file. KVM modules holds device/group file reference when the > device/group is added and releases it per removal or the last kvm reference > is released. This reference model is ok for the group since there is no > kvm reference in the group paths. > > But it is a problem for device file since the vfio devices may get kvm > reference in the device open path and put it in the device file release. > e.g. Intel kvmgt. This would result in a circular issue since the kvm > side won't put the device file reference if kvm reference is not 0, while > the vfio device side needs to put kvm reference in the release callback. > > To solve this problem for device file, let vfio provide release() which > would be called once kvm file is closed, it won't depend on the last kvm > reference. Hence avoid circular refcount problem. > > Suggested-by: Kevin Tian <kevin.tian@xxxxxxxxx> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx> > --- > virt/kvm/vfio.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> >From Alex's remarks please revise the commit message and add a Fixes line of some kind that this solves the deadlock Matthew was working on, and send it stand alone right away Jason
