On Thu, 19 Jan 2023 15:07:01 -0400 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > 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 Also revise the commit log since we'll be taking a reference in the group model as well. The function and comments should also be updated s/destroy/release/. Thanks, Alex
