On Tue, Oct 20, 2020 at 12:41 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
On Mon, Oct 19, 2020 at 11:56:35PM +0800, 谢永吉 wrote:
>
>
>
> On Mon, Oct 19, 2020 at 11:47 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Mon, Oct 19, 2020 at 11:44:36PM +0800, 谢永吉 wrote:
> >
> >
> > On Mon, Oct 19, 2020 at 11:05 PM Michael S. Tsirkin <mst@xxxxxxxxxx>
> wrote:
> >
> > On Mon, Oct 19, 2020 at 10:56:22PM +0800, Xie Yongji wrote:
> > > The module should not be unloaded if any vduse device exists.
> > > So increase the module's reference count when creating vduse
> > > device. And the reference count is kept until the device is
> > > destroyed.
> > >
> > > Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
> > > ---
> > > drivers/vdpa/vdpa_user/vduse_dev.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/
> vdpa_user/
> > vduse_dev.c
> > > index 6787ba66725c..f04aa02de8c1 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -887,6 +887,7 @@ static int vduse_destroy_dev(u32 id)
> > > kfree(dev->vqs);
> > > vduse_iova_domain_destroy(dev->domain);
> > > vduse_dev_destroy(dev);
> > > + module_put(THIS_MODULE);
> > >
> > > return 0;
> > > }
> > > @@ -931,6 +932,7 @@ static int vduse_create_dev(struct
> vduse_dev_config
> > *config)
> > >
> > > dev->connected = true;
> > > list_add(&dev->list, &vduse_devs);
> > > + __module_get(THIS_MODULE);
> > >
> > > return fd;
> > > err_fd:
> >
> > This kind of thing is usually an indicator of a bug. E.g.
> > if the refcount drops to 0 on module_put(THIS_MODULE) it
> > will be unloaded and the following return will not run.
> >
> >
> >
> > Should this happen? The refcount should be only decreased to 0 after the
> > misc_device is closed?
> >
> > Thanks,
> > Yongji
> >
>
> OTOH if it never drops to 0 anyway then why do you need to increase it?
>
>
>
> To prevent unloading the module in the case that the device is created, but no
> user process using it (e.g. the user process crashed).
>
> Thanks,
> Yongji
Looks like it can drop to 0 if that is the case then?
Could you give me an example? In my understanding, vduse_create_dev() should be called only after we open the chardev which will grab the module's reference.
Thanks,
Yongji
